TCF Financial 10-K 28 Feb 18 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 26, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	CHEMICAL FINANCIAL CORP
Entity Central Index Key	19,612
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 3,340
Entity Common Stock, Shares Outstanding		71,302,847

Consolidated Statements of Fina

Consolidated Statements of Financial Position - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cash and cash equivalents:
Cash and cash due from banks	$ 226,003	$ 237,758
Interest-bearing deposits with the Federal Reserve Bank and other banks	229,988	236,644
Total cash and cash equivalents	455,991	474,402
Investment securities:
Available-for-sale, at fair value	1,963,546	1,234,964
Held-to-maturity, at amortized cost (fair value of $662,906 and $608,531, respectively)	677,093	623,427
Total investment securities	2,640,639	1,858,391
Loans held-for-sale, at fair value	52,133	81,830
Loans	14,155,267	12,990,779
Allowance for loan losses	(91,887)	(78,268)
Net loans	14,063,380	12,912,511
Premises and equipment	126,896	145,012
Loan servicing rights ($63,841 and $48,085 measured at fair value, respectively)	63,841	58,315
Goodwill	1,134,568	1,133,534
Other intangible assets	34,271	40,211
Interest receivable and other assets	709,154	650,973
Total assets	19,280,873	17,355,179
Deposits:
Noninterest-bearing	3,725,779	3,341,520
Interest-bearing	9,917,024	9,531,602
Total deposits	13,642,803	12,873,122
Interest payable and other liabilities	181,203	134,637
Securities sold under agreements to repurchase with customers	415,236	343,047
Short-term borrowings	2,000,000	825,000
Long-term borrowings	372,882	597,847
Total liabilities	16,612,124	14,773,653
Shareholders' equity
Preferred stock, no par value: Authorized – 2,000,000 shares at 12/31/16 and 12/31/15	0	0
Common stock, $1 par value per share: Authorized — 100,000,000 shares at 12/31/16 and 60,000,000 shares at 12/31/15, Issued and outstanding — 70,599,133 shares at 12/31/16 and 38,167,861 shares at 12/31/15	71,207	70,599
Additional paid-in capital	2,203,637	2,210,762
Retained earnings	419,403	340,201
Accumulated other comprehensive loss	(25,498)	(40,036)
Total shareholders' equity	2,668,749	2,581,526
Total liabilities and shareholders' equity	$ 19,280,873	$ 17,355,179

Consolidated Statements of Fin3

Consolidated Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Held-to-maturity, fair value	$ 662,906	$ 608,531
Loan servicing rights, fair value	$ 63,841	$ 48,085
Preferred stock, no par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized	135,000,000	100,000,000
Common stock, shares issued	71,207,114	70,599,133
Common stock, shares outstanding	71,207,114	70,599,133

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income
Interest and fees on loans	$ 573,128	$ 383,545	$ 271,772
Interest on investment securities:
Taxable	31,496	10,989	8,786
Tax-exempt	18,343	12,317	9,073
Dividends on nonmarketable equity securities	4,924	1,973	1,648
Interest on deposits with the Federal Reserve Bank, other banks and Federal funds sold	4,244	1,555	510
Total interest income	632,135	410,379	291,789
Interest expense
Interest on deposits	46,727	23,021	15,406
Interest on short-term borrowings	20,321	1,660	453
Interest on long-term borrowings	7,509	4,617	1,922
Total interest expense	74,557	29,298	17,781
Net interest income	557,578	381,081	274,008
Provision for loan losses	23,300	14,875	6,500
Net interest income after provision for loan losses	534,278	366,206	267,508
Noninterest income
Service charges and fees on deposit accounts	35,001	28,136	25,481
Wealth management revenue	25,512	22,601	20,552
Other charges and fees for customer services	32,771	30,246	25,513
Net gain on sale of loans and other mortgage banking revenue	32,205	21,859	6,133
Net (loss) gain on sale of investment securities	(7,388)	129	630
Gain on sale of branch offices	0	7,391	0
Other	25,918	11,988	1,907
Total noninterest income	144,019	122,350	80,216
Operating expenses
Salaries, wages and employee benefits	213,828	165,213	127,920
Occupancy	30,554	23,525	18,213
Equipment and software	32,248	24,408	18,569
Outside processing and service fees	35,142	21,199	15,207
Merger expenses	8,522	61,134	7,804
Restructuring expenses	19,880	0	0
Other	81,820	42,939	36,181
Total operating expenses	421,994	338,418	223,894
Income before income taxes	256,303	150,138	123,830
Income tax expense	106,780	42,106	37,000
Net income	$ 149,523	$ 108,032	$ 86,830
Earnings per common share:
Basic (in dollars per share)	$ 2.11	$ 2.21	$ 2.41
Diluted (in dollars per share)	2.08	2.17	2.39
Cash dividends declared per common share (in dollars per share)	$ 1.10	$ 1.06	$ 1

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 149,523	$ 108,032	$ 86,830
Other Comprehensive Income (Loss), Net of Tax:
Unrealized holding gains (losses) on securities available-for-sale arising during the period	1,269	(18,723)	(1,952)
Reclassification adjustment for gains and losses on realized income	7,388	(129)	(630)
Tax effect	(3,029)	6,598	904
Net unrealized gains (losses) on securities available-for-sale, net of tax	5,628	(12,254)	(1,678)
Unrealized gains on interest rate swaps designated as cash flow hedges	4,263	0	0
Reclassification adjustment for losses included in net income	1,633	0	0
Tax effect	(2,064)	0	0
Net unrealized gains on interest rate swaps designated as cash flow hedges, net of tax	3,832	0	0
Plan remeasurement	13,011	(707)	0
Adjustment for pension and other postretirement benefits	1,752	2,630	7,845
Tax effect	(5,167)	(673)	(2,746)
Net adjustment for pension and other postretirement benefits	9,596	1,250	5,099
Other comprehensive income (loss), net of tax	19,056	(11,004)	3,421
Total comprehensive income, net of tax	$ 168,579	$ 97,028	$ 90,251

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2014		$ 797,133	$ 32,774	$ 565,166	$ 231,646	$ (32,453)
Changes in Stockholders' Equity
Comprehensive income		90,251			86,830	3,421
Cash dividends declared		(36,918)			(36,918)
Issuance of common stock and common stock equivalents in business combinations		159,904	5,183	154,721
Net shares issued under share-based compensation plans		2,126	200	1,926
Share-based compensation expense		3,478	11	3,467
Ending balance at Dec. 31, 2015		1,015,974	38,168	725,280	281,558	(29,032)
Changes in Stockholders' Equity
Comprehensive income		97,028			108,032	(11,004)
Cash dividends declared		(49,389)			(49,389)
Issuance of common stock and common stock equivalents in business combinations		1,504,811	32,074	1,472,737
Net shares issued under share-based compensation plans		(350)	351	(701)
Share-based compensation expense		13,452	6	13,446
Ending balance at Dec. 31, 2016		2,581,526	70,599	2,210,762	340,201	(40,036)
Changes in Stockholders' Equity
Cumulative effect adjustment of change in accounting policy, net of tax impact		3,659			3,659
Comprehensive income		168,579			149,523	19,056
Cash dividends declared		(78,498)			(78,498)
Issuance of common stock and common stock equivalents in business combinations		0	0	0
Net shares issued under share-based compensation plans		(23,863)	608	(24,471)
Share-based compensation expense		17,346	0	17,346
Reclassification of certain income tax effects	[1]	0			4,518	(4,518)
Ending balance at Dec. 31, 2017		$ 2,668,749	$ 71,207	$ 2,203,637	$ 419,403	$ (25,498)
[1]	The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, refer to Note 1 for further details on the adoption.

Consolidated Statements of Cha7

Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended											12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Cash dividends declared per share (in dollars per share)	$ 0.27	$ 0.28	$ 0.27	$ 0.27	$ 0.27	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.24	$ 0.24	$ 1.10	$ 1.06	$ 1

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net Income	$ 149,523	$ 108,032	$ 86,830
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	23,300	14,875	6,500
Gains on sales of loans	(31,734)	(15,686)	(6,354)
Proceeds from sales of loans	838,549	723,521	228,995
Loans originated for sale	(772,968)	(534,422)	(220,765)
Net losses (gains) on sale of investment securities	7,388	(129)	(630)
Net gains from sales/writedowns of other real estate and repossessed assets	(1,017)	(5,212)	(2,681)
Depreciation of premises and equipment	17,722	13,270	11,028
Amortization of intangible assets	6,090	10,046	8,444
Additions to loan servicing rights	(8,745)	(4,333)	(1,476)
Valuation change in loan servicing rights	8,880	(4,585)	(200)
Net amortization of premiums and discounts on investment securities	19,262	9,713	6,007
Share-based compensation expense	17,346	13,452	3,478
Deferred income tax expense	93,184	24,091	5,700
Net increase in interest receivable and other assets	(151,531)	(25,606)	(19,027)
Net increase (decrease) in interest payable and other liabilities	59,760	(46,449)	(2,800)
Net cash from operating activities	275,009	280,578	103,049
Investment securities — available-for-sale:
Proceeds from maturities, calls and principal reductions	318,952	248,772	212,051
Proceeds from sales and redemptions	409,220	41,446	40,301
Purchases	(1,480,524)	(187,702)	0
Investment securities — held-to-maturity:
Proceeds from maturities, calls and principal reductions	93,600	90,933	87,189
Purchases	(141,489)	(206,023)	(279,226)
Net increase in loans	(1,189,865)	(860,135)	(493,776)
Proceeds from sales of other real estate and repossessed assets	19,879	22,147	16,653
Purchases of premises and equipment, net of disposals	(12,852)	(18,098)	(8,527)
Cash acquired, net of cash paid, in business combinations	0	325,714	16,551
Net cash used in investing activities	(1,983,079)	(542,946)	(408,784)
Cash flows from financing activities
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	243,110	672,584	479,386
Net increase (decrease) in time deposits	526,571	(550,847)	(170,598)
Net increase (decrease) in securities sold under agreements to repurchase with customers and other short-term borrowings	1,247,189	401,144	(31,268)
Proceeds from issuance of long-term borrowings	0	375,000	125,000
Repayment of long-term borrowings	(224,850)	(351,018)	(6,000)
Cash dividends paid	(78,498)	(49,389)	(36,918)
Proceeds from directors' stock plans and exercise of stock options, net of shares withheld	3,991	1,572	2,473
Cash paid for payroll taxes upon conversion of share-based awards	(27,854)	(1,065)	(571)
Net cash from financing activities	1,689,659	497,981	361,504
Net increase (decrease) in cash and cash equivalents	(18,411)	235,613	55,769
Cash and cash equivalents at beginning of year	474,402	238,789	183,020
Cash and cash equivalents at end of year	455,991	474,402	238,789
Supplemental disclosures of cash flow information:
Interest paid	73,643	25,460	16,958
Net income tax payments	2,252	22,200	41,450
Non-cash activities:
Loans transferred to other real estate and repossessed assets	11,546	12,970	9,329
Net transfer of loans held-for-sale to loans held- for-investment	(4,150)	(289)	0
Closed branch offices transferred to other assets	13,246	4,846	2,692
Business combinations:
Fair value of tangible assets acquired (noncash)	420	6,371,781	1,282,420
Goodwill, loan servicing rights and other identifiable intangible assets acquired	1,034	908,217	118,744
Liabilities assumed	1,454	6,100,901	1,258,051
Common stock and stock options issued	$ 0	$ 1,504,811	$ 159,904

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Nature of Operations Chemical Financial Corporation ("Corporation" or "Chemical") operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within Michigan, Northeast Ohio and Northern Indiana as a Michigan state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of seven regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the Corporation's geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation's regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is generally uniform throughout the Corporation's regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products. The Corporation's primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts, wealth management revenue, net gain on sale of loans and other mortgage banking revenue. Basis of Presentation and Principles of Consolidation The accounting and reporting policies of the Corporation and its subsidiaries have been prepared in accordance with U.S. Generally Accepted Accounting Principles ("GAAP"), Securities and Exchange Commission ("SEC") rules and interpretive releases and prevailing practices within the banking industry. The Consolidated Financial Statements of the Corporation include the accounts of the Corporation and its wholly owned subsidiaries. All significant income and expenses are recorded on the accrual basis. Intercompany accounts and transactions have been eliminated in preparing the Consolidated Financial Statements. Use of Estimates Management makes estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, income and other taxes the valuation of loan servicing rights. Actual results could differ from these estimates. Business Combinations Pursuant to the guidance of the Financial Accounting Standards Board's ("FASB") Accounting Standards Codification ("ASC") Topic 805, Business Combinations ("ASC 805"), the Corporation recognizes assets acquired, including identified intangible assets, and the liabilities assumed in acquisitions at their fair values as of the acquisition date, with the acquisition-related transaction and restructuring costs expensed in the period incurred. See Note 2 for further information regarding the Corporation's mergers and acquisitions. Cash and Cash Equivalents For purposes of reporting cash flows, cash and cash equivalents include cash on hand and interest-bearing deposits held at the Federal Reserve Bank ("FRB"). Investment Securities Investment securities include investments in debt, trust preferred and preferred stock securities. Investment securities are accounted for in accordance with ASC Topic 320, Investments — Debt and Equity Securities ("ASC 320"), which requires investments to be classified within one of three categories (trading, held-to-maturity or available-for-sale). The Corporation held no trading investment securities at December 31, 2017 or 2016 . Designation as an investment security held-to-maturity is based on the Corporation's intent and ability to hold the security to maturity. Investment securities held-to-maturity are carried at amortized cost, adjusted for purchase price premiums and accretion of discounts. Investment securities that are not held-to-maturity are accounted for as securities available-for-sale, and are stated at estimated fair value, with the aggregate unrealized gains and losses classified as a component of accumulated other comprehensive income (loss), net of income taxes. Realized gains and losses on the sale of investment securities charges are determined using the specific identification method and are included within noninterest income in the Consolidated Statements of Income. Premiums and discounts on investment securities are amortized over the estimated lives of the related investment securities based on the effective interest yield method and are included in interest income in the Consolidated Statements of Income. The Corporation assesses equity and debt securities that have fair values below amortized cost basis to determine whether declines (impairment) are other-than-temporary. If the Corporation intends to sell an impaired security or it is more-likely-than-not that the Corporation will be required to sell an impaired security prior to the recovery of its amortized cost, an other-than-temporary impairment ("OTTI") write-down is recognized in earnings equal to the entire difference between the investment security's amortized cost basis and its fair value. In assessing whether OTTI exists, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, (iii) the potential for impairments in an entire industry or sub-sector and (iv) the potential for impairments in certain economically depressed geographical locations. For the years ended December 31, 2017 , 2016 and 2015 , the Corporation did not recognize OTTI. Nonmarketable Equity Securities The Corporation is required to hold non-marketable equity securities, comprised of Federal Home Loan Bank of Indianapolis ("FHLB") and FRB stock, as a condition of membership. These securities are accounted for at cost, which equals par or redemption value, and included in "interest receivable and other assets" on the Consolidated Statements of Financial Position. These securities do not have a readily determinable fair value as their ownership is restricted and there is no market for these securities. These securities can only be redeemed or sold at their par value and only to the respective issuing government supported institution or to another member institution. FHLB stock can only be redeemed upon giving a five year written notice and FRB stock can only be redeemed upon giving six months written notice, with no more than 25.0% eligible for redemption in any calendar year. The Corporation records these non-marketable equity securities as a component of other assets and they are periodically evaluated for impairment. Management considers these non-marketable equity securities to be long-term investments. Accordingly, when evaluating these securities for impairment, management considers the ultimate recoverability of the par value rather than recognizing temporary declines in value, if applicable. The estimated loss is recognized as a loss from equity investments in other noninterest income in the Consolidated Statements of Income. The Corporation's ownership of FHLB stock totaled $112.0 million at December 31, 2017 and $58.0 million at December 31, 2016 . The Corporation's ownership of FRB stock totaled $68.1 million at December 31, 2017 and $39.4 million at December 31, 2016 . Loans Held for Sale Mortgage and construction loans intended for sale in the secondary market are carried at fair value based on the Corporation's election of the fair value option. The estimated fair value of loans held for sale are based on quoted market prices for securities backed by similar types of loans, where available, or by discounting estimated cash flows using observable inputs inclusive of interest rates, prepayment speeds and loss assumptions for similar collateral. The fair value includes the servicing value of the loans as well as any accrued interest. These loans are sold both with servicing rights retained and with servicing rights released. Originated Loans Held for Investment Originated loans include the Corporation's entire portfolio loans held for investment, excluding loans acquired in business combinations, as further discussed below. Originated loans are stated at their principal amount outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Loan interest income is recognized on the accrual basis. Deferred loan fees and costs are amortized over the loan term based on the level-yield method. Net loan commitment fees are deferred and amortized into fee income on a straight-line basis over the commitment period. If a loan is transferred from the loan held for investment portfolio to the held for sale portfolio, any write-down in the carrying amount of the loan at the date of transfer is recorded as a charge-off. The loans are transferred at fair value determined using the same methods described above for held for sale loans. When loans classified as held for investment are transferred to loans held for sale due to a change in intent, cash flows associated with the loans will be classified in the Consolidated Statements of Cash Flows as operating or investing, as appropriate, in accordance with the initial classification of the loans. The past due status of a loan is based on the loan's contractual terms. A loan is placed in nonaccrual status (accrual of interest is discontinued) when principal or interest is past due 90 days or when doubt exists as to the ultimate collection of principal or interest, unless the loan is both well-secured and in the process of collection, or earlier when, in the opinion of management, there is sufficient reason to doubt the collectibility of principal or interest. Interest previously accrued, but not collected, is reversed and charged against interest income at the time the loan is placed in nonaccrual status. Subsequent receipts of interest while a loan is in nonaccrual status are recorded as a reduction of principal. Loans are returned to accrual status when principal and interest payments are brought current and are anticipated to be fully collectible, payments have been received consistently for a period of time (generally six months) and collectibility is no longer in doubt. Loans Acquired in a Business Combination Loans acquired in a business combination ("acquired loans") consist of loans acquired on August 31, 2016 in the merger with Talmer, on May 31, 2015 in the acquisition of Lake Michigan Financial Corporation ("Lake Michigan"), on April 1, 2015 in the acquisition of Monarch Community Bancorp, Inc. ("Monarch"), on October 31, 2014 in the acquisition of Northwestern Bancorp, Inc. ("Northwestern"), and on April 30, 2010 in the acquisition of O.A.K. Financial Corporation ("OAK"). Acquired loans were recorded at fair value at the date of acquisition, without a carryover of the associated allowance for loan losses related to these loans. The Corporation accounts for acquired loans, which are recorded at fair value at acquisition using an estimate of cash flows deemed to be collectible and an accretable yield, in accordance with ASC Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality ("ASC 310-30"). ASC 310-30 allows investors to aggregate loans acquired into loan pools that have common risk characteristics and thereby use a composite interest rate and expectation of cash flows expected to be collected for the loan pools. Under the provisions of ASC 310-30, the Corporation aggregated acquired loans into pools within each merger or acquisition based upon common risk characteristics, including types of loans, commercial type loans with similar risk grades and whether loans were performing or nonperforming. A pool is considered a single unit of accounting for the purposes of applying the guidance prescribed in ASC 310-30. A loan will be removed from a pool of acquired loans only if the loan is sold, foreclosed, paid off or written off, and will be removed from the pool at the carrying value. The estimate of expected credit losses was determined based on due diligence performed by executive and senior officers of the Corporation, with assistance from third-party consultants. The Corporation estimated the cash flows expected to be collected over the life of the pools of loans at acquisition and estimates expected cash flows quarterly thereafter, based on a set of assumptions including expectations as to default rates, prepayment rates and loss severities. The Corporation must make numerous assumptions, interpretations and judgments using internal and third-party credit quality information to determine whether it is probable that the Corporation will be able to collect all contractually required payments. This is a point in time assessment and inherently subjective due to the nature of the available information and judgment involved. The calculation of the fair value of the acquired loan pools entails estimating the amount and timing of cash flows attributable to both principal and interest expected to be collected on such loan pools and then discounting those cash flows at market interest rates. The excess of a loan pool's expected cash flows at the acquisition date over its estimated fair value is referred to as the "accretable yield," which is recognized into interest income over the estimated remaining life of the loan pool on a level-yield basis. The difference between a loan pool's contractually required principal and interest payments at the acquisition date and the cash flows expected to be collected at the acquisition date is referred to as the "nonaccretable difference," which includes an estimate of future credit losses expected to be incurred over the estimated life of the loan pool and interest payments that are not expected to be collected. Decreases to the expected cash flows in each loan pool in subsequent periods will require the Corporation to record a provision for loan losses and establish an allowance for loan loss. Improvements in expected cash flows in each loan pool in subsequent periods will result in reversing a portion of the nonaccretable difference, which is then classified as part of the accretable yield and subsequently recognized into interest income over the estimated remaining life of the loan pool. Loans Modified Under Troubled Debt Restructurings Loans modified under TDRs involve granting a concession to a borrower who is experiencing financial difficulty. Concessions generally include modifications to original loan terms, including changes to a loan's payment schedule, principal forgiveness, interest rate reductions, or other actions intended to minimize our economic loss and to avoid foreclosure or repossession of the collateral, if applicable, which generally would not otherwise be considered. The Corporation's TDRs include accruing TDRs, which consist of originated loans that continue to accrue interest as the Corporation expects to collect the remaining principal and interest on the loan, and nonaccrual TDRs, which include originated loans that are in a nonaccrual status and are no longer accruing interest, as the Corporation does not expect to collect the full amount of principal and interest owed from the borrower on these loans. All TDRs are accounted for as impaired loans and are included in the Corporation's analysis of the allowance for loan losses. A TDR that has been renewed by a borrower who is no longer experiencing financial difficulty and which yields a market rate of interest at the time of a renewal is no longer reported as a TDR, but only if they have been refinanced or restructured at market terms and qualify as a new loan. Loans in the Corporation's commercial loan portfolio (comprised of commercial, commercial real estate, real estate construction and land development loans) that meet the definition of a TDR generally consist of loans where the Corporation has allowed borrowers to defer scheduled principal payments and make interest-only payments for a specified period of time at the stated interest rate of the original loan agreement or reduced payments due to a moderate extension of the loan's contractual term. If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR and impairment is measured based on collateral values, if the loan is collateral dependent. If the Corporation does not expect to incur a loss on the loan based on its assessment of the borrowers' expected cash flows, as the pre- and post-modification effective yields are approximately the same, the loan is current and a six-month payment history has been sustained, the loan is classified as an accruing TDR. Since no loss is expected to be incurred on these loans, no additional provision for loan losses has been recognized for these loans and they continue to accrue interest at their contractual interest rate. Accruing TDRs are transferred to nonaccrual status if they become 90 days past due as to principal or interest payments or if it is probable that any remaining principal and interest payments due on the loan will not be collected in accordance with the modified terms of the loan. If accruing TDRs are deemed to be collateral dependent, they are measured based on collateral values. Loans in the Corporation's consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a TDR include a concession that reduces a borrower's monthly payments by decreasing the interest rate charged on the loan for a specified period of time (generally 24 months) under a formal modification agreement. The Corporation recognizes an additional provision for loan losses related to impairment on these loans on an individual basis based on the present value of expected future cash flows discounted at the loan's original effective interest rate. These loans continue to accrue interest at their effective interest rate, which consists of contractual interest under the terms of the modification agreement in addition to an adjustment for the accretion of computed impairment. TDRs are placed on nonaccrual status if they become 90 days past due as to principal or interest payments, or sooner if conditions warrant and measure impairment based on collateral values, if the loan is collateral dependent. Impaired Loans Impaired loans include loans on nonaccrual status and TDRs. Loans are considered impaired when based on current information and events it is probable the Corporation will be unable to collect all amounts due in accordance with the original contractual terms of the loan agreements. Impaired loans are accounted for at the lower of the present value of expected cash flows discounted at the loan's original effective interest rate or the estimated fair value of the collateral, if the loan is collateral dependent. When the present value of expected cash flows or the fair value of collateral of an impaired loan in the originated loan portfolio is less than the amount of unpaid principal outstanding on the loan, the principal balance of the loan is reduced to its carrying value through either a specific allowance for loan losses or a partial charge-off of the loan balance. Nonperforming Loans Nonperforming loans are comprised of loans for which the accrual of interest has been discontinued (nonaccrual loans, including nonaccrual TDRs). Acquired loans that were classified as nonperforming loans prior to being acquired and acquired loans that are not performing in accordance with contractual terms subsequent to acquisition are not classified as nonperforming loans subsequent to acquisition because the loans are recorded in pools at net realizable value based on the principal and interest the Corporation expects to collect on such loans. They continue to earn interest from accretable yield, independent of performance in accordance of their contractual terms, and are expected to be fully collected under the new carrying values of such loans (that is, the new cost basis arising out of purchase accounting). Allowance for Loan Losses The allowance for credit losses ("allowance") consists of two components: the allowance for loan losses (including both the originated and acquired loan portfolios) and the reserve for unfunded credit commitments. Unfunded credit commitments include items such as letters of credit, financial guarantees and binding unfunded loan commitments. The allowance represents management’s estimate of probable credit losses inherent in the loan and credit commitment portfolios as of period end. The allowance is calculated with the objective of maintaining a reserve sufficient to absorb losses inherent in the loan portfolio. The determination of the amount of the allowance requires significant judgment and the use of estimates related to the amount and timing of expected cash flows on acquired loans and impaired loans, collateral values on impaired loans, and estimated losses on pools of homogeneous loans based on historical loss experience, and consideration of current economic trends and conditions, all of which may be susceptible to significant change. The principal assumption used in deriving the allowance is the estimate of a loss percentage for each type of loan. In determining the allowance for the originated loan portfolio and the related provision for loan losses, the Corporation considers three principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans, (ii) reserves, by loan classes, on all other loans based on a six-year historical loan loss experience, loan loss trends and giving consideration to estimated loss emergence periods, and (iii) a reserve for qualitative factors that take into consideration risks inherent in the originated loan portfolio that differ from historical loan loss experience. The first element reflects the Corporation's estimate of probable losses based upon the systematic review of individually impaired loans in the originated loan portfolio. These estimates are based upon a number of objective factors, such as payment history, financial condition of the borrower and discounted collateral exposure. The Corporation measures the investment in an impaired loan based on one of three methods: the loan's observable market price; the fair value of the collateral; or the present value of expected future cash flows discounted at the loan's effective interest rate. Loans in the commercial loan portfolio that were in nonaccrual status (including nonaccrual TDRs) were valued based on the fair value of the collateral securing the loan, while accruing TDRs in the commercial loan portfolio and consumer loans were valued based on the present value of expected future cash flows discounted at the loan's effective interest rate. It is the Corporation's general policy to obtain new appraisals at initial impairment and updated when deemed necessary on nonaccrual loans in the commercial loan portfolio. Appraisals on nonaccrual loans in the consumer loan portfolio are updated at initial impairment and when deemed necessary where there is a delay in the foreclosure process. When the Corporation determines that the fair value of the collateral is less than the carrying value of an impaired loan and a portion is deemed not collectible, the portion of the impairment that is deemed not collectible is charged off (confirmed loss) and deducted from the allowance. The remaining carrying value of the impaired loan is classified as a nonperforming loan. When the Corporation determines that the fair value of the collateral is less than the carrying value of an impaired loan but believes it is probable it will recover this impairment, the Corporation establishes a valuation allowance for such impairment. The second element is determined by assigning allocations based principally upon a six -year average of loss experience for each class of loan. Average losses may be adjusted based on current loan loss experience, delinquency trends, estimated loss emergence periods and other industry specific environmental factors. This component considers the lagging impact of historical charge-off ratios in periods where future loan charge-offs are expected to increase or decrease, trends in delinquencies and nonaccrual loans, the changing portfolio mix in terms of collateral, average loan balance, loan growth and the degree of seasoning in the various loan portfolios. Loan loss analyses are performed quarterly and certain inputs and parameters are updated as necessary to reflect the current credit environment. The third element is based on qualitative factors that cannot be associated with a specific credit or loan class and reflects an attempt to ensure that the overall allowance appropriately reflects additional losses that are inherent in the Corporation's loan portfolio. Determination of the probable losses inherent in the portfolio, which are not necessarily captured by the allocation methodology discussed above, involves the exercise of judgment. This qualitative portion of the allowance is judgmentally determined and generally serves to compensate for the uncertainty in estimating inherent losses, particularly in times of changing economic conditions, and also considers the inherent judgment associated with risk rating commercial loans. The qualitative portion of the allowance also takes into consideration, among other things, economic conditions within our geographic areas and nationwide, including unemployment levels, industry-wide and Corporation specific loan delinquency rates, changes in composition of and growth in the Corporation's loan portfolio and changing commercial and residential real estate values. Consumer loans secured by real estate are charged-off to the estimated fair value of the collateral when a loss is confirmed or at 180 days past due, whichever is sooner. Loss confirming events include, but are not limited to, bankruptcy (unsecured), continued delinquency, foreclosure or receipt of an asset valuation indicating a collateral deficiency and the asset is the sole source of repayment. For consumer loans not secured by real estate, the charge-off is taken upon confirmation or 120 days past due. Commercial loans are evaluated on a loan level basis and either charged-off or written down to net realizable value if a loss confirming event has occurred. Loss confirming events include, but are not limited to, bankruptcy (unsecured), continued delinquency, foreclosure, or receipt of an asset valuation indicating a collateral deficiency and that asset is the sole source of repayment. Although the Corporation allocates portions of the allowance to specific loans and loan types, the entire allowance attributable to originated loans is available for any loan losses that occur in the originated portfolio. Loans that are deemed not collectible are charged off and reduce the allowance. The provision for loan losses and recoveries on loans previously charged off increase the allowance. Collection efforts may continue and recoveries may occur after a loan is charged off. Acquired loans are aggregated into pools based upon common risk characteristics. An allowance may be recorded related to an acquired loan pool if it experiences a decrease in expected cash flows, as compared to those projected at the acquisition date. On a quarterly basis, the expected future cash flow of each pool is estimated based on various factors, including changes in property values of collateral dependent loans, default rates, loss severities and prepayment speeds. Decreases in estimates of expected cash flows within a pool generally result in a charge to the provision for loan losses and a corresponding increase in the allowance allocated to acquired loans for the particular pool. Increases in estimates of expected cash flows within a pool generally result in a reduction in the allowance allocated to acquired loans for the particular pool, if applicable, and then an adjustment to the accretable yield for the pool, which will increase amounts recognized in interest income in subsequent periods. Various regulatory agencies, as an integral part of their examination processes, periodically review the allowance. Such agencies may require additions to the allowance, based on their judgment, reflecting information available to them at the time of their examinations. Mortgage Banking Operations The Corporation generally sells conforming long-term fixed interest rate mortgage loans it originates in the secondary market. Gains on the sales of these loans are determined using the specific identification method. The Corporation sells residential mortgage loans in the secondary market on either a servicing retained or released basis. The Corporation elected the fair value measurement option, as prescribed by ASC Topic 820, Fair Value Measurements and Disclosures ("ASC 820"), for all residential mortgage loans held-for-sale originated on or after July 1, 2012. This election allows for a more effective offset of the changes in fair value of residential mortgage loans held-for-sale and the derivative instruments used to economically hedge them without having to apply complex hedge accounting provisions. Residential mortgage loans held-for-sale are carried at fair value, with changes in fair value recorded through earnings. Residential mortgage loan commitments, forward commitments, are generally entered into at the time customer applications are accepted to protect the value of the mortgage loans from increases in market interest rates during the period held and are generally settled with the investor in the secondary market within 90 days after entering into the forward commitment. Forward loan commitments are accounted for as derivatives and recorded at fair value, with changes in fair value recorded through earnings. The Corporation recognizes revenue associated with the expected future cash flows of servicing loans for loans held-for-sale at the time a forward loan commitment is made to originate a held-for-sale loan, as required under SEC Staff Accounting Bulletin No. 109, Written Loan Commitments Recorded at Fair Value through Earnings. The Corporation purchases and originates loans for sale to the secondary market and sell the loans on either a servicing retained or servicing-released basis. If we retain the right to service the loan, a loan servicing rights ("LSRs") is created at the time of sale which is recorded at fair value. Effective January 1, 2017, the Corporation elected to account for all LSRs previously accounted for under the lower of cost or fair value method under the fair value method. Management believes this election will provide more comparable results to peers as many of those within our industry group account for loan servicing rights under the fair value method. The change in accounting policy in the first quarter of 2017 resulted in a cumulative adjustment to increase retained earnings in the amount of $3.7 million , net of taxes. LSRs are established and recorded at the estimated fair value by calculating the present fair value of estimated future net servicing cash flows. To determine the fair value of LSRs, the Corporation uses an independent third party valuation model requiring the incorporation of assumptions that market participants would use in estimating future net servicing income, which include estimates of prepayment speeds, discount rate, cost to service and escrow account earnings. Changes in the fair value of LSRs directly impact earnings. Servicing income is recognized in net gain on sale of loans and other mortgage banking revenue in the Consolidated Statements of Income when earned and is offset by the fair value of LSRs. Derivatives The Corporation enters into derivative to manage the fair value changes, exposure to fluctuations exposed to price and interest rate risk, facilitate asset/liability management, minimize the variability of future cash flows on long-term debt, and to provide a service to certain qualifying customers to help facilitate their respective risk management strategies ("customer-initiated derivatives"). All derivatives are recognized on the Consolidated Statements of Financial Condition as other

Mergers and Acquisitions

Mergers and Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Mergers and Acquisitions	Mergers and Acquisitions Merger with Talmer Bancorp, Inc. On August 31, 2016, the Corporation completed the merger with Talmer for total consideration of $1.61 billion . As a result of the merger, the Corporation issued 32.1 million shares of its common stock based on an exchange ratio where each Talmer shareholder received 0.4725 shares of the Corporation's common stock, and $ 1.61 in cash, for each share of Talmer common stock. In conjunction with the merger, the Corporation entered into and drew on a $125.0 million credit facility, which is described in more detail in Note 15. The proceeds from the credit facility were used to pay off the Corporation's $25.0 million line-of-credit and a $ 37.5 million line-of-credit of Talmer, with the remaining proceeds used to partially fund the cash portion of the merger consideration. The Corporation incurred $8.5 million and $61.1 million of merger and acquisition-related transaction expenses during the years ended December 31, 2017 and 2016 , respectively. As a result of the merger, Talmer Bank and Trust became a wholly-owned subsidiary of the Corporation. Talmer Bank and Trust was consolidated with and into Chemical Bank during the fourth quarter of 2016. The Company determined that the merger with Talmer constitutes a business combination as defined by ASC 805. Accordingly, the assets acquired and liabilities assumed were recorded at their fair values on the date of acquisition. Fair values were determined in accordance with the guidance provided in ASC Topic 820, Fair Value Measurements, as of the merger date as presented in the following table. (Dollars in thousands) Consideration paid: Stock $ 1,504,811 Cash 107,638 Total consideration 1,612,449 Fair value of identifiable assets acquired (1) : Cash and cash equivalents 433,352 Investment securities: Available-for-sale 808,894 Held-to-maturity 1,657 Loans held-for-sale 244,916 Loans 4,882,402 Premises and equipment 38,793 Loan servicing rights 42,462 Other intangible assets 19,088 Interest receivable and other assets (2) 395,539 Total identifiable assets acquired 6,867,103 Fair value of liabilities assumed (1) : Noninterest-bearing deposits 1,236,902 Interest-bearing deposits 4,057,716 Interest payable and other liabilities (2) 100,936 Securities sold under agreements to repurchase with customers 19,704 Short-term borrowings 387,500 Long-term borrowings 299,597 Total liabilities assumed 6,102,355 Fair value of net identifiable assets acquired 764,748 Goodwill resulting from acquisition (2) $ 847,701 (1) All amounts were previously reported in the Corporation's Annual Report on Form 10-K for the year ended December 31, 2016, with the exception of interest receivable and other assets and interest payable and other liabilities. (2) Includes adjustments to the fair value as a result of additional valuation information obtained during the third quarter of 2017, including the corresponding tax effects. During the third quarter of 2017, prior to August 31, 2017, additional valuation information was obtained related to the fair value of certain liabilities and deferred tax assets, which resulted in an adjustment to goodwill acquired in the Talmer transaction. The adjustment recorded during the third quarter of 2017 resulted in a $1.0 million increase to the amount of goodwill recorded for the Talmer transaction. Information regarding loans accounted for under ASC 310-30 at the merger date is as follows: (Dollars in thousands) Accounted for under ASC 310-30: Contractual cash flows $ 5,968,488 Contractual cash flows not expected to be collected (nonaccretable difference) 223,959 Expected cash flows 5,744,529 Interest component of expected cash flows (accretable yield) 862,127 Fair value at acquisition $ 4,882,402 Acquisition of Lake Michigan Financial Corporation On May 31, 2015, the Corporation acquired all of the outstanding stock of Lake Michigan Financial Corporation (Lake Michigan) for total consideration of $187.4 million , which included stock consideration of $132.9 million and cash consideration of $54.5 million . As a result of the acquisition, the Corporation issued approximately 4.3 million shares of its common stock, based on an exchange ratio of 1.326 shares of its common stock, and paid $16.64 in cash, for each share of Lake Michigan common stock outstanding. Lake Michigan, a bank holding company which owned The Bank of Holland and The Bank of Northern Michigan, provided traditional banking services and products with five banking offices in Holland, Grand Haven, Grand Rapids, Petoskey and Traverse City, Michigan. The Bank of Holland and the Bank of Northern Michigan were consolidated with and into Chemical Bank on November 13, 2015. At the acquisition date, Lake Michigan added total assets of $1.24 billion , including total loans of $985.5 million , and total deposits of $924.7 million to the Consolidated Statement of Financial Position. The Corporation recorded $101.1 million of goodwill, which was primarily attributable to the synergies and economies of scale expected from combining the operations of the Corporation and Lake Michigan. In addition, the Corporation recorded $8.6 million of core deposit and other intangible assets in conjunction with the acquisition. The results of the merged Lake Michigan operations are presented in the Consolidated Financial Statements from the date of acquisition. Acquisition-related expenses associated with the Lake Michigan transaction totaled $5.5 million during 2015. The summary computation of the purchase price, including adjustments to reflect Lake Michigan's assets acquired and liabilities assumed at fair value and the allocation of the purchase price to the net assets of Lake Michigan, is presented below. (Dollars in thousands) Stock $ 132,916 Cash 54,478 Total consideration 187,394 Net assets acquired: Lake Michigan shareholders' equity $ 89,280 Adjustments to reflect fair value of net assets acquired: Loans (22,600 ) Allowance for loan losses 15,888 Premises and equipment (5,031 ) Core deposit intangibles 8,003 Deferred tax assets, net 4,096 Deposits and borrowings, net (3,182 ) Other assets and other liabilities (121 ) Fair value of adjusted net assets acquired 86,333 Goodwill recognized as a result of the Lake Michigan transaction $ 101,061 Allocation of Purchase Price The following schedule summarizes the acquisition date fair values of assets acquired and liabilities assumed from Lake Michigan: (Dollars in thousands) Assets Cash and cash equivalents $ 39,301 Investment securities 66,699 Loans 985,542 Premises and equipment 10,975 Deferred tax asset, net 16,715 Goodwill 101,061 Core deposit intangible asset 8,003 Bank-owned life insurance 23,844 Other assets 37,695 Assets acquired, at fair value 1,289,835 Liabilities Deposits 924,697 Short-term borrowings 30,000 Other borrowings 124,857 Other liabilities 22,887 Total liabilities acquired, at fair value 1,102,441 Total purchase price $ 187,394 Information regarding loans accounted for under ASC 310-30 at the merger date is as follows: (Dollars in thousands) Accounted for under ASC 310-30: Contractual cash flows $ 1,198,388 Contractual cash flows not expected to be collected (nonaccretable difference) 22,600 Expected cash flows 1,175,788 Interest component of expected cash flows (accretable yield) 190,246 Fair value at acquisition $ 985,542 Acquisition of Monarch Community Bancorp, Inc. On April 1, 2015, the Corporation acquired all of the outstanding stock of Monarch Community Bancorp, Inc. (Monarch) in an all-stock transaction valued at $27.2 million . As a result of the acquisition, the Corporation issued 860,575 shares of its common stock based on an exchange ratio of 0.0982 shares of its common stock for each share of Monarch common stock outstanding. Monarch, a bank holding company, owned Monarch Community Bank, which operated five full service branch offices in Coldwater, Marshall, Hillsdale and Union City, Michigan. Monarch Community Bank was consolidated with and into Chemical Bank on May 8, 2015. At the acquisition date, Monarch added total assets of $182.8 million , including total loans of $121.8 million , and total deposits of $144.3 million to the Consolidated Statement of Financial Position. In connection with the acquisition of Monarch, the Corporation recorded $5.3 million of goodwill, which was primarily attributable to the synergies and economies of scale expected from combining the operations of the Corporation and Monarch. In addition, the Corporation recorded $1.9 million of core deposit intangible assets in conjunction with the acquisition. The results of the merged Monarch operations are presented in the Consolidated Financial Statements from the date of acquisition. The disclosure of Monarch's post-acquisition revenue and net income is not practical due to the combining of Monarch's operations with and into Chemical Bank during the second quarter of 2015. Acquisition-related expenses associated with the Monarch transaction totaled $2.3 million during 2015. The summary computation of the purchase price, including adjustments to reflect Monarch's assets acquired and liabilities assumed at fair value and the allocation of the purchase price to the net assets of Monarch is presented below. (Dollars in thousands) Stock $ 26,988 Cash 203 Total consideration $ 27,191 Net assets acquired: Monarch shareholders' equity $ 15,270 Adjustments to reflect fair value of net assets acquired: Loans (7,150 ) Allowance for loan losses 2,128 Deferred tax assets, net: Net operating loss carryforward 7,900 Other 1,826 Premises and equipment (415 ) Core deposit intangibles 1,930 Mortgage servicing rights 315 Other assets and other liabilities 48 Fair value of adjusted net assets acquired 21,852 Goodwill recognized as a result of the Monarch transaction $ 5,339 Allocation of Purchase Price The following schedule summarizes the revised acquisition date estimated fair values, including the adjustments to the fair values identified and recorded from the acquisition date through December 31, 2015, of assets acquired and liabilities assumed from Monarch. (Dollars in thousands) Assets Cash and cash equivalents $ 32,171 Loans 121,783 Premises and equipment 3,019 Deferred tax assets, net Net operating loss carryforward 7,900 Other 2,392 Interest receivable and other assets 6,972 Goodwill 5,339 Core deposit intangibles 1,930 Mortgage servicing rights 1,284 Assets acquired, at fair value 182,790 Liabilities Deposits 144,300 FHLB advances 8,000 Interest payable and other liabilities 3,299 Total liabilities acquired, at fair value 155,599 Total purchase price $ 27,191 Information regarding loans accounted for under ASC 310-30 at the merger date is as follows: (Dollars in thousands) Accounted for under ASC 310-30: Contractual cash flows $ 166,797 Contractual cash flows not expected to be collected (nonaccretable difference) 7,100 Expected cash flows 159,697 Interest component of expected cash flows (accretable yield) 37,914 Fair value at acquisition $ 121,783 The outstanding contractual principal balance and the carrying amount of the Monarch acquired loan portfolio were $ 76.0 million and $ 70.8 million , respectively, at December 31, 2017 , compared to $92.4 million and $86.4 million , respectively, at December 31, 2016 . Unaudited Pro Forma Combined Results of Operations The following unaudited pro forma financial information presents the consolidated results of operation of the Corporation and Talmer as if the merger had occurred as of January 1, 2015 and Lake Michigan and Monarch as if the acquisitions had occurred as of January 1, 2014. The unaudited pro forma combined results of operations are presented solely for information purposes and are not intended to represent or be indicative of the consolidated results of operations that Chemical would have reported had these transactions been completed as of the dates and for the periods presented, nor are they necessarily indicative of future results. In particular, no adjustments have been made to eliminate the amount of Talmer's, Lake Michigan's or Monarch's provision for loan losses incurred prior to the acquisition date that would not have been necessary had the acquired loans been recorded at fair value as of the beginning of each period indicated. In accordance with Article 11 of SEC Regulation S-X, transaction costs directly attributable to the acquisitions have been excluded. Years ended December 31, (In thousands, except per share data) 2017 2016 2015 Net interest and other income $ 701,597 $ 492,323 $ 654,962 Net Income 149,523 115,847 142,504 Earnings per share: Basic $ 2.11 $ 1.65 $ 2.03 Diluted $ 2.08 $ 1.62 $ 2.01

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value, as defined by GAAP, is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. A fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability. The price in the principal (or most advantageous) market used to measure the fair value of the asset or liability is not adjusted for transaction costs. An orderly transaction is a transaction that assumes exposure to the market for a period prior to the measurement date to allow for market activities that are usual and customary for transactions involving such assets and liabilities; it is not a forced transaction. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact and (iv) willing to transact. The Corporation utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures. Investment securities — available-for-sale, loans held-for-sale, loan servicing rights and derivatives are recorded at fair value on a recurring basis. Additionally, the Corporation may be required to record other assets, such as impaired loans, goodwill, other intangible assets, other real estate and repossessed assets, at fair value on a nonrecurring basis. These nonrecurring fair value adjustments typically involve the application of lower of cost or market accounting or write-downs of individual assets. The Corporation determines the fair value of its financial instruments based on a three-level hierarchy established by GAAP. The classification and disclosure of assets and liabilities within the hierarchy is based on whether the inputs to the valuation methodology used for measurement are observable or unobservable. Observable inputs reflect market-derived or market-based information obtained from independent sources, while unobservable inputs reflect management's estimates about market data. The three levels of inputs that may be used to measure fair value within the GAAP hierarchy are as follows: Level 1 Valuation is based upon quoted prices for identical instruments traded in active markets. Level 1 valuations for the Corporation include U.S. Treasury securities that are traded by dealers or brokers in active over-the-counter markets. Valuations are obtained from a third-party pricing service for these investment securities. Level 2 Valuation is based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant assumptions are observable in the market. Level 2 valuations for the Corporation include government sponsored agency securities, including securities issued by the Federal Home Loan Bank, Federal Home Loan Mortgage Corporation, Federal National Mortgage Association, Federal Farm Credit Bank, Student Loan Marketing Corporation and the Small Business Administration, securities issued by certain state and political subdivisions, residential mortgage-backed securities, collateralized mortgage obligations, corporate bonds, preferred stock and available-for-sale trust preferred securities. Valuations are obtained from a third-party pricing service for these investment securities. Additionally included in Level 2 valuations are loans held-for-sale and derivative assets and liabilities. Level 3 Valuation is generated from model-based techniques that use at least one significant assumption not observable in the market. These unobservable assumptions reflect estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include use of option pricing models, discounted cash flow models, yield curves and similar techniques. The determination of fair value requires management judgment or estimation and generally is corroborated by external data, which includes third-party pricing services. Level 3 valuations for the Corporation include securities issued by certain state and political subdivisions, held-to-maturity trust preferred investment securities, impaired loans, goodwill, core deposit intangible assets, non-compete intangible assets, LSRs and other real estate and repossessed assets. A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. These valuation methodologies were applied to all of the Corporation's financial assets and financial liabilities carried at fair value and all financial instruments disclosed at fair value. Transfers of asset or liabilities between levels of the fair value hierarchy are recognized at the beginning of the reporting period, when applicable. In general, fair value is based upon quoted market prices, where available. If quoted market prices are not available, fair value is based upon third-party pricing services when available. Fair value may also be based on internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be required to record financial instruments at fair value. Any such valuation adjustments are applied consistently over time. The Corporation's valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. While management believes the Corporation's valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Furthermore, the fair value amounts may change significantly after the date of the statement of financial position from the amounts reported in the Consolidated Financial Statements and related notes. Assets and Liabilities Recorded at Fair Value on a Recurring Basis Investment securities: Investment securities classified as available-for-sale are recorded at fair value on a recurring basis. Fair value measurement is based upon quoted prices, if available. If quoted prices are not available, fair values are generally measured using independent pricing models or other model-based valuation techniques that include market inputs, such as benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data and industry and economic events. Loans held-for-sale: The Corporation has elected the fair value option for all loans held-for-sale. Accordingly, loans held-for-sale are recorded at fair value on a recurring basis. The fair values of loans held-for-sale are based on the market price for similar loans sold in the secondary market, and therefore, are classified as Level 2 valuations. Loan servicing rights: Effective January 1, 2017, the Corporation elected to account for all LSRs under the fair value measurement method. LSRs acquired related to the merger with Talmer effective August 31, 2016 were also previously accounted for under the fair value measurement method based on accounting election. A third party valuation model is used to determine the fair value at the end of each reporting period utilizing a discounted cash flow analysis using interest rates and prepayment speed assumptions currently quoted for comparable instruments and a discount rate determined by management. Because of the nature of the valuation inputs, the Corporation classifies loan servicing rights as Level 3. Refer to Note 9, “Loan Servicing Rights”, for the assumptions included in the valuation of loan servicing rights. Derivatives: The Corporation enters into interest rate lock commitments with prospective borrowers to be sold into the secondary market and forward commitments for the future delivery of mortgage loans to third party investors, which are carried at fair value on a recurring basis. The fair value of these commitments is based on the fair value of related mortgage loans determined using observable market data. Interest rate lock commitments are adjusted for expectations of exercise and funding. This adjustment is not considered to be a material input. The Corporation classifies interest rate lock commitments and forward contracts related to mortgage loans to be delivered for sale as recurring Level 2. Derivative instruments held or issued for risk management or customer-initiated activities are traded in over-the counter markets where quoted market prices are not readily available. Fair value for over-the-counter derivative instruments is measured on a recurring basis using third party models that use primarily market observable inputs, such as yield curves and option volatilities. The fair value for these derivatives may include a credit valuation adjustment that is determined by applying a credit spread for the counterparty or the Corporation, as appropriate, to the total expected exposure of the derivative after considering collateral and other master netting arrangements. These adjustments, which are considered Level 3 inputs, are based on estimates of current credit spreads to evaluate the likelihood of default. The Corporation assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions at both December 31, 2017 and 2016 and it was determined that the credit valuation adjustments were not significant to the overall valuation of its derivatives. As a result, the Corporation classifies its risk management interest rate swaps designated as cash flow hedges and customer-initiated derivatives valuations in Level 2 of the fair value hierarchy. Foreign exchange forward and option contracts are entered into primarily to accommodate the needs of the customer. These derivatives are not designated as hedging. Fair value of foreign exchange forward and option contracts are measured on a recurring basis using third party models that use primarily market observable inputs, such as yield curves and option volatilities. The Corporation classifies its foreign exchange forward and option contracts in Level 2 of the fair value hierarchy. Written and purchased option derivatives consist of instruments to facilitate an equity-linked time deposit product (the "Power Equity CD"). The Power Equity CD is a time deposit that provides the purchaser a guaranteed return of principal at maturity plus a potential equity return, while the Corporation receives a known stream of funds based on equity returns. The written and purchased options are mirror derivative instruments which are carried at fair value on the Consolidated Statements of Financial Position. Fair value measurements for the Power Equity CD are determined using quoted prices of underlying stocks, along with other terms and features of the derivative instrument. As a result, the Power Equity CD derivatives are classified as Level 2 valuations. Disclosure of Recurring Basis Fair Value Measurements For assets and liabilities measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets and liabilities follow: (Dollars in thousands) Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total December 31, 2017 Investment securities — available-for-sale: Government sponsored agencies $ — $ 202,916 $ — $ 202,916 State and political subdivisions — 345,970 — 345,970 Mortgage-backed securities — 150,131 — 150,131 Collateralized mortgage obligations — 1,033,845 — 1,033,845 Corporate bonds — 192,794 — 192,794 Preferred stock and trust preferred securities — 37,890 — 37,890 Total investment securities — available-for-sale — 1,963,546 — 1,963,546 Loans held-for-sale — 52,133 — 52,133 Loan servicing rights — — 63,841 63,841 Derivative assets: Customer-initiated derivatives — 9,376 — 9,376 Interest rate lock commitments — 1,222 — 1,222 Power Equity CD — 2,184 — 2,184 Risk management derivatives — 5,899 — 5,899 Total derivatives — 18,681 — 18,681 Total assets at fair value $ — $ 2,034,360 $ 63,841 $ 2,098,201 Derivative liabilities: Customer-initiated derivatives $ — $ 10,139 $ — $ 10,139 Forward contracts related to mortgage loans to be delivered for sale — 34 — 34 Power Equity CD — 2,184 — 2,184 Total derivatives — 12,357 — 12,357 Total liabilities at fair value $ — $ 12,357 $ — $ 12,357 (Dollars in thousands) Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total December 31, 2016 Investment securities — available-for-sale: U.S. Treasury securities $ 5,793 $ — $ — $ 5,793 Government sponsored agencies — 215,011 — 215,011 State and political subdivisions — 300,088 — 300,088 Residential mortgage-backed securities — 272,282 — 272,282 Collateralized mortgage obligations — 320,025 — 320,025 Corporate bonds — 89,474 — 89,474 Preferred stock and trust preferred securities — 32,291 — 32,291 Total investment securities — available-for-sale 5,793 1,229,171 — 1,234,964 Loans held-for-sale — 81,830 — 81,830 Loan servicing rights — — 48,085 48,085 Derivative assets: Customer-initiated derivatives — 4,406 — 4,406 Forward contracts related to mortgage loans to be delivered for sale — 635 — 635 Interest rate lock commitments — 956 — 956 Power Equity CD — 2,218 — 2,218 Total derivatives — 8,215 — 8,215 Total assets at fair value $ 5,793 $ 1,319,216 $ 48,085 $ 1,373,094 Derivative liabilities: Customer-initiated derivatives — 4,141 — 4,141 Power Equity CD — 2,218 — 2,218 Total derivatives — 6,359 — 6,359 Total liabilities at fair value $ — $ 6,359 $ — $ 6,359 There were no transfers between levels within the fair value hierarchy during the year ended December 31, 2017 . The following table summarizes the changes in Level 3 assets measured at fair value on a recurring basis. Year Ended December 31, 2017 2016 (Dollars in thousands) Loan servicing rights Balance, beginning of period $ 48,085 $ — Additions due to acquisition — 42,462 Transfer in based on new accounting policy election (1) 15,891 — Gains (losses): Recorded in earnings (realized): Recorded in "Net gain on sale of loans and other mortgage banking revenue" (8,880 ) 4,593 New originations 8,745 1,030 Balance, end of period $ 63,841 $ 48,085 (1) Refer to Note 1, Basis of Presentation and Significant Accounting Policies, for further details. The Corporation has elected the fair value option for loans held-for-sale. These loans are intended for sale and the Corporation believes that the fair value is the best indicator of the resolution of these loans. Interest income is recorded based on the contractual terms of the loans in accordance with the Corporation's policy on loans held for investment in “Interest and fees on loans” in the Consolidated Statements of Income. There were no loans held-for-sale that were on nonaccrual status or 90 days past due and on accrual status as of December 31, 2017 and 2016 . The aggregate fair value, contractual balance (including accrued interest), and gain or loss for loans held-for-sale carried at fair value option was as follows: December 31, (Dollars in thousands) 2017 2016 Aggregate fair value $ 52,133 $ 81,830 Contractual balance 50,597 81,009 Unrealized gain (loss) 1,536 821 The total amount of gains (losses) from loans held-for-sale included in the Consolidated Statements of Income was as follows: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Interest income (1) $ 2,540 $ 1,606 $ 83 Change in fair value (2) 715 39 (61 ) Net gain on sales of loans (2) 31,734 15,686 6,354 Total included in earnings $ 34,989 $ 17,331 $ 6,376 (1) Included in "Interest and fees on loans" in the Consolidated Statements of Income. (2) Included in "Net gain on sale of loans and other mortgage banking revenue" in the Consolidated Statements of Income. Assets and Liabilities Recorded at Fair Value on a Nonrecurring Basis Investment securities : Investment securities classified as held to maturity are recorded at fair value if the value is below amortized cost and the Corporation has determined that such unrealized loss is an other-than-temporary impairment. Fair value measurement is based upon quoted prices, if available. If quoted prices are not available, fair values are generally measured using independent pricing models or other model-based valuation techniques that include market inputs, such as benchmark yields, reported trades, broker dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data and industry and economic events. Impaired Loans: The Corporation does not record loans held for investment at fair value on a recurring basis. However, from time to time, a loan is considered impaired and an allocation of the allowance (valuation allowance) may be established or a portion of the loan is charged off. Loans for which it is probable that payment of interest and principal will not be made in accordance with the contractual terms of the loan agreement are considered impaired. The fair value of impaired loans is estimated using one of several methods, including the loan's observable market price, the fair value of the collateral or the present value of the expected future cash flows discounted at the loan's effective interest rate. Those impaired loans not requiring a valuation allowance represent loans for which the fair value of the expected repayments or collateral exceed the remaining carrying amount of such loans. Impaired loans where a valuation allowance is established or a portion of the loan is charged off based on the fair value of collateral are subject to nonrecurring fair value measurement and require classification in the fair value hierarchy. The Corporation records impaired loans as Level 3 valuations as there is generally no observable market price or management determines the fair value of the collateral is further impaired below the independent appraised value. When management determines the fair value of the collateral is further impaired below the appraised value, discounts ranging between 20% and 30% of the appraised value are used depending on the nature of the collateral and the age of the most recent appraisal. Goodwill: Goodwill is subject to impairment testing on an annual basis. The assessment of goodwill for impairment requires a significant degree of judgment. In the event the assessment indicates that it is more-likely-than-not that the fair value is less than the carrying value, the asset is considered impaired and recorded at fair value. Goodwill that is impaired and subject to nonrecurring fair value measurements is a Level 3 valuation. At December 31, 2017 and 2016 , no goodwill was impaired. Other intangible assets: Other intangible assets consist of core deposit intangible assets and non-compete intangible assets. These items are recorded at fair value when initially recorded. Subsequently, core deposit intangible assets and non-compete intangible assets are amortized primarily on an accelerated basis over periods ranging from ten to fifteen years for core deposit intangible assets and 1 year for non-compete intangible assets and are subject to impairment testing whenever events or changes in circumstances indicate that the carrying amount exceeds the fair value of the asset. If core deposit intangible asset or non-compete intangible asset impairment is identified, the Corporation classifies impaired core deposit intangible assets and impaired non-compete intangible assets subject to nonrecurring fair value measurements as Level 3 valuations. At December 31, 2017 and 2016 , there was no impairment identified for core deposit intangible assets or non-compete intangible assets. Loan servicing rights: Prior to January 1, 2017, LSRs originated by the Corporation and those acquired in acquisitions of other institutions prior to the merger with Talmer were accounted for under the amortization method. The fair value of these LSRs were initially estimated using a model that calculates the net present value of estimated future cash flows using various assumptions, including prepayment speeds, the discount rate and servicing costs. If the valuation model reflects a value less than the carrying value, LSRs are adjusted to fair value, as determined by the model, through a valuation allowance. The Corporation classifies the LSRs subject to nonrecurring fair value measurements as Level 3 valuations. At December 31, 2016 , the Corporation recognized a valuation allowance of $8 thousand related to impairment within certain pools attributable to the Corporation's servicing portfolios. As a result, the LSRs related to these servicing portfolios were considered to be recorded at fair value on a nonrecurring basis as of December 31, 2016 . Other real estate owned and repossessed assets : The carrying amounts for other real estate and repossessed assets are reported in the Consolidated Statements of Financial Position under "Interest receivable and other assets." Other real estate and repossessed assets include real estate and other types of assets repossessed by the Corporation. Other real estate and repossessed assets are recorded at the lower of cost or fair value upon the transfer of a loan to other real estate and repossessed assets and, subsequently, continue to be measured and carried at the lower of cost or fair value. Fair value is based upon independent market prices, appraised values of the property or management's estimation of the value of the property. The Corporation records other real estate and repossessed assets as Level 3 valuations as management generally determines that the fair value of the property is impaired below the appraised value. When management determines the fair value of the property is further impaired below appraised value, discounts ranging between 20% and 30% of the appraised value are used depending on the nature of the property and the age of the most recent appraisal. Disclosure of Nonrecurring Basis Fair Value Measurements For assets measured at fair value on a nonrecurring basis, quantitative disclosures about fair value measurements for each major category of assets follow: (Dollars in thousands) Significant Unobservable Inputs (Level 3) Total December 31, 2017 Impaired loans $ 70,619 $ 70,619 Other real estate and repossessed assets 2,899 2,899 Total $ 73,518 $ 73,518 December 31, 2016 Impaired loans $ 62,184 $ 62,184 Other real estate and repossessed assets 1,386 1,386 Loan servicing rights 2 2 Total $ 63,572 $ 63,572 There were no liabilities recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 . The following table presents additional information about the significant unobservable inputs used in the fair value measurement of financial assets measured on a nonrecurring basis that were categorized within the Level 3 of the fair value hierarchy: (Dollars in thousands) Fair Value at December 31, 2017 Valuation Technique Significant Unobservable Inputs Range Impaired loans $ 70,619 Appraisal of collateral Discount for type of collateral and age of appraisal 20%-30% Other real estate and repossessed assets 2,899 Appraisal of property Discount for type of property and age of appraisal 20%-30% Disclosures About Fair Value of Financial Instruments GAAP requires disclosures about the estimated fair value of the Corporation's financial instruments, including those financial assets and liabilities that are not measured and reported at fair value on a recurring or nonrecurring basis. However, the method of estimating fair value for certain financial instruments, such as loans, that are not required to be measured on a recurring or nonrecurring basis, as prescribed by FASB ASC Topic 820, " Fair Value Measurement ", does not incorporate the exit-price concept of fair value. The Corporation utilized the fair value hierarchy in computing the fair values of its financial instruments. In cases where quoted market prices were not available, the Corporation employed present value methods using unobservable inputs requiring management's judgment to estimate the fair values of its financial instruments, which are considered Level 3 valuations. These Level 3 valuations are affected by the assumptions made and, accordingly, do not necessarily indicate amounts that could be realized in a current market exchange. It is also the Corporation's general practice and intent to hold the majority of its financial instruments until maturity and, therefore, the Corporation does not expect to realize the estimated amounts disclosed. The methodologies for estimating the fair value of financial assets and financial liabilities on a recurring or nonrecurring basis are discussed above. At December 31, 2017 and 2016 , the estimated fair values of cash and cash equivalents, interest receivable and interest payable approximated their carrying values at those dates. The methodologies for other financial assets and financial liabilities follow. Investment securities — held-to-maturity: Fair value measurement for investment securities — held-to-maturity fair values are measured using independent pricing models or other model-based valuation techniques that include market inputs such as benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data and industry and economic events. Fair value measurements using Level 2 valuations of investment securities — held-to-maturity include investment securities issued by state and political subdivisions. Level 3 valuations include trust preferred investment securities. Nonmarketable equity securities: Fair value measurements of nonmarketable equity securities, which consist of Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock, are based on their redeemable value, which is cost. The market for these securities is restricted to the issuer of the stock and subject to impairment evaluation. It is not practicable to determine the fair value of these securities within the fair value hierarchy due to the restrictions placed on their transferability. Loans: The fair values of loans that are not considered impaired are estimated using a discounted cash flow model. The cash flows take into consideration current portfolio interest rates and repricing characteristics as well as assumptions relating to prepayment speeds. The discount rates take into consideration the current market interest rate environment, a credit risk component based on the credit characteristics of each loan portfolio, and a liquidity premium reflecting the liquidity or illiquidity of the market. The fair value measurements for loans are Level 3 valuations. Bank-owned life insurance: Life insurance policies are held on certain officers. The carrying value of these policies approximate fair value as it is based on the cash surrender value adjusted for other charges or amounts due that are probable at settlement. As such, the Corporation classifies the estimated fair value of bank-owned life insurance as Level 2. Bank-owned life insurance is recorded within "Interest receivable and other assets." Deposits: The fair values of deposit accounts without defined maturities, such as interest-and noninterest-bearing checking, savings and money market accounts, are estimated to be the amounts payable on demand. The fair values for variable-interest rate time deposits with defined maturities approximate their carrying amounts. Fair value measurements for fixed-interest rate time deposits with defined maturities are based on the discounted value of contractual cash flows, using the Corporation's interest rates currently being offered for deposits of similar maturities, and are therefore classified as Level 2 valuations. However, if the estimated fair value is less than the carrying value, the carrying value is reported as the fair value. Securities sold under agreements to repurchase: Fair value measurements are based on the present value of future estimated cash flows using current interest rates offered to the Corporation under similar terms and are Level 2 valuations. Short-term borrowings: Short-term borrowings consist of short-term FHLB advances. Fair value measurements for short-term borrowings are based on the present value of future estimated cash flows using current interest rates offered to the Corporation for debt with similar terms and are Level 2 valuations. Lon g -term borrowings: Long-term borrowings consist of long-term FHLB advances, securities sold under agreements to repurchase with an unaffiliated financial institution, a term line-of-credit and subordinated debt obligations. Fair value measurements for long-term borrowings are based on the present value of future estimated cash flows using current interest rates offered to the Corporation for debt with similar terms and are therefore classified as Level 2 valuations. Financial guarantees: The Corporation's unused commitments to extend credit, standby letters of credit and loan commitments have no carrying amount and have been estimated to have no realizable fair value. Historically, a majority of the unused commitments to extend credit have not been drawn upon and, generally, the Corporation does not receive fees in connection with these commitments other than standby letter of credit fees, which are not significant. A summary of carrying amounts and estimated fair values of the Corporation's financial instruments not recorded at fair value in their entirety on a recurring basis on the Consolidated Statements of Financial Position was as follows: December 31, Level in Fair Value Measurement Hierarchy 2017 2016 (Dollars in thousands) Carrying Amount Fair Value Carrying Amount Fair Value Financial assets: Cash and cash equivalents Level 1 $ 455,991 $ 455,991 $ 474,402 $ 474,402 Investment securities: Held-to-maturity Level 2 676,593 662,516 622,927 608,221 Held-to-maturity Level 3 500 390 500 310 Nonmarketable equity securities Level 2 180,091 180,091 97,350 97,350 Net loans (1) Level 3 14,063,380 14,114,545 12,912,511 13,069,315 Interest receivable Level 2 50,710 50,710 42,235 42,235 Bank-owned life insurance Level 2 147,584 147,584 143,718 143,718 Financial liabilities: Deposits: Deposits without defined maturities Level 2 $ 10,425,596 $ 10,425,596 $ 9,862,755 $ 9,862,755 Time deposits Level 2 3,217,207 3,225,847 3,010,367 3,010,048 Total deposits 13,642,803 13,651,443 12,873,122 12,872,803 Interest payable Level 2 6,329 6,329 5,415 5,415 Securities sold under agreements to repurchase with customers Level 2 415,236 415,236 343,047 343,047 Short-term borrowings Level 2 2,000,000 1,999,137 825,000 825,000 Long-term borrowings Level 2 372,882 367,984 597,847 591,227 (1) Included $70.6 million and $62.2 million of impaired loans recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 , respectively.

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities The following is a summary of the amortized cost and fair value of investment securities available-for-sale and investment securities held-to-maturity at December 31, 2017 and 2016 : Investment Securities Available-for-Sale (Dollars in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2017 Government sponsored agencies $ 203,099 $ 765 $ 948 $ 202,916 State and political subdivisions 350,088 310 4,428 345,970 Residential mortgage-backed securities 151,752 5 1,626 150,131 Collateralized mortgage obligations 1,042,240 89 8,484 1,033,845 Corporate bonds 193,230 1,156 1,592 192,794 Preferred stock and trust preferred securities 36,237 1,715 62 37,890 Total $ 1,976,646 $ 4,040 $ 17,140 $ 1,963,546 December 31, 2016 U.S. Treasury securities $ 5,788 $ 5 $ — $ 5,793 Government sponsored agencies 216,890 189 2,068 215,011 State and political subdivisions 311,704 163 11,779 300,088 Residential mortgage-backed securities 276,162 112 3,992 272,282 Collateralized mortgage obligations 323,965 63 4,003 320,025 Corporate bonds 90,859 16 1,401 89,474 Preferred stock and trust preferred securities 31,353 1,018 80 32,291 Total $ 1,256,721 $ 1,566 $ 23,323 $ 1,234,964 Investment Securities Held-to-Maturity (Dollars in thousands) Amortized Cost Unrecognized Gains Unrecognized Losses Fair Value December 31, 2017 State and political subdivisions $ 676,593 $ 3,856 $ 17,933 $ 662,516 Trust preferred securities 500 — 110 390 Total $ 677,093 $ 3,856 $ 18,043 $ 662,906 December 31, 2016 State and political subdivisions $ 622,927 $ 2,648 $ 17,354 $ 608,221 Trust preferred securities 500 — 190 310 Total $ 623,427 $ 2,648 $ 17,544 $ 608,531 The majority of the Corporation's residential mortgage-backed securities and collateralized mortgage obligations are backed by a U.S. government agency (Government National Mortgage Association) or a government sponsored enterprise (Federal Home Loan Mortgage Corporation or Federal National Mortgage Association). Proceeds from sales of securities and the associated gains and losses recorded in earnings are listed below: For the years ended December 31, (Dollars in thousands) 2017 2016 2015 Proceeds $ 409,220 $ 41,446 $ 40,301 Gross gains 178 325 631 Gross losses (7,566 ) (196 ) (1 ) The following is a summary of the amortized cost and fair value of investment securities at December 31, 2017 , by maturity, for both available-for-sale and held-to-maturity investment securities. The maturities of residential mortgage-backed securities and collateralized mortgage obligations are based on scheduled principal payments. The maturities of all other debt securities are based on final contractual maturity. December 31, 2017 (Dollars in thousands) Amortized Cost Fair Value Investment Securities Available-for-Sale: Due in one year or less $ 300,364 $ 298,644 Due after one year through five years 751,998 746,082 Due after five years through ten years 616,027 611,822 Due after ten years 306,868 305,174 Preferred stock 1,389 1,824 Total $ 1,976,646 $ 1,963,546 Investment Securities Held-to-Maturity: Due in one year or less $ 89,359 $ 89,149 Due after one year through five years 237,113 233,022 Due after five years through ten years 152,299 148,185 Due after ten years 198,322 192,550 Total $ 677,093 $ 662,906 Securities with a carrying value of $937.2 million and $794.0 million were pledged at December 31, 2017 and 2016 , respectively, to secure borrowings and deposits. At December 31, 2017 and 2016 , there were no holdings of securities of any one issuer, other than U.S. government and its agencies, in an amount greater than 10% of shareholders' equity. The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at December 31, 2017 and 2016 , aggregated by category and length of time that individual securities have been in a continuous unrealized loss position. As of December 31, 2017 , the Corporation's securities portfolio consisted of 2,329 securities, 1,518 of which were in an unrealized loss position. Less Than 12 Months 12 Months or More Total (Dollars in thousands) Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses December 31, 2017 Government sponsored agencies $ 63,818 $ 510 $ 24,621 $ 438 $ 88,439 $ 948 State and political subdivisions 437,407 12,268 349,242 10,093 786,649 22,361 Residential mortgage-backed securities 93,508 383 56,576 1,243 150,084 1,626 Collateralized mortgage obligations 713,525 7,235 73,707 1,249 787,232 8,484 Corporate bonds 71,447 1,138 47,878 454 119,325 1,592 Preferred stock and trust preferred securities — — 11,164 172 11,164 172 Total $ 1,379,705 $ 21,534 $ 563,188 $ 13,649 $ 1,942,893 $ 35,183 December 31, 2016 Government sponsored agencies $ 105,702 $ 1,707 $ 15,023 $ 361 $ 120,725 $ 2,068 State and political subdivisions 758,063 28,158 26,810 975 784,873 29,133 Residential mortgage-backed securities 244,239 3,992 — — 244,239 3,992 Collateralized mortgage obligations 279,001 3,778 14,754 225 293,755 4,003 Corporate bonds 80,536 1,401 — — 80,536 1,401 Preferred stock and trust preferred securities 10,699 80 310 190 11,009 270 Total $ 1,478,240 $ 39,116 $ 56,897 $ 1,751 $ 1,535,137 $ 40,867 An assessment is performed quarterly by the Corporation to determine whether unrealized losses in its investment securities portfolio are temporary or other-than-temporary by carefully considering all reasonably available information. The Corporation reviews factors such as financial statements, credit ratings, news releases and other pertinent information of the underlying issuer or company to make its determination. Management did not believe any individual unrealized loss on any investment security at December 31, 2017 , represented an other-than-temporary impairment (OTTI) as the unrealized losses for these securities resulted primarily from changes in benchmark U.S. Treasury interest rates and not credit issues. Management believed that the unrealized losses on investment securities at December 31, 2017 were temporary in nature and due primarily to changes in interest rates and reduced market liquidity and not as a result of credit-related issues. At December 31, 2017 , the Corporation did not have the intent to sell any of its impaired investment securities and believed that it was more-likely-than-not that the Corporation will not have to sell any such investment securities before a full recovery of amortized cost. Accordingly, at December 31, 2017 , the Corporation believed the impairments in its investment securities portfolio were temporary in nature. However, there is no assurance that OTTI may not occur in the future.

Loans

Loans	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loans	Loans Loan portfolio segments are defined as the level at which an entity develops and documents a systematic methodology to determine its allowance. The Corporation has two loan portfolio segments (commercial loans and consumer loans) that it uses in determining the allowance. Both quantitative and qualitative factors are used by management at the loan portfolio segment level in determining the adequacy of the allowance for the Corporation. Classes of loans are a disaggregation of an entity's loan portfolio segments. Classes of loans are defined as a group of loans which share similar initial measurement attributes, risk characteristics and methods for monitoring and assessing credit risk. The Corporation has six classes of loans, which are set forth below. Commercial — Loans and lines of credit to varying types of businesses, including municipalities, school districts and nonprofit organizations, for the purpose of supporting working capital, operational needs and term financing of equipment. Repayment of such loans is generally provided through operating cash flows of the business. Commercial loans are predominately secured by equipment, inventory, accounts receivable, personal guarantees of the owner and other sources of repayment, although the Corporation may also secure commercial loans with real estate. Commercial real estate — Loans secured by real estate occupied by the borrower for ongoing operations, non-owner occupied real estate leased to one or more tenants and vacant land that has been acquired for investment or future land development. Real estate construction and land development — Real estate construction loans represent secured loans for the construction of business properties. Real estate construction loans often convert to a commercial real estate loan at the completion of the construction period. Land development loans represent secured development loans made to borrowers for the purpose of infrastructure improvements to vacant land to create finished marketable residential and commercial lots/land. Most land development loans are originated with the intention that the loans will be paid through the sale of developed lots/land by the developers within twelve months of the completion date. Land development loans at December 31, 2017 and 2016 were primarily comprised of loans to develop residential properties. Residential mortgage — Loans secured by one - to four -family residential properties, generally with fixed interest rates for periods of fifteen years or less. The loan-to-value ratio at the time of origination is generally 80% or less. Residential mortgage loans with a loan-to-value ratio of more than 80% generally require private mortgage insurance. Consumer installment — Loans to consumers primarily for the purpose of acquiring automobiles, recreational vehicles and personal watercraft and comprised primarily of indirect loans purchased from dealers. These loans consist of relatively small amounts that are spread across many individual borrowers. Home equity — Loans and lines of credit whereby consumers utilize equity in their personal residence, generally through a second mortgage, as collateral to secure the loan. Commercial, commercial real estate, real estate construction and land development loans are referred to as the Corporation's commercial loan portfolio, while residential mortgage, consumer installment and home equity loans are referred to as the Corporation's consumer loan portfolio. A summary of the Corporation's loans follows: (Dollars in thousands) Originated Acquired (1) Total loans December 31, 2017 Commercial loan portfolio: Commercial $ 2,407,606 $ 978,036 $ 3,385,642 Commercial real estate 2,751,425 1,749,245 4,500,670 Real estate construction and land development 498,155 76,060 574,215 Subtotal 5,657,186 2,803,341 8,460,527 Consumer loan portfolio: Residential mortgage 1,967,857 1,284,630 3,252,487 Consumer installment 1,510,540 102,468 1,613,008 Home equity 611,846 217,399 829,245 Subtotal 4,090,243 1,604,497 5,694,740 Total loans (2) $ 9,747,429 $ 4,407,838 $ 14,155,267 December 31, 2016 Commercial loan portfolio: Commercial $ 1,901,526 $ 1,315,774 $ 3,217,300 Commercial real estate 1,921,799 2,051,341 3,973,140 Real estate construction and land development 281,724 122,048 403,772 Subtotal 4,105,049 3,489,163 7,594,212 Consumer loan portfolio: Residential mortgage 1,475,342 1,611,132 3,086,474 Consumer installment 1,282,588 151,296 1,433,884 Home equity 595,422 280,787 876,209 Subtotal 3,353,352 2,043,215 5,396,567 Total loans (2) $ 7,458,401 $ 5,532,378 $ 12,990,779 (1) Acquired loans are accounted for under ASC 310-30. (2) Reported net of deferred costs totaling $26.1 million and $14.8 million at December 31, 2017 and 2016 , respectively. The Corporation acquired loans at fair value as of the acquisition date, which includes loans acquired in the acquisitions of Talmer, Lake Michigan Financial Corporation ("Lake Michigan"), Monarch Community Bancorp, Inc. ("Monarch"), Northwestern Bancorp, Inc. ("Northwestern") and O.A.K. Financial Corporation ("OAK"). Acquired loans are accounted for under ASC 310-30 which recognizes the expected shortfall of expected future cash flows, as compared to the contractual amount due, as nonaccretable discount. Any excess of the net present value of expected future cash flows over the acquisition date fair value is recognized as the accretable discount, or accretable yield. The accretable discount is recognized over the expected remaining life of the acquired loans on a pool basis. In the event an acquired loan is renewed or extended, the loan continues to be accounted for as an acquired loan on a pool basis in accordance with ASC 310-30. Activity for the accretable yield is as follows: (Dollars in thousands) Talmer Lake Michigan Monarch North-western OAK Total Year Ended December 31, 2017 Balance at beginning of period $ 798,210 $ 121,416 $ 27,182 $ 69,847 $ 23,316 $ 1,039,971 Accretion recognized in interest income (175,678 ) (29,077 ) (4,533 ) (20,318 ) (12,563 ) (242,169 ) Net reclassification (to) from nonaccretable difference (1) 108,821 2,785 (153 ) 11,285 6,357 129,095 Balance at end of period $ 731,353 $ 95,124 $ 22,496 $ 60,814 $ 17,110 $ 926,897 Year Ended December 31, 2016 Balance at beginning of period $ — $ 152,999 $ 34,558 $ 82,623 $ 28,077 $ 298,257 Addition attributable to acquisitions 862,127 — — — — 862,127 Additions (reductions) (1) — (3,552 ) (1,908 ) (6,985 ) 1,091 (11,354 ) Accretion recognized in interest income (63,917 ) (33,031 ) (5,468 ) (15,791 ) (13,352 ) (131,559 ) Net reclassification (to) from nonaccretable difference (1) — 5,000 — 10,000 7,500 22,500 Balance at end of period $ 798,210 $ 121,416 $ 27,182 $ 69,847 $ 23,316 $ 1,039,971 Year Ended December 31, 2015 Balance at beginning of period $ — $ — $ — $ 104,675 $ 33,286 $ 137,961 Addition attributable to acquisitions — 190,246 37,914 — — 228,160 Additions (reductions) (1) — (12,991 ) 1,336 (3,396 ) 6,601 (8,450 ) Accretion recognized in interest income — (24,256 ) (4,692 ) (18,656 ) (11,810 ) (59,414 ) Net reclassification (to) from nonaccretable difference (1) — — — — — — Balance at end of period $ — $ 152,999 $ 34,558 $ 82,623 $ 28,077 $ 298,257 (1) The net reclassification results from changes in expected cash flows of the acquired loans which may include increases in the amount of contractual principal and interest expected to be collected due to improvement in credit quality, increases in balances outstanding from advances, renewals, extensions and interest rates; as well as reductions in contractual principal and interest expected to be collected due to credit deterioration, payoffs, and decreases in interest rates. Chemical Bank has extended loans to its directors, executive officers and their affiliates. These loans were made in the ordinary course of business upon normal terms, including collateralization and interest rates prevailing at the time, and did not involve more than the normal risk of repayment by the borrower. The aggregate loans outstanding to the directors, executive officers and their affiliates totaled $3.8 million at December 31, 2017 and $23.9 million at December 31, 2016 . During 2017 and 2016 , there were $44.1 million and $33.8 million , respectively, of new loans and other additions, while repayments and other reductions totaled $64.2 million and $31.6 million , respectively. Loans held-for-sale, comprised of fixed-rate residential mortgage loans, were $52.1 million at December 31, 2017 and $81.8 million at December 31, 2016 . The Corporation sold loans totaling $806.8 million in 2017 , $707.8 million in 2016 and $222.6 million in 2015 . Credit Quality Monitoring The Corporation maintains loan policies and credit underwriting standards as part of the process of managing credit risk. These standards include making loans generally only within the Corporation's market areas. The Corporation's lending markets generally consist of communities throughout Michigan and additional communities located within northwest Ohio and northern Indiana. The Corporation, through Chemical Bank, has a commercial loan portfolio approval process involving underwriting and individual and group loan approval authorities to consider credit quality and loss exposure at loan origination. The loans in the Corporation's commercial loan portfolio are risk rated at origination based on the grading system set forth below. The approval authority of relationship managers is established based on experience levels, with credit decisions greater than $1.25 million requiring credit officer approval and credit decisions greater than $3.0 million requiring group loan authority approval, except for six executive and senior officers who have varying loan limits up to $8.0 million . With respect to the group loan authorities, Chemical Bank has various regional loan committees that meet weekly to consider loan ranging in amounts from $3.0 million to $7.0 million , and a senior loan committee, consisting of certain executive and senior officers, that meets weekly to consider loans ranging in amounts from $5.0 million up to Chemical Bank's internal lending limit, depending on risk rating and credit action required. Credit decisions exceeding Chemical Bank's internal lending limit require the approval of the board of directors. The majority of the Corporation's consumer loan portfolio is comprised of secured loans that are relatively small. The Corporation's consumer loan portfolio has a centralized approval process which utilizes standardized underwriting criteria. The ongoing measurement of credit quality of the consumer loan portfolio is largely done on an exception basis. If payments are made on schedule, as agreed, then no further monitoring is performed. However, if delinquency occurs, the delinquent loans are turned over to the Corporation's collection department for resolution, resulting in repossession or foreclosure if payments are not brought current. Credit quality for the entire consumer loan portfolio is measured by the periodic delinquency rate, nonaccrual amounts and actual losses incurred. Loans in the commercial loan portfolio tend to be larger and more complex than those in the consumer loan portfolio, and therefore, are subject to more intensive monitoring. All loans in the commercial loan portfolio have an assigned relationship manager, and most borrowers provide periodic financial and operating information that allows the relationship managers to stay abreast of credit quality during the life of the loans. The risk ratings of loans in the commercial loan portfolio are reassessed at least annually, with loans below an acceptable risk rating reassessed more frequently and reviewed by various loan committees within the Corporation at least quarterly. The Corporation maintains a centralized independent loan review function that monitors the approval process and ongoing asset quality of the loan portfolio, including the accuracy of loan grades. The Corporation also maintains an independent appraisal review function that participates in the review of all appraisals obtained by the Corporation for loans in the commercial loan portfolio. Credit Quality Indicators Commercial Loan Portfolio Risk categories for the Corporation's commercial loan portfolio establish the credit quality of a borrower by measuring liquidity, debt capacity, coverage and payment behavior as shown in the borrower's financial statements. The risk categories also measure the quality of the borrower's management and the repayment support offered by any guarantors. Risk categories for the Corporation's commercial loan portfolio are described as follows: Pass: Includes all loans without weaknesses or potential weaknesses identified in the categories of special mention, substandard or doubtful. Special Mention: Loans with potential credit weakness or credit deficiency, which, if not corrected, pose an unwarranted financial risk that could weaken the loan by adversely impacting the future repayment ability of the borrower. Substandard: Loans with a well-defined weakness, or weaknesses, such as loans to borrowers who may be experiencing losses from operations or inadequate liquidity of a degree and duration that jeopardizes the orderly repayment of the loan. Substandard loans also are distinguished by the distinct possibility of loss in the future if these weaknesses are not corrected. Doubtful: Loans with all the characteristics of a loan classified as Substandard, with the added characteristic that credit weaknesses make collection in full highly questionable and improbable. The primary source of repayment is nonexistent and there is doubt as to the value of the secondary source of repayments. A doubtful asset has a high probability of total or substantial loss, but because of pending events that may strengthen the asset, its classification as loss is deferred. Loss: An asset classified as loss is considered uncollectible and of such little value that the continuance as a bankable asset is not warranted. This classification does not mean that an asset has absolutely no recovery or salvage value, but rather that it is not practical or desirable to defer writing off this basically worthless asset even through partial recovery may occur in the future. The following schedule presents the recorded investment of loans in the commercial loan portfolio by credit risk categories at December 31, 2017 and 2016 : (Dollars in thousands) Pass Special Mention Substandard Doubtful Total December 31, 2017 Originated Portfolio: Commercial $ 2,316,464 $ 41,059 $ 50,083 $ — $ 2,407,606 Commercial real estate 2,677,579 24,204 49,642 — 2,751,425 Real estate construction and land development 494,528 837 2,790 — 498,155 Subtotal 5,488,571 66,100 102,515 — 5,657,186 Acquired Portfolio: Commercial 873,861 68,418 35,539 218 978,036 Commercial real estate 1,603,685 67,970 76,803 787 1,749,245 Real estate construction and land development 72,346 2,218 1,496 — 76,060 Subtotal 2,549,892 138,606 113,838 1,005 2,803,341 Total $ 8,038,463 $ 204,706 $ 216,353 $ 1,005 $ 8,460,527 December 31, 2016 Originated Portfolio: Commercial $ 1,803,750 $ 44,809 $ 51,898 $ 1,069 $ 1,901,526 Commercial real estate 1,849,315 36,981 35,502 1 1,921,799 Real estate construction and land development 280,968 157 599 — 281,724 Subtotal 3,934,033 81,947 87,999 1,070 4,105,049 Acquired Portfolio: Commercial 1,218,848 46,643 50,283 — 1,315,774 Commercial real estate 1,897,011 61,441 92,636 253 2,051,341 Real estate construction and land development 117,505 1,982 2,561 — 122,048 Subtotal 3,233,364 110,066 145,480 253 3,489,163 Total $ 7,167,397 $ 192,013 $ 233,479 $ 1,323 $ 7,594,212 Consumer Loan Portfolio The Corporation evaluates the credit quality of loans in the consumer loan portfolio based on the performing or nonperforming status of the loan. Loans in the consumer loan portfolio that are performing in accordance with original contractual terms and are less than 90 days past due and accruing interest are considered to be in a performing status, while those that are in nonaccrual status, contractually past due 90 days or more as to interest or principal payments are considered to be in a nonperforming status. Loans accounted for under ASC 310-30, "Acquired loans", that are not performing in accordance with contractual terms are not reported as nonperforming because these loans are recorded in pools at their net realizable value based on the principal and interest the Corporation expects to collect on these loans. The following schedule presents the recorded investment of loans in the consumer loan portfolio based on loans in a performing status and loans in a nonperforming status at December 31, 2017 and 2016 : (Dollars in thousands) Residential mortgage Consumer installment Home equity Total consumer December 31, 2017 Originated Portfolio: Performing $ 1,959,222 $ 1,509,698 $ 607,541 $ 4,076,461 Nonperforming 8,635 842 4,305 13,782 Subtotal 1,967,857 1,510,540 611,846 4,090,243 Acquired Loans 1,284,630 102,468 217,399 1,604,497 Total $ 3,252,487 $ 1,613,008 $ 829,245 $ 5,694,740 December 31, 2016 Originated Portfolio: Performing $ 1,468,373 $ 1,281,709 $ 592,071 $ 3,342,153 Nonperforming 6,969 879 3,351 11,199 Subtotal 1,475,342 1,282,588 595,422 3,353,352 Acquired Loans 1,611,132 151,296 280,787 2,043,215 Total $ 3,086,474 $ 1,433,884 $ 876,209 $ 5,396,567 Nonperforming Assets and Past Due Loans Nonperforming assets consist of loans for which the accrual of interest has been discontinued, other real estate owned acquired through acquisitions, other real estate owned obtained through foreclosure and other repossessed assets. Loans are considered past due or delinquent when the contractual principal or interest due in accordance with the terms of the loan agreement or any portion thereof remains unpaid after the due date of the scheduled payments. Loans outside of those accounted for under ASC 310-30 are classified as nonaccrual when, in the opinion of management, collection of principal or interest is doubtful. The accrual of interest is discontinued when a loan is placed in nonaccrual status and any payments received reduce the carrying value of the loan. A loan may be placed back on accrual status if all contractual payments have been received and collection of future principal and interest payments are no longer doubtful. Acquired loans that are not performing in accordance with contractual terms are not reported as nonperforming because these loans are recorded in pools at their net realizable value based on the principal and interest the Corporation expects to collect on these loans. A summary of nonperforming assets follows: December 31, (Dollars in thousands) 2017 2016 Nonperforming assets Nonaccrual loans: Commercial $ 19,691 $ 13,178 Commercial real estate 29,545 19,877 Real estate construction and land development 77 80 Residential mortgage 8,635 6,969 Consumer installment 842 879 Home equity 4,305 3,351 Total nonaccrual loans 63,095 44,334 Other real estate owned and repossessed assets 8,807 17,187 Total nonperforming assets $ 71,902 $ 61,521 Accruing loans contractually past due 90 days or more as to interest or principal payments, excluding acquired loans accounted for under ASC 310-30 Commercial $ — $ 11 Commercial real estate 13 277 Residential mortgage — — Home equity 1,364 995 Total accruing loans contractually past due 90 days or more as to interest or principal payments, excluding acquired loans accounted for under ASC 310-30 $ 1,377 $ 1,283 The Corporation's nonaccrual loans at December 31, 2017 and 2016 included $29.1 million and $30.5 million , respectively, of nonaccrual TDRs. There was no interest income recognized on nonaccrual loans during 2017 , 2016 and 2015 while the loans were in nonaccrual status. During 2017 , 2016 and 2015 , the Corporation recognized $1.3 million , $0.4 million and $0.9 million , respectively, of interest income on these loans while they were in an accruing status. Additional interest income that would have been recorded on nonaccrual loans had they been current in accordance with their original terms was $3.1 million in 2017 , $2.9 million in 2016 and $3.2 million in 2015 . During 2017 , 2016 and 2015 , the Corporation recognized interest income of $2.6 million , $3.9 million and $3.9 million , respectively, on performing TDRs. The Corporation had $4.2 million of residential mortgage loans that were in the process of foreclosure at December 31, 2017 , compared to $7.3 million at December 31, 2016 . Loan delinquency, excluding acquired loans accounted for under ASC 310-30, was as follows: (Dollars in thousands) 30-59 days past due 60-89 days past due 90 days or more past due Total past due Current Total loans 90 days or more past due and still accruing December 31, 2017 Originated Portfolio: Commercial $ 13,906 $ 3,766 $ 9,494 $ 27,166 $ 2,380,440 $ 2,407,606 $ — Commercial real estate 9,380 1,562 5,873 16,815 2,734,610 2,751,425 13 Real estate construction and land development — — — — 498,155 498,155 — Residential mortgage 2,795 1,415 858 5,068 1,962,789 1,967,857 — Consumer installment 3,324 442 226 3,992 1,506,548 1,510,540 — Home equity 2,319 1,301 2,196 5,816 606,030 611,846 1,364 Total $ 31,724 $ 8,486 $ 18,647 $ 58,857 $ 9,688,572 $ 9,747,429 $ 1,377 December 31, 2016 Originated Portfolio: Commercial $ 10,421 $ 4,842 $ 3,641 $ 18,904 $ 1,882,622 $ 1,901,526 $ 11 Commercial real estate 6,551 1,589 5,165 13,305 1,908,494 1,921,799 277 Real estate construction and land development 2,721 499 — 3,220 278,504 281,724 — Residential mortgage 3,147 62 1,752 4,961 1,470,381 1,475,342 — Consumer installment 3,991 675 238 4,904 1,277,684 1,282,588 — Home equity 3,097 893 2,349 6,339 589,083 595,422 995 Total $ 29,928 $ 8,560 $ 13,145 $ 51,633 $ 7,406,768 $ 7,458,401 $ 1,283 Impaired Loans A loan is impaired when, based on current information and events, it is probable that the Corporation will be unable to collect all amounts due according to the contractual terms of the loan agreement. Impaired loans include nonperforming loans and all TDRs. Impaired loans are accounted for at the lower of the present value of expected cash flows or the estimated fair value of the collateral. When the present value of expected cash flows or the fair value of the collateral of an impaired loan not accounted for under ASC 310-30 is less than the amount of unpaid principal outstanding on the loan, the recorded principal balance of the loan is reduced to its carrying value through either a specific allowance for loan loss or a partial charge-off of the loan balance. The following schedules present impaired loans by classes of loans at December 31, 2017 and December 31, 2016 : (Dollars in thousands) Recorded investment Unpaid principal balance Related valuation allowance December 31, 2017 Impaired loans with a valuation allowance: Commercial $ 28,897 $ 31,655 $ 2,296 Commercial real estate 28,003 34,580 3,227 Real estate construction and land development 313 313 14 Residential mortgage 15,872 15,872 1,487 Consumer installment 966 966 120 Home equity 4,570 4,570 858 Subtotal 78,621 87,956 8,002 Impaired loans with no related valuation allowance: Commercial 8,504 9,291 — Commercial real estate 18,080 19,861 — Real estate construction and land development — — — Residential mortgage 4,902 4,902 — Consumer installment — — — Home equity 1,770 1,770 — Subtotal 33,256 35,824 — Total impaired loans: Commercial 37,401 40,946 2,296 Commercial real estate 46,083 54,441 3,227 Real estate construction and land development 313 313 14 Residential mortgage 20,774 20,774 1,487 Consumer installment 966 966 120 Home equity 6,340 6,340 858 Total $ 111,877 $ 123,780 $ 8,002 (Dollars in thousands) Recorded investment Unpaid principal balance Related valuation allowance December 31, 2016 Impaired loans with a valuation allowance: Commercial $ 28,925 $ 33,209 $ 3,128 Commercial real estate 21,318 27,558 2,102 Real estate construction and land development 177 177 4 Residential mortgage 20,864 20,864 3,528 Consumer installment 879 879 240 Home equity 2,577 2,577 390 Subtotal 74,740 85,264 9,392 Impaired loans with no related valuation allowance: Commercial 7,435 11,153 — Commercial real estate 20,588 23,535 — Real estate construction and land development 80 80 — Residential mortgage 3,252 3,252 — Consumer installment — — — Home equity 774 774 — Subtotal 32,129 38,794 — Total impaired loans: Commercial 36,360 44,362 3,128 Commercial real estate 41,906 51,093 2,102 Real estate construction and land development 257 257 4 Residential mortgage 24,116 24,116 3,528 Consumer installment 879 879 240 Home equity 3,351 3,351 390 Total $ 106,869 $ 124,058 $ 9,392 The following schedule presents additional information regarding impaired loans by classes of loans segregated by those requiring a valuation allowance and those not requiring a valuation allowance at December 31, 2017 , 2016 and 2015 and the respective interest income amounts recognized: For the years ended December 31, 2017 2016 2015 (Dollars in thousands) Average annual recorded investment Interest income recognized while on impaired status Average annual recorded investment Interest income recognized while on impaired status Average annual recorded investment Interest income recognized while on impaired status Impaired loans with a valuation allowance: Commercial $ 25,099 $ 939 $ 7,829 $ — $ 9,511 $ — Commercial real estate 19,983 677 5,658 — 2,918 — Real estate construction and land development 175 10 19 — — — Residential mortgage 16,390 538 23,958 1,285 20,661 1,312 Consumer installment 744 4 359 — — — Home equity 4,201 82 1,759 — — — Subtotal 66,592 2,250 39,582 1,285 33,090 1,312 Impaired loans with no related valuation allowance: Commercial 10,196 28 29,559 1,343 27,778 1,005 Commercial real estate 24,658 245 41,646 1,236 50,079 1,547 Real estate construction and land development 78 — 585 22 889 25 Residential mortgage 4,622 38 1,519 — 6,027 — Consumer installment 205 — — — 448 — Home equity 1,392 14 555 — 1,872 — Subtotal 41,151 325 73,864 2,601 87,093 2,577 Total impaired loans: Commercial 35,295 967 37,388 1,343 37,289 1,005 Commercial real estate 44,641 922 47,304 1,236 52,997 1,547 Real estate construction and land development 253 10 604 22 889 25 Residential mortgage 21,012 576 25,477 1,285 26,688 1,312 Consumer installment 949 4 359 — 448 — Home equity 5,593 96 2,314 — 1,872 — Total $ 107,743 $ 2,575 $ 113,446 $ 3,886 $ 120,183 $ 3,889 The difference between an impaired loan's recorded investment and the unpaid principal balance for originated loans represents a partial charge-off resulting from a confirmed loss due to the value of the collateral securing the loan being below the loan balance and management's assessment that full collection of the loan balance is not likely. Impaired loans included $48.8 million and $62.5 million at December 31, 2017 and December 31, 2016 , respectively, of accruing TDRs. Loans Modified Under Troubled Debt Restructurings (TDRs) The following tables present the recorded investment of loans modified into TDRs during the years ended December 31, 2017 , 2016 and 2015 by type of concession granted. In cases where more than one type of concession was granted, the loans were categorized based on the most significant concession. Concession type (Dollars in thousands) Principal Principal A/B Note Restructure (1) Interest Forbearance Total Pre- modification recorded investment Post- modification recorded investment For the year ended December 31, 2017 Commercial loan portfolio: Commercial $ 2,308 $ — $ — $ 1,827 $ 2,176 36 $ 6,416 $ 6,311 Commercial real estate 706 — — 338 953 16 2,097 1,997 Real estate construction and land development 35 — — — — 1 36 35 Subtotal 3,049 — — 2,165 3,129 53 8,549 8,343 Consumer loan portfolio: Residential mortgage 297 — — 383 — 11 763 680 Consumer installment 118 37 — 37 — 34 208 192 Home equity 389 — — 52 — 14 537 441 Subtotal 804 37 — 472 — 59 1,508 1,313 Total loans $ 3,853 $ 37 $ — $ 2,637 $ 3,129 112 $ 10,057 $ 9,656 For the year ended December 31, 2016 Commercial loan portfolio: Commercial $ 11,533 $ 1,527 $ 43 $ — $ 1,750 54 $ 14,853 $ 14,853 Commercial real estate 2,993 1,866 — — — 16 4,859 4,859 Subtotal 14,526 3,393 43 — 1,750 70 19,712 19,712 Consumer loan portfolio: Residential mortgage 477 — — — — 4 477 477 Consumer installment 87 — — — — 14 87 87 Home equity 179 — — 364 — 10 543 543 Subtotal 743 — — 364 — 28 1,107 1,107 Total loans $ 15,269 $ 3,393 $ 43 $ 364 $ 1,750 98 $ 20,819 $ 20,819 For the year ended December 31, 2015 Commercial loan portfolio: Commercial $ 6,031 $ — $ — $ 117 $ 5,298 53 $ 11,446 $ 11,446 Commercial real estate 5,904 450 — 102 740 21 7,196 7,196 Real estate construction and land development 705 — — — — 3 705 705 Subtotal 12,640 450 — 219 6,038 77 19,347 19,347 Consumer loan portfolio: Residential mortgage 1,246 — — 635 — 20 1,881 1,881 Consumer installment 210 — — — — 19 210 210 Home equity 1,110 — — 46 — 26 1,158 1,156 Subtotal 2,566 — — 681 — 65 3,249 3,247 Total loans $ 15,206 $ 450 $ — $ 900 $ 6,038 142 $ 22,596 $ 22,594 (1) Loan restructurings whereby the original loan is restructured into two notes: an "A" note, which generally reflects the portion of the modified loans which is expected to be collected: and a "B" note, which is fully charged off. The pre-modification and post-modification recorded investment represents amounts as of the date of loan modification. The difference between the pre-modification and post-modification recorded investment of residential mortgage TDRs represents impairment recognized by the Corporation through the provision for loan losses computed based on a loan's post-modification present value of expected future cash flows discounted at the loan's original effective interest rate. The following schedule presents the Corporation's TDRs at December 31, 2017 and 2016 : (Dollars in thousands) Accruing TDRs Nonaccrual TDRs Total December 31, 2017 Commercial loan portfolio $ 34,484 $ 24,358 $ 58,842 Consumer loan portfolio 14,298 4,748 19,046 Total $ 48,782 $ 29,106 $ 77,888 December 31, 2016 Commercial loan portfolio $ 45,388 $ 25,397 $ 70,785 Consumer loan portfolio 17,147 5,134 22,281 Total $ 62,535 $ 30,531 $ 93,066 The following schedule includes TDRs for which there was a payment default during the years ended December 31, 2017 , 2016 and 2015 , whereby the borrower was past due with respect to principal and/or interest for 90 days or more, and the loan became a TDR during the twelve-month period prior to the default: For the years ended December 31, 2017 2016 2015 Number of loans Principal balance at year end Number of loans Principal balance at year end Number of loans Principal balance at year end (Dollars in thousands) Commercial loan portfolio: Commercial 5 $ 1,617 — $ — 1 $ 1,206 Commercial real estate — — 2 1,721 5 1,016 Subtotal - commercial loan portfolio 5 1,617 2 1,721 6 2,222 Consumer loan portfolio (residential mortgage) 17 434 14 259 3 65 Total 22 $ 2,051 16 $ 1,980 9 $ 2,287 At December 31, 2017 , commitments to lend additional funds to borrowers whose terms have been modified in TDRs totaled $2.0 million . Allowance for Loan Losses The following schedule presents, by loan portfolio segment, the changes in the allowance for the originated loan portfolio for the years ended December 31, 2017 , 2016 and 2015 . (Dollars in thousands) Commercial loan portfolio Consumer loan portfolio Unallocated Total Originated Loan Portfolio Changes in allowance for loan losses for the year ended December 31, 2017: Beginning balance $ 51,201 $ 27,067 $ — $ 78,268 Provision for loan losses 19,007 4,293 — 23,300 Charge-offs (8,570 ) (8,297 ) — (16,867 ) Recoveries 4,495 2,691 — 7,186 Ending balance $ 66,133 $ 25,754 $ — $ 91,887 Changes in allowance for loan losses for the year ended December 31, 2016: Beginning balance $ 47,234 $ 26,094 $ — $ 73,328 Provision (benefit) for loan losses 9,788 5,087 — 14,875 Charge-offs (8,906 ) (6,396 ) — (15,302 ) Recoveries 3,085 2,282 — 5,367 Ending balance $ 51,201 $ 27,067 $ — $ 78,268 Changes in allowance for loan losses for the year ended December 31, 2015: Beginning balance $ 44,156 $ 28,803 $ 2,724 $ 75,683 Provision (benefit) for loan losses 7,275 1,949 (2,724 ) 6,500 Charge-offs (6,385 ) (7,116 ) — (13,501 ) Recoveries 2,188 2,458 — 4,646 Ending balance $ 47,234 $ 26,094 $ — $ 73,328 The following schedule presents by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2017 and 2016 by impairment evaluation method. (Dollars in thousands) Commercial Consumer

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment	Premises and Equipment The following table summarizes premises and equipment: December 31, (Dollars in thousands) 2017 2016 Land and land improvements $ 31,427 $ 36,185 Buildings 130,028 144,155 Furniture and equipment 100,932 91,963 Total 262,387 272,303 Less accumulated depreciation (135,491 ) (127,291 ) Premises and equipment, net $ 126,896 $ 145,012 The Corporation leases certain branch properties and equipment under operating leases. Net rent expense was $6.4 million , $3.3 million and $1.7 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. During the years ended December 31, 2017 and 2016 the Corporation transferred $13.2 million and $4.8 million from premises and equipment to other assets, respectively, due to branch or building operation closings/consolidations.

Other Real Estate Owned and Rep

Other Real Estate Owned and Repossessed Assets	12 Months Ended
	Dec. 31, 2017
Other Real Estate [Abstract]
Other Real Estate Owned and Repossessed Assets	Other Real Estate Owned and Repossessed Assets Changes in other real estate owned and repossessed assets, included in interest receivable and other assets on the Consolidated Statements of Financial Position, were as follows: (Dollars in thousands) Other real estate Repossessed Balance at January 1, 2015 $ 13,953 $ 252 Additions due to acquisitions 440 — Other additions (1) 6,957 2,372 Net payments received (45 ) (22 ) Disposals (10,168 ) (2,383 ) Write-downs (1,421 ) — Balance at December 31, 2015 $ 9,716 $ 219 Additions due to acquisitions 13,227 313 Other additions (1) 9,938 3,032 Net payments received (1,560 ) (763 ) Disposals (13,873 ) (2,426 ) Write-downs (636 ) — Balance at December 31, 2016 $ 16,812 $ 375 Other additions (1) 6,905 4,641 Net payments received (1,064 ) — Disposals (12,831 ) (4,391 ) Write-downs (1,640 ) — Balance at December 31, 2017 $ 8,182 $ 625 (1) Includes loans transferred to other real estate owned and other repossessed assets. At December 31, 2017 the Corporation had $0.5 million of other real estate owned and repossessed assets as a result of obtaining physical possession in accordance with ASU No. 2014-04, Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans Upon Foreclosure. In addition, there were $4.2 million of consumer mortgage loans secured by residential real estate properties for which formal foreclosure proceedings are in process, as of December 31, 2017 . Income and expenses related to other real estate owned and repossessed assets, recorded as a component of “Other expense” in the Consolidated Statements of Income, were as follows: (Dollars in thousands) Other real estate owned Repossessed assets For the year ended December 31, 2017 Net gain (loss) on sale $ 3,038 $ (381 ) Write-downs (1,640 ) — Net operating expenses (1,981 ) (41 ) Total $ (583 ) $ (422 ) For the year ended December 31, 2016 Net gain (loss) on sale $ 5,325 $ 523 Write-downs (636 ) — Net operating expenses (740 ) (60 ) Total $ 3,949 $ 463 For the year ended December 31, 2015 Net gain (loss) on sale $ 4,128 $ (26 ) Write-downs (1,421 ) — Net operating expenses (1,604 ) (19 ) Total $ 1,103 $ (45 )

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill Goodwill was $1.13 billion for both December 31, 2017 and 2016 . Goodwill recorded is primarily attributable to the synergies and economies of scale expected from combining the operations of the Corporation and acquired and merged organizations. The Corporation recorded goodwill in the amount of $847.7 million related to the merger with Talmer completed on August 31, 2016. During 2015, the Corporation acquired Lake Michigan and Monarch, which resulted in the recognition of goodwill for each transaction of $101.1 million and $5.3 million , respectively. Goodwill is not amortized but is subject to impairment testing annually as of October 31 and on an interim basis if events or changes in circumstances indicate assets might be impaired. Impairment exists when the carrying value of goodwill exceeds its fair value. The Corporation’s most recent annual goodwill impairment review performed as of October 31, 2017 did not indicate that an impairment of goodwill existed. The Corporation also determined that no triggering events have occurred that indicated impairment from the most recent valuation date through December 31, 2017 and that the Corporation's goodwill was no t impaired at December 31, 2017 .

Loan Servicing Rights

Loan Servicing Rights	12 Months Ended
	Dec. 31, 2017
Transfers and Servicing [Abstract]
Loan Servicing Rights	Loan Servicing Rights LSRs are created as a result of selling residential mortgage and commercial real estate loans in the secondary market while retaining the right to service these loans and receive servicing income over the life of the loan, and from acquisitions of other banks that had LSRs. Loans serviced for others are not reported as assets in the Consolidated Statements of Financial Position. The Corporation elected to account for LSRs acquired related to the merger with Talmer under the fair value measurement method. Prior to January 1, 2017, the Corporation accounted for all other LSRs at the lower of cost or fair value ("Amortized LSRs"). The Corporation elected as of January 1, 2017 to account for all previously Amortized LSRs under the fair value measurement method. This change in accounting policy resulted in a cumulative adjustment to retained earnings as of January 1, 2017 in the amount of $3.7 million . For further information on this election, refer to Note 1, Basis of Presentation and Significant Accounting Policies. LSRs are established and recorded at the estimated fair value by calculating the present value of estimated future net servicing cash flows, taking into consideration actual and expected mortgage loan prepayment rates, discount rates, servicing costs, and other economic factors, which are determined based on current market conditions. The following table represents the activity for LSRs and the related fair value changes: (Dollars in thousands) Commercial Real Estate Mortgage Total For the year ended December 31, 2017 Fair value, beginning of period $ 344 $ 47,741 $ 48,085 Transfers in based on new accounting policy election — 15,891 15,891 Additions from loans sold with servicing retained 188 8,557 8,745 Changes in fair value due to: Reductions from pay-offs, pay downs and run-off (105 ) (2,400 ) (2,505 ) Changes in estimates of fair value (1) — (6,375 ) (6,375 ) Fair value, end of period $ 427 $ 63,414 $ 63,841 Principal balance of loans serviced $ 40,316 $ 7,068,431 $ 7,108,747 For the year ended December 31, 2016 Fair value, beginning of period $ — $ — $ — Acquired in Talmer Bancorp, Inc. merger 365 42,097 42,462 Additions from loans sold with servicing retained — 1,030 1,030 Changes in fair value due to: Reductions from pay-offs, pay downs and run-off (17 ) (502 ) (519 ) Changes in estimates of fair value (1) (4 ) 5,116 5,112 Fair value, end of period $ 344 $ 47,741 $ 48,085 Principal balance of loans serviced under the fair value measurement method $ 64,756 $ 5,235,415 $ 5,300,171 (1) Represents estimated LSR value change resulting primarily from market-driven changes in interest rates and prepayments. Included in "Net gain on sale of loans and other mortgage banking revenue" in the Consolidated Statements of Income. The following shows the net carrying value and fair value of LSRs and the total loans that the Corporation serviced for others accounted for at the lower of cost or fair value for the years ended December 31, 2016 and 2015: Years Ended December 31, (Dollars in thousands) 2016 2015 Net carrying value of LSRs $ 10,230 $ 11,122 Fair value of LSRs $ 15,891 $ 15,542 Valuation allowance $ 8 $ — Loans serviced for others that have servicing rights capitalized $ 2,074,057 $ 2,082,899 Activity for LSRs accounted for at the lower of cost or fair value and the related valuation allowance for the years ended December 31, 2016 and 2015 are as follows: Years Ended December 31, (Dollars in thousands) 2016 2015 Balance at beginning of period $ 11,122 $ 12,217 Acquired through acquisitions — 1,284 Additions 3,303 1,476 Amortization (4,187 ) (4,055 ) Change in valuation allowance (8 ) 200 Balance at end of period $ 10,230 $ 11,122 Expected and actual loan prepayment speeds are the most significant factors driving the fair value of loan servicing rights. The following table presents assumptions utilized in determining the fair value of loan servicing rights as of December 31, 2017 and 2016 . Mortgage As of December 31, 2017 Prepayment speed 0.00 - 38.8% Weighted average ("WA") discount rate 10.1 % Cost to service/per year $ 66 WA Ancillary income/per year $ 31 WA float range 1.6 % As of December 31, 2016 Prepayment speed 0.00 - 99.8% WA discount rate 10.1 % Cost to service/per year $65-$90 Ancillary income/per year $ 28 WA float range 1.0 % The Corporation realized total loan servicing fee income of $18.2 million , $8.7 million and $5.4 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, recorded as a component of "Net gain on sale of loans and other mortgage banking revenue" in the Consolidated Statements of Income.

Derivative Instruments and Bala

Derivative Instruments and Balance Sheet Offsetting	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Balance Sheet Offsetting	Derivative Instruments and Balance Sheet Offsetting In the normal course of business, the Corporation enters into various transactions involving derivative instruments to manage exposure to fluctuations in interest rates and to meet the financing needs of customers (customer-initiated derivatives). These financial instruments involve, to varying degrees, elements of market and credit risk. Market and credit risk are included in the determination of fair value. Commitments to fund mortgage loans (interest rate locks) to be sold into the secondary market and forward commitments for the future delivery of mortgage loans to third party investors are considered derivatives. It is the Corporation’s practice to enter into forward commitments for the future delivery of mortgage loans when interest rate lock commitments are entered into in order to economically hedge the effect of changes in interest rates resulting from its commitments to fund the loans. The Corporation enters into interest rate derivatives to provide a service to certain qualifying customers to help facilitate their respective risk management strategies, customer-initiated derivatives, and, therefore, are not used for interest rate risk management purposes. These derivatives primarily consist of interest rate swaps, interest rate caps and floors, and foreign exchange contracts. The Corporation generally takes offsetting positions with dealer counterparts to mitigate the inherent risk. Income primarily results from the spread between the customer derivative and the offsetting dealer positions. Gains and losses on customer-related derivatives are included in other noninterest income. The Corporation utilizes interest rate swaps for risk management purposes to manage exposures that arise from business activities that result in the receipt or payment of future known and uncertain cash amounts, the value of which are determined by interest rates. These interest rate swaps designated as cash flow hedges are used to manage differences in the amount, timing and duration of the Corporation's known or expected cash receipts and its known or expected cash payments principally related to certain variable rate borrowings. The Corporation assesses the effectiveness of each hedging relationship by comparing the changes in cash flows of the derivative instruments with the changes in cash flows of the designated hedged transactions. The effective portion of changes in fair value of derivatives designated and that qualify as cash flow hedges is recorded in accumulated other comprehensive income (loss) and is subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. Any ineffective portion of the change in fair value of the derivatives is recognized directly in earnings. The Corporation expects the hedges to remain highly effective during the remaining terms of the swaps. The Corporation additionally has written and purchased option derivatives consisting of instruments to facilitate an equity-linked time deposit product (the "Power Equity CD"). The Power Equity CD is a time deposit that provides the purchaser a guaranteed return of principal at maturity plus a potential equity return (a written option), while the Corporation receives a known stream of funds based on the equity return (a purchased option). The written and purchased options are mirror derivative instruments which are carried at fair value on the Consolidated Statements of Financial Position. The following table presents the notional amount and fair value of the Corporation’s derivative instruments held or issued in connection with customer-initiated and mortgage banking activities. December 31, 2017 2016 Fair Value Fair Value (Dollars in thousands) Notional Amount (1) Gross Derivative Assets (2) Gross Derivative Liabilities (2) Notional Amount (1) Gross Derivative Assets (2) Gross Derivative Liabilities (2) Risk management purposes: Derivatives designated as hedging instruments: Interest rate swaps $ 620,000 $ 5,899 $ — $ — $ — $ — Total risk management purposes 620,000 5,899 — — — — Customer-initiated and mortgage banking derivatives: Customer-initiated derivatives 1,365,119 9,376 10,139 600,598 4,406 4,141 Foreign exchange forwards (3) — — — — — — Forward contracts related to mortgage loans to be delivered for sale 115,996 — 34 140,155 635 — Interest rate lock commitments 71,003 1,222 — 76,034 956 — Power Equity CD 38,807 2,184 2,184 36,807 2,218 2,218 Total customer-initiated and mortgage banking derivatives 1,590,925 12,782 12,357 853,594 8,215 6,359 Total gross derivatives $ 2,210,925 $ 18,681 $ 12,357 $ 853,594 $ 8,215 $ 6,359 (1) Notional or contract amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the Consolidated Statements of Financial Position. (2) Derivative assets are included within "Interest receivable and other assets" and derivative liabilities are included within "Interest Payable and other liabilities" on the Consolidated Statements of Financial Position. Included in the fair value of the derivative assets are credit valuation adjustments for counterparty credit risk totaling $809 thousand at December 31, 2017 and $99 thousand at December 31, 2016 . (3) The foreign exchange forwards that were entered into during the year ended December 31, 2017 had matured as of December 31, 2017 . In the normal course of business, the Corporation may decide to settle a forward contract rather than fulfill the contract. Cash received or paid in this settlement manner is included in "Net gain (loss) on sale of loans and other mortgage banking revenue" in the Consolidated Statements of Income and is considered a cost of executing a forward contract. The following table presents the net gains (losses) related to derivative instruments reflecting the changes in fair value. For the years ended December 31, (Dollars in thousands) Location of Gain (Loss) 2017 2016 2015 Forward contracts related to mortgage loans to be delivered for sale Net gain (loss) on sale of loans and other mortgage banking revenue $ (669 ) $ 692 $ 193 Interest rate lock commitments Net gain (loss) on sale of loans and other mortgage banking revenue 266 (1,356 ) (132 ) Customer-initiated derivatives Other noninterest income (1,028 ) 581 — Total gain (loss) recognized in income $ (1,431 ) $ (83 ) $ 61 The following table presents the net gains (losses) recorded in accumulated other comprehensive income and the Consolidated Statements of Income relating to interest rate swaps designated as cash flow hedges for the year ended December 31, 2017 . The Corporation first began entering into interest rate swaps designated as cash flow hedges during the year ended December 31, 2017. (Dollars in thousands) Amount of gain (loss) recognized in other comprehensive income (Effective portion) Amount of gain (loss) reclassified from other comprehensive income to interest income or expense (Effective portion) Amount of gain (loss) recognized in other noninterest income (Ineffective portion) Year Ended December 31, 2017 Interest rate swaps designated as cash flow hedges $ 4,263 $ (1,633 ) $ (3 ) At December 31, 2017 , the Corporation expected $0.3 million of unrealized income to be reclassified as a decrease to interest expense during the following twelve months. Methods and assumptions used by the Corporation in estimating the fair value of its forward contracts, interest rate lock commitments and customer-initiated derivatives are discussed in Note 3. Balance Sheet Offsetting Certain financial instruments, including customer-initiated derivatives and interest rate swaps, may be eligible for offset in the Consolidated Statements of Financial Position and/or subject to master netting arrangements or similar agreements. The Corporation is party to master netting arrangements with its financial institution counterparties; however, the Corporation does not offset assets and liabilities under these arrangements for financial statement presentation purposes based on an accounting policy election. The tables below present information about the Corporation’s financial instruments that are eligible for offset. Gross amounts not offset in the (Dollars in thousands) Gross Gross amounts Net amounts Financial Collateral Net December 31, 2017 Offsetting derivative assets Derivative assets $ 15,228 $ — $ 15,228 $ — $ — $ 15,228 Offsetting derivative liabilities Derivative liabilities 10,139 — 10,139 — 1,081 9,058 December 31, 2016 Offsetting derivative assets Derivative assets $ 4,405 $ — $ 4,405 $ — $ — $ 4,405 Offsetting derivative liabilities Derivative liabilities 4,141 — 4,141 — 2,550 1,591

Other Intangible Assets

Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Other Intangible Assets	Other Intangible Assets The following table shows the net carrying value of the Corporation's other intangible assets. December 31, (Dollars in thousands) 2017 2016 Core deposit intangible assets $ 34,259 $ 40,211 Non-compete intangible assets 12 — Total other intangible assets $ 34,271 $ 40,211 Core Deposit Intangible Assets The Corporation recorded core deposit intangible assets associated with each of its acquisitions. Core deposit intangible assets are amortized on an accelerated basis over their estimated useful lives and have an estimated remaining weighted-average useful life of 7.5 years as of December 31, 2017 . The following table sets forth the carrying amount and accumulated amortization of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions: December 31, (Dollars in thousands) 2017 2016 Gross carrying amount $ 59,143 $ 59,143 Accumulated amortization 24,884 18,932 Net carrying amount $ 34,259 $ 40,211 Amortization expense recognized on core deposit intangible assets was $6.0 million , $5.2 million and $4.1 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The estimated future amortization expense on core deposit intangible assets for the next five years is as follows: (Dollars in thousands) Estimated amortization expense 2018 $ 5,703 2019 5,441 2020 4,850 2021 4,471 2022 4,218

Commitments, Contingencies and

Commitments, Contingencies and Guarantees	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies and Guarantees	Commitments, Contingencies and Guarantees Commitments In the normal course of business, the Corporation offers a variety of financial instruments containing credit risk that are not required to be reflected in the Consolidated Statements of Financial Position. These financial instruments include outstanding commitments to extend credit, approved but undisbursed loans (undisbursed loan commitments), credit lines, commercial letters of credit and standby letters of credit. The Corporation has risk management policies to identify, monitor and limit exposure to credit risk. To mitigate credit risk for these financial guarantees, the Corporation generally determines the need for specific covenant, guarantee and collateral requirements on a case-by-case basis, depending on the nature of the financial instrument and the customer's creditworthiness. At December 31, 2017 and 2016 , the Corporation had $187.6 million and $118.9 million , respectively, of outstanding financial and performance standby letters of credit. The majority of these standby letters of credit are collateralized. The Corporation determined that there were no potential losses from standby letters of credit at December 31, 2017 and 2016 . Commitments to extend credit are agreements to lend to a customer provided there is no violation of any condition established in the commitment. Commitments generally have fixed expiration dates or other termination clauses and may not require payment of a fee. Since many commitments expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Corporation evaluates each customer's creditworthiness on an individual basis. The amount of collateral obtained, if deemed necessary by the Corporation upon extension of credit, is based on management's credit evaluation of the counterparty. The collateral held varies, but may include securities, real estate, accounts receivable, inventory, plant or equipment. Unfunded commitments under commercial lines of credit, revolving credit lines and overdraft protection agreements are included in commitments to extend credit. These lines of credit are generally not collateralized, usually do not contain a specified maturity date and may be drawn upon only to the total extent to which the Corporation is committed. At December 31, 2017 and 2016 , the Corporation had $3.03 billion and $2.70 billion , respectively, of commitments to extend credit. The Corporation had undisbursed loan commitments of $571.0 million and $578.2 million at December 31, 2017 and 2016 , respectively. Undisbursed loan commitments are not included in loans on the Consolidated Statements of Financial Position. The majority of undisbursed loan commitments will be funded and convert to a portfolio loan within a one year period. The allowance for credit losses on lending-related commitments included $1.2 million and $1.3 million at December 31, 2017 and 2016 , respectively, for probable credit losses inherent in the Corporation's unused commitments and was recorded in "Interest payable and other liabilities" in the Consolidated Statements of Financial Position. Contingencies and Guarantees The Corporation has originated and sold certain loans, and additionally acquired the potential liability for those historical originated and sold loans by Talmer, for which the buyer has limited recourse to us in the event the loans do not perform as specified in the agreements. These loans had an outstanding balance of $13.3 million and $16.9 million at December 31, 2017 and 2016 , respectively. The maximum potential amount of undiscounted future payments that the Corporation could be required to make in the event of nonperformance by the borrower totaled $12.8 million and $16.1 million at December 31, 2017 and 2016 , respectively. In the event of nonperformance, the Corporation has rights to the underlying collateral securing the loans. At both December 31, 2017 and 2016 , the Corporation had recorded a liability of $0.2 million , in connection with the recourse agreements, recorded in "Interest payable and other liabilities" in the Consolidated Statements of Financial Position. Representations and Warranties In connection with the Corporation's mortgage banking loan sales, and the historical sales of merged or acquired entities, the Corporation makes certain representations and warranties that the loans meet certain criteria, such as collateral type and underwriting standards. The Corporation may be required to repurchase individual loans and/or indemnify the purchaser against losses if the loan fails to meet established criteria. At December 31, 2017 and 2016 , respectively, the liability recorded in connection with these representations and warranties totaled $5.3 million and $6.5 million , respectively. A summary of the reserve for representations and warranties of the Corporation is as follows: For the years ended December 31, (Dollars in thousands) 2017 2016 2015 Reserve balance at beginning of period $ 6,459 $ 4,048 $ 3,000 Addition of fair value of representations and warranties due to mergers and acquisitions — 3,100 1,712 Reserve reduction (1,095 ) (580 ) — Charge-offs (15 ) (109 ) (664 ) Ending reserve balance $ 5,349 $ 6,459 $ 4,048 Reserve balance: Liability for specific claims 531 730 — General allowance 4,818 5,729 4,048 Total reserve balance $ 5,349 $ 6,459 $ 4,048 Operating Leases and Other Noncancelable Contractual Obligations The Corporation has operating leases and other noncancelable contractual obligations on buildings, equipment, computer software and other expenses that will require annual payments through 2034 , including renewal option periods for those building leases that the Corporation expects to renew. Future minimum lease payments for operating leases and other noncancelable contractual obligations are as follows: (Dollars in thousands) Future Minimum Lease Payments (1) Years ending December 31, 2018 $ 22,973 2019 21,487 2020 18,808 2021 16,794 2022 20,112 Thereafter 33,775 Total $ 133,949 (1) Future minimum lease payments are reduced by $0.9 million related to sublease income to be received within the next five years. Minimum payments include estimates, where applicable, of estimated usage and annual Consumer Price Index increases of approximately 2.1% . Total expense recorded under operating leases and other noncancelable contractual obligations was $30.8 million in 2017 , compared to $20.4 million in 2016 and $15.6 million in 2015 . Legal Proceedings The Corporation and Chemical Bank are subject to various pending or threatened legal proceedings arising out of the normal course of business and related to our merger and acquisition history. The Corporation assesses its liabilities and contingencies in connection with outstanding legal proceedings utilizing the latest information available. Where it is probable that the Corporation will incur a loss and the amount of the loss can be reasonably estimated, the Corporation records a liability in the Consolidated Financial Statements. While the ultimate liability with respect to these litigation matters and claims cannot be determined at this time, in the opinion of management, the ultimate disposition of these matters is not expected to have a material adverse effect on the financial position or results of operations of the Corporation.

Investments in Qualified Afford

Investments in Qualified Affordable Housing Projects, Federal Historic Projects and New Market Tax Credits	12 Months Ended
	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Investments in Qualified Affordable Housing Projects, Federal Historic Projects and New Market Tax Credits	Investments in Qualified Affordable Housing Projects, Federal Historic Projects and New Market Tax Credits The Corporation invests in qualified affordable housing projects, federal historic projects, and new market projects for the purpose of community reinvestment and obtaining tax credits. Return on the Corporation's investment in these projects comes in the form of the tax credits and tax losses that pass through to the Corporation. The carrying value of the investments is reflected in "Interest receivable and other assets" on the Consolidated Statements of Financial Position. The Corporation utilizes the proportional amortization method to account for investments in qualified affordable housing projects and the equity method to account for investments in other tax credit projects. Under the proportional amortization method, the Corporation amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits. The Corporation recognized additional income tax expense attributable to the amortization of investments in qualified affordable housing projects of $3.4 million , $2.6 million and $1.3 million during the years ended December 31, 2017 , 2016 and 2015 , respectively. The Corporation's remaining investment in qualified affordable housing projects accounted for under the proportional amortization method totaled $51.4 million at December 31, 2017 and $29.5 million at December 31, 2016 . Under the equity method, the Corporation's share of the earnings or losses is included in "Other operating expenses" on the Consolidated Statements of Income. The Corporation's remaining investment in new market projects accounted for under the equity method totaled $17.3 million and $10.9 million at December 31, 2017 and 2016 , respectively. The Corporation's unfunded equity contributions relating to investments in qualified affordable housing projects, federal historic tax projects and new market projects is recorded in "Interest payable and other liabilities" on the Consolidated Statements of Financial Position. The Corporation's remaining unfunded equity contributions totaled $48.1 million and $16.0 million at December 31, 2017 and 2016 , respectively. Management analyzes these investments for potential impairment when events or changes in circumstances indicate that it is more-likely-than-not that the carrying amount of the investment will not be realized. An impairment loss is measured as the amount by which the carrying amount of an investment exceeds its fair value. During the year ended December 31, 2017 , multiple federal housing tax credits were placed into service resulting in income tax benefit of $7.9 million , partially offset by i mpairment expense of $9.3 million , $6.0 million net of tax, recorded in "other noninterest expense." There was no impairment losses recognized as of December 31, 2016 . The Corporation consolidates variable interest entities ("VIEs") in which it is the primary beneficiary. In general, a VIE is an entity that either (i) has an insufficient amount of equity to carry out its principal activities without additional subordinated financial support, (ii) has a group of equity owners that are unable to make significant decisions about its activities or (iii) has a group of equity owners that do not have the obligation to absorb losses or the right to receive returns as generated by its operations. If any of these characteristics are present, the entity is subject to a variable interest consolidation model, and consolidation is based on variable interests, not on ownership of the entity's outstanding voting stock. Variable interests are defined as contractual, ownership, or other monetary interests in an entity that change with fluctuations in the entity's net asset value. The primary beneficiary consolidates the VIE. The primary beneficiary is defined as the enterprise that has the power to direct the activities and absorb losses or the right to receive benefits. The Corporation is a significant limited partner in the qualified affordable housing, federal historic and new market projects it has invested in . These projects meet the definition of VIEs. However, the Corporation is not the primary beneficiary of any of the VIEs in which it holds a limited partnership interest; therefore, the VIEs are not consolidated in the Consolidated Financial Statements.

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposits	Deposits A summary of deposits follows: December 31, (Dollars in thousands) 2017 2016 Noninterest-bearing demand $ 3,725,779 $ 3,341,520 Savings 1,697,762 1,662,115 Interest-bearing demand 2,724,415 2,825,801 Money market accounts 1,957,909 2,033,319 Brokered deposits 453,227 226,429 Other time deposits 3,083,711 2,783,938 Total deposits $ 13,642,803 $ 12,873,122 Excluded from total deposits are demand deposit account overdrafts (overdrafts) which have been classified as loans. At December 31, 2017 and 2016 , overdrafts totaled $5.9 million and $5.0 million , respectively. Deposits from executive officers, directors, principal shareholders and their related interests were $10.6 million at December 31, 2017 . Time deposits, including certificates of deposit and certain individual retirement account deposits, of $250 thousand or more totaled $1.6 billion and $975.4 million at December 31, 2017 and 2016 , respectively. At December 31, 2017 , the scheduled maturities of time deposits for the next five years were as follows: (Dollars in thousands) 2018 $ 2,168,858 2019 646,514 2020 183,101 2021 134,806 2022 81,169 Thereafter 2,759 Total $ 3,217,207

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Borrowings	Borrowings A summary of the Corporation's short- and long-term borrowings follows: December 31, 2017 2016 (Dollars in thousands) Amount Weighted Average Rate (1) Amount Weighted Average Rate (1) Securities sold under agreements to repurchase with customers: Securities sold under agreements to repurchase with customers $ 415,236 0.44 % $ 343,047 0.16 % Short-term borrowings: FHLB advances: 1.25% - 1.50% fixed-rate notes 2,000,000 1.39 825,000 0.65 Long-term borrowings: FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020 (2) 337,204 1.26 438,538 1.24 Securities sold under agreements to repurchase (3) — — 19,144 3.17 Line-of-credit: floating-rate based on one-month LIBOR plus 1.75% 19,963 3.10 124,625 2.52 Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 (4) 11,425 3.69 11,285 3.14 Subordinated debt obligations: floating-rate based on three-month LIBOR plus 3.25% due in 2032 (5) 4,290 4.59 4,255 4.25 Total long-term borrowings 372,882 1.47 597,847 1.63 Total short-term and long-term borrowings $ 2,788,118 1.26 % $ 1,765,894 0.89 % (1) Weighted average rate presented is the contractual rate which excludes premiums and discounts related to purchase accounting. (2) The December 31, 2017 balance includes advances payable of $337.0 million and purchase accounting premiums of $0.2 million . The December 31, 2016 balance includes advances payable of $437.8 million and purchase accounting premiums of $0.7 million . (3) The December 31, 2016 balance includes advance payable of $19.0 million and purchase accounting premiums of $0.1 million . (4) The December 31, 2017 balance includes advances payable of $15.0 million and purchase accounting discounts of $3.6 million . The December 31, 2016 balance includes advance payable of $15.0 million and purchase accounting premiums of $3.7 million . (5) The December 31, 2017 balance includes advances payable of $5.0 million and purchase accounting discounts of $0.7 million . The December 31, 2016 balance includes advance payable of $5.0 million and purchase accounting premiums of $0.7 million . Chemical Bank is a member of the FHLB, which provides short- and long-term funding collateralized by mortgage related assets to its members. Each advance is payable at its maturity date, with a prepayment penalty for fixed-rate advances. The Corporation's FHLB advances, including both short-term and long-term, require monthly interest payments and are collateralized by commercial and residential mortgage loans totaling $7.36 billion as of December 31, 2017 . The Corporation's additional borrowing availability through the FHLB, subject to the FHLB's credit requirements and policies and based on the amount of FHLB stock owned by the Corporation, was $193.5 million at December 31, 2017 . In conjunction with the merger with Talmer, the Corporation entered into a credit agreement of $145.0 million consisting of a $125.0 million term line-of credit and a $20.0 million revolving line-of-credit. The Corporation drew $125.0 million on the term line-of-credit to pay off the Corporation's prior $25.0 million line-of-credit and a $37.5 million line-of-credit acquired in the merger with Talmer, with the remaining proceeds used to partially fund the cash portion of the merger consideration. The line-of-credit agreement contains covenants related to certain thresholds that must be maintained related to the nonperforming assets to tangible capital ratio, the loan loss reserve to nonperforming loan ratio, the liquidity ratio and return on average assets. The Corporation was in compliance with all of the covenants at December 31, 2017 . At December 31, 2017 , the contractual principal payments due and the amortization/accretion of purchase accounting adjustments for the remaining maturities of long-term debt over the next five years and thereafter are as follows: (Dollars in thousands) Long-term Debt by Maturity Years Ending December 31, 2018 $ 147,065 2019 100,058 2020 110,044 2021 — 2022 — Thereafter 15,715 Total $ 372,882

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The current and deferred components of the provision for income taxes were as follows: Years Ended December 31, (Dollars in thousands) 2017 2016 2015 Current income tax expense (benefit) Federal $ 14,665 $ 19,144 $ 31,300 State 20 (423 ) — Total current income tax expense 14,685 18,721 31,300 Deferred expense (benefit) Federal 92,636 23,649 5,700 State 548 442 — Total deferred income tax expense (benefit) 93,184 24,091 5,700 Change in valuation allowance (1,089 ) (706 ) — Income tax provision $ 106,780 $ 42,106 $ 37,000 A reconciliation of expected income tax expense at the federal statutory income tax rate and the amounts recorded in the Consolidated Financial Statements were as follows: Years Ended December 31, 2017 2016 2015 (Dollars in thousands) Amount Rate Amount Rate Amount Rate Tax at statutory rate $ 89,706 35.0 % $ 52,548 35.0 % $ 43,341 35.0 % Changes resulting from: Tax-exempt interest income (9,001 ) (3.5 ) (5,320 ) (3.5 ) (3,943 ) (3.2 ) State taxes, net of federal benefit 369 0.1 13 — — — Change in valuation allowance (1,089 ) (0.4 ) (706 ) (0.5 ) — — Bank-owned life insurance adjustments (1,696 ) (0.7 ) (832 ) (0.6 ) (124 ) (0.1 ) Director plan change in control — — (508 ) (0.3 ) — — Income tax credits, net (11,449 ) (4.4 ) (2,454 ) (1.6 ) (2,557 ) (2.1 ) Nondeductible transaction expenses 156 0.1 2,100 1.4 411 0.3 Tax benefits in excess of compensation costs on share-based payments (1) (5,886 ) (2.3 ) (2,240 ) (1.5 ) — — Impact of the Tax Cuts and Jobs Act (2) 46,660 18.2 — — — — Other, net (990 ) (0.4 ) (495 ) (0.4 ) (128 ) — Income tax expense $ 106,780 41.7 % $ 42,106 28.0 % $ 37,000 29.9 % (1) The years ended December 31, 2017 and 2016 reflect the adoption of ASU 2016-09, as of January 1, 2016, which results in excess tax benefits recognized within "Income tax expense" rather than previously recognized directly into equity with "Additional paid-in-capital." Refer to Note 1, Summary of Significant Accounting Policies, for further details. (2) The year ended December 31, 2017 included the impact of the enactment of H.R.1 (the "Tax Cuts and Jobs Act"), which required a revaluation of net deferred tax assets and liabilities, see below for further details. On December 22, 2017, H.R.1 (known as the "Tax Cuts and Jobs Act") was signed into law. Among other provisions, the Tax Cuts and Jobs Act, reduces the statutory corporate income tax rate from a maximum rate of 35% to flat tax rate of 21% , effective January 1, 2018. ASC Topic 740 requires the recognition of the effects of tax law changes be recorded in the period in which the law is enacted. Therefore, the Corporation's deferred tax assets and liabilities which were previously valued at a federal rate of 35% , were revalued to the current enacted federal tax rate of 21% . The impact of the Tax Cuts and Jobs Act resulted in a $46.7 million increase to income tax expense related to continuing operations as a result of the revaluation of the net deferred tax asset of $46.0 million and an acceleration of amortization expense on the low income housing tax credit investment portfolio of $0.7 million . The SEC issued Staff Accounting Bulletin No. 118 to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available in reasonable detail to complete the accounting for certain income tax effects of the Tax Cuts and Jobs Act, thereby allowing a measurement period to reflect provisional adjustments as information becomes available. The measurement period includes the Tax Cuts and Jobs Acts' enactment date up until one year after. The Corporation does not have any provisional adjustments to its net deferred tax asset as a result of the tax reform at December 31, 2017 under Staff Accounting Bulletin No. 118, but the Corporation will have adjustments in 2018 to reflect the impact of the rate reduction on various deferred items that management reasonably estimated at December 31, 2017 and will true up with the filing of the 2017 tax return in 2018. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The significant components of the deferred tax assets and liabilities at December 31, 2017 and 2016 were as follows: December 31, (Dollars in thousands) 2017 2016 Deferred tax assets: Allowance for loan losses $ 20,446 $ 45,763 Acquisition-related fair value adjustments 27,607 54,704 Accrued stock-based compensation 4,082 18,891 Loss and tax credit carry forwards 57,969 76,446 Depreciation 2,954 11,270 Nonaccrual loan interest 6,155 9,465 Accrued expense 9,200 20,858 Other 9,127 15,751 Total deferred tax assets 137,540 253,148 Deferred tax liabilities: Loan servicing rights 13,446 20,450 Core deposit intangible assets 6,022 11,844 Goodwill 4,076 6,373 Prepaid expenses 7,390 4,873 Other 7,735 2,762 Total deferred tax liabilities 38,669 46,302 Net deferred tax asset before valuation allowance 98,871 206,846 Valuation allowance (1,150 ) (2,239 ) Net deferred tax asset $ 97,721 $ 204,607 On August 31, 2016, the Corporation merged with Talmer and recorded $151.9 million in deferred tax assets, net of valuation allowance. In connection with the merger, Talmer incurred an ownership change within the meaning of Section 382 of the Internal Revenue Code ("IRC"). At August 31, 2016, Talmer had $102.8 million in gross federal net operating loss carry forwards, $88.7 million in gross realized built-in loss carry forwards, $1.0 million in federal tax credit carry forwards that expire from 2026 through 2035, and $14.9 million in federal alternative minimum tax credits with an indefinite life. The valuation allowance against the Corporation’s deferred tax assets at December 31, 2017 totaled $1.2 million and included $0.6 million due to IRC Section 382 limitations on the utilization of pre-ownership change loss and tax credit carry forwards associated with Talmer’s previously acquired entities and $0.6 million due to management’s estimate of capital loss carry forwards more likely than not to expire unutilized. Actual outcomes could vary from the Corporation's current estimates, resulting in future increases or decreases in the valuation allowance and corresponding future tax expense or benefit. Due to the substantial equity value of Talmer at the time of the ownership change, the entity was deemed to be in a net unrealized built-in gain position which allows for the utilization of certain carry forward attributes. Therefore, no additional valuation allowance was established against Talmer's net deferred tax assets. The following table is a summary of the loss attributes, Section 382 limitations, and tax expiration periods as of December 31, 2017 . From the Acquisition of: Talmer's Prior Ownership Changes (Dollars in thousands) Talmer Monarch First Place Holdings/First Place Bank Talmer West Bank First of Huron Corp./Signature Bank From 2009 Ownership change Not Limited by Section 382 Total Tax Loss and Credit Carryforwards as of 12/31/17: Years Expiring (except AMT Credits) 2032-2034 2026-2034 2027-2031 2028-2032 2029-2032 2027-2029 2036 Annual Section 382 limitation-base (1) $ 34,668 $ 673 $ 6,650 $ 3,028 $ 365 $ 145 $ — $ N/A Gross Federal Net Operating Losses — 15,047 — 47,284 649 1,740 — 64,720 Gross Capital Losses — — — — — — — — Realized Built-in Losses — — 68,356 8,936 — — — 77,292 Business Tax Credits 170 1,651 781 — — — 912 3,514 Less amounts not recorded due to Sec 382 Limitation — (1,738 ) (65 ) (3,218 ) — (145 ) — (5,166 ) Alternative Minimum Tax Credits - no expiration 12,473 106 2,115 — 303 — 10,832 25,829 Valuation Allowance — — — (585 ) — — (565 ) (1,150 ) (1) In respect to the Monarch and Talmer acquisitions, in addition to the statutory "base" Section 382 limitation, recognized built in gain increases the Section 382 limitation during the five year period beginning on the acquisition date. The Corporation estimates that the recognized built in gain will total $2.8 million and $253.2 million for the Monarch and Talmer acquisitions, respectively. Management concluded that no valuation allowance was necessary on the remainder of the Corporation's net deferred tax assets at December 31, 2017 and 2016 . This determination was based on the Corporation's history of pre-tax and taxable income over the prior three years, as well as management's expectations for sustainable profitability in the future. Management monitors deferred tax assets quarterly for changes affecting the ability to realize and the valuation allowance could be adjusted in future periods. At December 31, 2017 , the Corporation had approximately $36.0 million of bad debt reserve in equity for which no provision for federal income taxes was recorded. This amount represents Talmer's qualifying thrift bad debt reserve at December 31, 1987 through its acquisition of First Place Bank, which is only required to be recaptured into taxable income if certain events occur. At December 31, 2017 , the potential tax on the above amount was approximately $7.5 million . The Corporation does not intend to take any action that would result in a recapture of any portion of its bad debt reserve. The Corporation's federal tax return for the years ended December 31, 2014 to present are open to potential examination. Talmer amended its four federal tax returns for the years 2011, 2012, 2013 and 2014 to reflect the impact of changes to First Place Bank due to an IRS settlement in January of 2016. These four amendments were selected for audit which concluded with no changes and all expected refunds were received in 2017.The Corporation's most significant states of operation, Michigan and Ohio, do not impose income-based taxes on financial institutions. The Corporation and/or its subsidiaries are subject to immaterial amounts of income tax in various other states, with varying years open to potential examination. The Corporation received notice in February 2018 that Talmer Bancorp's Ohio Financial Institutions tax has been selected for audit for the years ended December 31, 2013, 2014 and 2015. The Corporation had no unrecognized tax benefits at December 31, 2017 or 2016 and does not expect to record unrecognized tax benefits of any significance during the next twelve months. The Corporation recognizes interest and/or penalties related to income tax matters in income tax expense, when applicable. There were no liabilities accrued for interest and/or penalties at December 31, 2017 or 2016 .

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation The Corporation maintains share-based compensation plans under which it periodically grants share-based awards for a fixed number of shares to certain officers of the Corporation. The fair value of share-based awards is recognized as compensation expense over the requisite service or performance period. During the years ended December 31, 2017 , 2016 and 2015 , share-based compensation expense related to share-based awards totaled $17.3 million , $14.7 million and $3.7 million , respectively. The excess tax benefit realized from shared-based compensation transactions during the years ended December 31, 2017 , 2016 and 2015 was $6.1 million , $2.2 million and $0.5 million , respectively. During the year ended December 31, 2017 , the Corporation granted options to purchase 132,414 shares of common stock, 169,252 restricted stock units and 72,537 shares of common stock to certain officers of the Corporation. On April 26, 2017, the shareholders of the Corporation approved the Stock Incentive Plan of 2017, which provides for 1,750,000 shares of the Corporation's common stock to be made available for future equity-based awards and canceled the amount of shares available for future grant under prior share-based compensation plans. At December 31, 2017 , there were 1,681,101 shares of common stock available for future grants under the Stock Incentive Plan of 2017. Stock Options The Corporation issues stock options to certain officers from time to time. The exercise price on stock options equals the current market price of the Corporation's common stock on the date of grant and stock options expire ten years from the date of grant. Stock options granted after 2012 vest ratably over a five -year period. Stock options granted prior to 2013 generally vest ratably over a three -year period. Stock options granted prior to 2016 fully vested upon completion of the merger with Talmer. Stock options assumed by the Corporation in the merger with Talmer were fully vested prior to assumption. The following summarizes information about stock options outstanding and exercisable at December 31, 2017 : Options outstanding Options exercisable Range of exercise prices per share Number outstanding Weighted average exercise price per share Weighted average contractual term (in years) Number exercisable Weighted average exercise price per share Weighted average contractual term (in years) $11.09 - 12.80 32,691 $ 12.37 2.93 32,691 $ 12.37 2.93 $13.20 - 16.24 136,604 15.94 4.92 136,604 15.94 4.92 $19.97 - 21.10 49,546 20.36 2.62 49,546 20.36 2.62 $23.78 - 25.14 232,582 24.56 4.33 232,582 24.56 4.33 $29.45 - 32.81 537,893 31.68 7.62 290,534 30.72 7.15 $46.95 - 53.72 121,602 53.40 9.25 38,091 53.72 9.23 $11.09 - 53.72 1,110,918 $ 29.56 6.42 780,048 $ 25.99 5.56 The intrinsic value of all outstanding in-the-money stock options and exercisable in-the-money stock options was $26.6 million and $21.4 million , respectively, at December 31, 2017 . The aggregate intrinsic values of outstanding and exercisable options at December 31, 2017 were calculated based on the closing market price of the Corporation's common stock on December 31, 2017 of $53.47 per share less the exercise price. Options with intrinsic values less than zero, or "out-of-the-money" options, are not included in the aggregate intrinsic value reported. The total intrinsic value of stock options for the years ended December 31, 2016 and 2015 was $80.4 million and $7.6 million , respectively. A summary of activity for the Corporation's stock options as of and during the years ended December 31, 2017 , 2016 and 2015 is presented below: Non-vested stock options outstanding Stock options outstanding Number of options Weighted- average exercise price per share Weighted- average grant date fair value per share Number of options Weighted- average exercise price per share Outstanding at December 31, 2014 432,199 $ 26.75 $ 8.30 1,037,311 $ 25.90 Granted 244,165 30.18 8.40 244,165 30.18 Acquired — — — 132,883 12.93 Exercised — — — (310,985 ) 25.10 Vested (150,224 ) 25.57 7.80 — — Forfeited/expired (46,385 ) 27.99 8.50 (48,635 ) 28.18 Outstanding at December 31, 2015 479,755 $ 28.75 $ 8.49 1,054,739 $ 25.38 Granted 441,167 32.81 6.15 441,167 32.81 Acquired — — — 1,466,408 15.08 Exercised — — — (450,296 ) 20.02 Vested (454,360 ) 28.74 8.49 — — Forfeited/expired (58,623 ) 31.10 7.17 (58,623 ) 31.10 Outstanding at December 31, 2016 407,939 $ 32.81 $ 6.15 2,453,395 $ 21.41 Granted 132,414 53.43 9.94 132,414 53.43 Exercised — — — (1,427,159 ) 17.50 Vested (161,751 ) 37.73 7.07 — — Forfeited/expired (47,732 ) 37.55 7.03 (47,732 ) 37.55 Outstanding at December 31, 2017 330,870 $ 37.97 $ 7.09 1,110,918 $ 29.56 Exercisable/vested at December 31, 2017 780,048 $ 25.99 Total cash received from option exercises during the years ended December 31, 2017 , 2016 and 2015 was $3.2 million , $2.7 million and $2.3 million , respectively, resulting in the issuance of 621,355 shares, 229,055 shares and 134,659 shares, respectively. At December 31, 2017 , unrecognized compensation expense related to stock options totaled $1.9 million and is expected to be recognized over a remaining weighted average period of 3.5 years. The fair value of the stock options granted during the years ended December 31, 2017 , 2016 and 2015 were estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions. 2017 2016 2015 Expected dividend yield 3.31 % 3.30 % 3.50 % Risk-free interest rate 2.05 % 1.39 % 1.78 % Expected stock price volatility 26.7 % 27.9 % 39.1 % Expected life of options — in years 6.0 6.5 7.0 Weighted average fair value of options granted $9.94 $6.15 $8.40 The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant and the expected life of the options granted. Expected stock volatility was based on historical volatility of the Corporation's common stock over the expected life of the option. The expected life of options represents the period of time that options granted are expected to be outstanding and is based primarily upon historical experience, including option exercise behavior. Because of the unpredictability of the assumptions required, the Black-Scholes (or any other valuation) model is incapable of accurately predicting the Corporation's common stock price or of placing an accurate present value on options to purchase its stock. In addition, the Black-Scholes model was designed to approximate value for types of options that are very different from those issued by the Corporation. In spite of any theoretical value that may be placed on a stock option grant, no value is possible under options issued by the Corporation without an increase in the market price per share of the Corporation's common stock over the market price per share of the Corporation's common stock at the date of grant. Restricted Stock Units The Corporation grants Performance-Based Restricted Stock Units ("PRSUs") and Time-Based Restricted Stock Units ("TRSUs") (collectively referred to as RSUs) to certain officers from time to time. The PRSUs vest based on the Corporation achieving certain performance target levels and the grantee completing the requisite service period. The PRSUs are eligible to vest from 0.5 x to 1.5 x the number of units originally granted depending on which, if any, of the performance target levels are met. However, if the minimum performance target levels are not achieved, no shares will become vested or be issued for that respective year's PRSUs. The TRSUs vest upon satisfaction of a service condition. Upon achievement of the performance target level and/or satisfaction of a service condition, as applicable, the RSUs are converted into shares of the Corporation's common stock on a one-to-one basis. Compensation expense related to RSUs is recognized over the expected requisite performance or service period, as applicable. A summary of the activity for RSUs during the year ended December 31, 2017 is presented below: Number of units Weighted-average grant date fair value per unit Outstanding at December 31, 2016 298,357 $ 32.81 Granted 169,252 51.93 Converted into shares of common stock (75,639 ) 30.73 Forfeited/expired (11,030 ) 47.62 Outstanding at December 31, 2017 380,940 $ 41.29 At December 31, 2017 , unrecognized compensation expense related to RSUs totaled $9.0 million and is expected to be recognized over a remaining weighted average period of 2.7 years . Restricted Stock Awards The Corporation assumed restricted stock awards in the merger with Talmer that vest upon completion of future service requirements. The fair value of these awards is equal to the market price of the Corporation's common stock at the date the awards were assumed with the portion of the fair value related to post-combination service. The Corporation recognizes stock-based compensation expense over the vesting period, using the straight-lined method, based upon the number of shares of restricted stock ultimately expected to vest. If an individual that has been awarded restricted stock awards terminates their employment prior to the end of the vesting period, the unvested portion of the stock is forfeited, with certain exceptions. The following table provides information regarding nonvested restricted stock awards: Nonvested restricted stock awards Number of awards Weighted-average acquisition-date fair value Nonvested at January 1, 2017 365,891 $ 46.23 Vested (277,821 ) 46.23 Forfeited (4,842 ) 46.23 Nonvested at December 31, 2017 83,228 $ 46.23 At December 31, 2017 , unrecognized compensation expense related to nonvested restricted stock awards totaled $2.2 million and is expected to be recognized over a remaining weighted average period of 1.1 years .

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Retirement Plans	Retirement Plans The Corporation's retirement plans include a qualified defined benefit pension plan, a nonqualified pension plan, a nonqualified postretirement benefit plan, a 401(k) savings plan, and a multi-employer defined benefit plan. Qualified Defined Benefit Pension Plan The Chemical Financial Corporation Employees’ Pension Plan (the "Pension Plan") is a qualified defined benefit, noncontributory pension plan, which provides for postretirement pension benefits for certain salaried employees of the Corporation and its subsidiary, Chemical Bank. Benefits under the Pension Plan were partially frozen effective June 30, 2006. Under the partial freeze of the Pension Plan, benefits for employees with less than 15 years of service or whose combined age plus years of service were less than 65 at June 30, 2006, were based on years of vested service at June 30, 2006 and generally the average of the employee's salary for the five years ended June 30, 2006. In addition, no employee hired after January 1, 2006 was eligible to participate in the Pension Plan. Effective September 30, 2017, the Pension and Compensation Committee approved an amendment to the Pension Plan to cease accruing additional benefits under the existing pension benefit formula after the effective date and all accrued benefits were frozen. Retirement benefits under the Pension Plan are based on years of vested service at September 30, 2017, up to a maximum of thirty years, and the employee's average annual pay for the five highest consecutive years during the ten years preceding September 30, 2017, except for employees whose benefits were previously frozen during 2006. Pension Plan benefits are the present value of estimated future periodic payments that are attributable to services rendered by the employees to the valuation date. Benefits include the benefits expected to be paid to (a) retired or terminated employees or their beneficiaries and (b) present employees or their beneficiaries. The freeze of the Pension Plan effective September 30, 2017, required a remeasurement of the plan's projected benefit obligation. The combined impact of the remeasurement, an increase in fair value of underlying assets, the impact of the freeze and changes to participant's status as a result of the Corporation's restructuring efforts during the year ended December 31, 2017, resulted in an increase of the funded status of the Pension Plan. A discount rate of 3.68% was utilized to remeasure the projected benefit obligation as of December 31, 2017. There was less than $0.1 million of curtailment cost to the Corporation as a result of the amendment. The Pension Plan is fully funded as of December 31, 2017 . At December 31, 2017 , the Corporation had 100 employees who had accrued benefits under the Pension Plan, which contributions are intended to provide benefits attributable to service-to-date employees. Pension Plan expense was a benefit of $1.5 million in 2017 , compared to expenses of $0.1 million in 2016 and $1.6 million in 2015 . Nonqualified Pension Plan The Corporation has a supplemental defined benefit nonqualified pension plan, the Chemical Financial Corporation Supplemental Pension Plan ("SERP"). The Corporation established the SERP to provide payments to certain executive officers of the Corporation, as determined by the Compensation and Pension Committee. The Internal Revenue Code limits both the amount of eligible compensation for benefit calculation purposes and the amount of annual benefits that may be paid from a tax-qualified retirement plan. The SERP was designed to provide benefits to which executive officers of the Corporation would have been entitled, calculated under the provisions of the Pension Plan, as if the limits imposed by the Internal Revenue Code did not apply. The SERP is an unfunded plan and, therefore, has no assets. Effective September 30, 2017, the Pension and Compensation Committee approved a curtailment to the SERP, due to the retirement of the final remaining participant in the SERP. The curtailment, in addition to changes in valuation of liabilities, resulted in a reduction in obligation during the year ended December 31, 2017. As of December 31, 2017 , a $2.4 million liability included in other liabilities was recorded in the Consolidated Statements of Financial Position related to the SERP. As of December 31, 2017 , the SERP had no active participants. Nonqualified Postretirement Benefit Plan The Corporation has a nonqualified postretirement benefit plan ("Postretirement Plan") that provides medical and dental benefits, upon retirement, to a limited number of active and retired employees. The majority of the retirees are required to make contributions toward the cost of their benefits based on their years of credited service and age at retirement. Beginning January 1, 2012, the Corporation amended the Postretirement Plan to extend coverage to employees who were at least age 50 as of January 1, 2012. These employees must also retire at age 60 or older, have at least twenty-five years of service with the Corporation and be participating in the active employee group health insurance plan in order to be eligible to participate in the Corporation's Postretirement Plan. Eligible employees may also cover their spouse until age 65 as long as the spouse is not offered health insurance coverage through his or her employer. Employees and their spouses eligible to participate in the Postretirement Plan will be required to make contributions toward the cost of their benefits upon retirement, with the contribution levels designed to cover the projected overall cost of these benefits over the long-term. Retiree contributions are generally adjusted annually. The accounting for these postretirement benefits anticipates changes in future cost-sharing features such as retiree contributions, deductibles, copayments and coinsurance. The Corporation reserves the right to amend, modify or terminate these benefits at any time. 401(k) Savings Plan The Corporation's 401(k) Savings Plan provides an employer match, in addition to a 4.0% contribution for all employees, with the exception of employees participating the Pension Plan discussed above, during the time period they were eligible to earn service credits. The 401(k) Savings Plan is available to all regular employees and provides employees with tax deferred salary deductions and alternative investment options. The Corporation matches 50.0% of the participants' elective deferrals on the first 4.0% of the participants' base compensation up to the maximum amount allowed under the Internal Revenue Code. The 401(k) Savings Plan provides employees with the option to invest in the Corporation's common stock. The Corporation's match under the 401(k) Savings Plan was $2.9 million in 2017 , $3.0 million in 2016 and $1.6 million in 2015 . Employer contributions to the 401(k) Savings Plan for the 4.0% benefit for employees totaled $6.2 million in 2017 , $3.5 million in 2016 and $3.1 million in 2015 . The combined amount of the employer match and 4.0% contribution to the 401(k) Savings Plan totaled $9.1 million in 2017 , $6.5 million in 2016 and $4.7 million in 2015 . Multi-Employer Defined Benefit Plan In conjunction with the April 1, 2015 acquisition of Monarch, the Corporation acquired a participation in the Pentegra Defined Benefit Plan for Financial Institutions (Pentegra DB Plan), a qualified defined benefit plan. Employee benefits for Monarch employees under the Pentegra DB Plan were frozen effective April 1, 2004. The Pentegra DB Plan operates as a multi-employer plan for accounting purposes and as a multiple employer plan under the Employee Retirement Income Security Act of 1974 and the Internal Revenue Code (IRC). The Pentegra DB Plan is a single plan under IRC Section 413(c) and, as a result, all the plan's assets stand behind all of the plan's liabilities. Accordingly, contributions made by a participating employer may be used to provide benefits to participants of other participating employers. No contributions were made to the Pentegra DB Plan during the years ended December 31, 2017 and 2016 . The Pentegra DB Plan's Employer Identification Number is 13-5645888 and the Plan Number is 333. Financial information for the Pentegra DB Plan, which maintains a June 30 year end, is made available through the public Form 5500 which is available by April 15th of the year following the plan year end. The Pentegra DB Plan was fully funded as of its most recent year end. The Corporation's allocation of assets and liabilities in the Pentegra DB Plan totaled $3.7 million and $2.6 million respectively, as of December 31, 2017 , and the Corporation's allocation of assets comprised 0.1% of the plan's total assets at that date. Benefit Obligations and Plan Expenses The following schedule sets forth the changes in the projected benefit obligation and plan assets of the Corporation's Plans: Pension Plan Postretirement Plan SERP (Dollars in thousands) 2017 2016 2017 2016 2017 2016 Projected benefit obligation: Benefit obligation at beginning of year $ 123,968 $ 119,873 $ 2,601 $ 3,247 $ 2,567 $ 2,160 Service cost 639 1,041 5 9 61 77 Interest cost 4,966 5,335 94 132 69 92 Settlement and other charges (1) — — — — — (264 ) Net actuarial loss (gain) 10,131 2,684 10 (478 ) (274 ) 536 Benefits paid (6,432 ) (4,965 ) (198 ) (309 ) — (34 ) Curtailment (11,911 ) — — — — — Benefit obligation at end of year 121,361 123,968 2,512 2,601 2,423 2,567 Fair value of plan assets: Fair value of plan assets at beginning of year 132,751 126,930 — — — — Actual return on plan assets 19,582 10,786 — — — — Employer contributions — — 198 309 — — Benefits paid (6,432 ) (4,965 ) (198 ) (309 ) — — Fair value of plan assets at end of year 145,901 132,751 — — — — Funded (unfunded) status at December 31 $ 24,540 $ 8,783 $ (2,512 ) $ (2,601 ) $ (2,423 ) $ (2,567 ) Accumulated benefit obligation $ 121,361 $ 115,418 $ 2,512 $ 2,601 $ 2,423 $ 2,567 (1) The settlement and other charges relate to the change in control as a result of the merger with Talmer as of August 31, 2016. The Corporation did not make a contribution to the Pension Plan in either 2017 or 2016 . The Corporation is not required to make a contribution to the Pension Plan in 2018 . Weighted-average rate assumptions of the Corporation's Plans follow: Pension Plan Postretirement Plan SERP 2017 2016 2015 2017 2016 2015 2017 2016 2015 Discount rate used in determining benefit obligation — December 31 3.68 % 4.22 % 4.55 % 3.41 % 3.79 % 4.23 % 3.38 % 3.63 % 4.51 % Discount rate used in determining expense 4.22 4.55 4.15 3.79 4.23 3.75 — 4.51 4.07 Discount rate used in determining expense — prior to remeasurement 3.81 — — — — — 3.63 2.87 — Expected long-term return on Pension Plan assets 6.75 6.75 6.75 — — — — — — Rate of compensation increase used in determining benefit obligation — December 31 — 3.50 3.50 — — — — 3.50 3.50 Rate of compensation increase used in determining pension expense 3.50 3.50 3.50 — — — 3.50 3.50 3.50 Year 1 increase in cost of postretirement benefits — — — 6.5 7.0 7.5 — — — Net periodic pension cost (income) of the Corporation's Plans was as follows for the years ended December 31: Pension Plan Postretirement Plan SERP (Dollars in thousands) 2017 2016 2015 2017 2016 2015 2017 2016 2015 Service cost $ 639 $ 1,041 $ 1,021 $ 5 $ 9 $ 16 $ 61 $ 77 $ 70 Interest cost 4,966 5,335 5,242 94 132 133 69 92 85 Expected return on plan assets (8,938 ) (8,562 ) (8,645 ) — — — — — — Amortization of prior service credit — — (5 ) — 117 130 — — — Amortization of net actuarial loss (gain) 1,837 2,259 3,962 (162 ) (100 ) (1 ) 77 78 262 Curtailment 1 — — — — — — — — Settlement (1) — — — — — — 322 120 — Net cost (income) $ (1,495 ) $ 73 $ 1,575 $ (63 ) $ 158 $ 278 $ 529 $ 367 $ 417 (1) The settlement charge relates to the settlement of liabilities under the SERP for the retirement of the plan participant during the third quarter of 2017 and the change in control as a result of the merger with Talmer as of August 31, 2016. The following schedule presents estimated future benefit payments for the next 10 years under the Corporation's Plans for retirees already receiving benefits and future retirees, assuming they retire and begin receiving unreduced benefits as soon as they are eligible: (Dollars in thousands) Pension Plan Postretirement Plan SERP 2018 $ 6,001 $ 230 $ 2,063 2019 6,297 230 22 2020 6,392 231 22 2021 6,657 230 22 2022 6,787 227 22 2023 - 2027 35,689 973 107 Total $ 67,823 $ 2,121 $ 2,258 For measurement purposes for the Postretirement Plan, the annual rates of increase in the per capita cost of covered health care benefits and dental benefits for 2018 were each assumed at 7.5% . These rates were assumed to decrease gradually to 5.0% in 2020 and remain at that level thereafter. The assumed health care and dental cost trend rates could have a significant effect on the amounts reported for the Postretirement Plan. A one percentage-point change in these rates would have the following effects: One Percentage-Point (Dollars in thousands) Increase Decrease Effect on total of service and interest cost components in 2016 $ 8 $ (8 ) Effect on postretirement benefit obligation as of December 31, 2016 196 (177 ) Pension Plan Assets The assets of the Pension Plan are invested by the Wealth Management department of Chemical Bank. The investment policy and allocation of the assets of the pension trust were approved by the Compensation and Pension Committee of the board of directors of the Corporation. The Pension Plan's primary investment objective is long-term growth coupled with income. In consideration of the Pension Plan's fiduciary responsibilities, emphasis is placed on quality investments with sufficient liquidity to meet benefit payments and plan expenses, as well as providing the flexibility to manage the investments to accommodate current economic and financial market conditions. To meet the Pension Plan's long-term objective within the constraints of prudent management, target ranges have been set for the three primary asset classes: an equity securities range from 40.0% to 70.0% , a debt securities range from 20.0% to 60.0% , and a cash and cash equivalents and other range from 0.0% to 10.0% . Modest asset positions outside of these targeted ranges may occur due to the repositioning of assets within industries or other activity in the financial markets. Equity securities are primarily comprised of both individual securities and equity-based mutual funds, invested in either domestic or international markets. The stocks are diversified among the major economic sectors of the market and are selected based on balance sheet strength, expected earnings growth, the management team and position within their industries, among other characteristics. Debt securities are comprised of U.S. dollar denominated bonds issued by the U.S. Treasury, U.S. government agencies and investment grade bonds issued by corporations. The notes and bonds purchased are primarily rated "A" or better by the major bond rating companies from diverse industries. The Pension Plan's asset allocation by asset category was as follows: December 31, Asset Category 2017 2016 Equity securities 68 % 69 % Debt securities 28 29 Other 4 2 Total 100 % 100 % The following schedule sets forth the fair value of the Pension Plan's assets and the level of the valuation inputs used to value those assets at December 31, 2017 and 2016 : (Dollars in thousands) Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total December 31, 2017 Cash $ 5,238 $ — $ — $ 5,238 Equity securities: U.S. large- and mid-cap stocks (1) 68,909 — — 68,909 U.S. small-cap mutual funds 5,377 — — 5,377 International large-cap mutual funds 18,341 — — 18,341 Emerging markets mutual funds 7,363 — — 7,363 Debt securities: U.S. Treasury and government sponsored agency bonds and notes — 548 — 548 Mutual funds (3) 40,046 — — 40,046 Other 79 — — 79 Total $ 145,353 $ 548 $ — $ 145,901 December 31, 2016 Cash $ 2,825 $ — $ — $ 2,825 Equity securities: U.S. large- and mid-cap stocks (1) 55,389 — — 55,389 U.S. small-cap mutual funds 5,687 — — 5,687 International large-cap mutual funds 13,701 — — 13,701 Emerging markets mutual funds 5,147 — — 5,147 Chemical Financial Corporation common stock 11,412 — — 11,412 Debt securities: U.S. Treasury and government sponsored agency bonds and notes — 806 — 806 Corporate bonds (2) — 1,503 — 1,503 Mutual funds (3) 36,220 — — 36,220 Other 61 — — 61 Total $ 130,442 $ 2,309 $ — $ 132,751 (1) Comprised of common stocks and mutual funds traded on U.S. Exchanges whose issuers had market capitalizations exceeding $3 billion . (2) Comprised of investment grade bonds of U.S. issuers from diverse industries. (3) Comprised primarily of fixed-income bonds issued by the U.S. Treasury and government sponsored agencies and bonds of U.S. and foreign issuers from diverse industries. At December 31, 2017 and 2016 , equity securities included zero and 210,663 shares, respectively, of the Corporation's common stock. During both 2017 and 2016 , cash dividends of $0.2 million were paid on the Corporation's common stock held by the Pension Plan. The fair value of the Corporation's common stock held in the Pension Plan was zero at December 31, 2017 and $11.4 million at December 31, 2016 , which represented zero and 8.6% of Pension Plan assets at December 31, 2017 and 2016 , respectively. Accumulated Other Comprehensive Loss The following sets forth the changes in accumulated other comprehensive income (loss), net of tax, related to the Corporation's Pension Plan, Postretirement Plan and SERP during 2017 : (Dollars in thousands) Pension Plan Postretirement Plan SERP Total Accumulated other comprehensive income (loss) at beginning of year $ (26,123 ) $ 724 $ (495 ) $ (25,894 ) Comprehensive income (loss) adjustment: Prior service costs (credits) — — — — Net actuarial (income) loss 1,528 (112 ) 229 1,645 Curtailment 7,742 — — 7,742 Settlement (1) — — 209 209 Comprehensive income (loss) adjustment 9,270 (112 ) 438 9,596 Reclassification of certain income tax effects (2) (3,630 ) 132 (12 ) (3,510 ) Accumulated other comprehensive income (loss) at end of year $ (20,483 ) $ 744 $ (69 ) $ (19,808 ) (1) The settlement charge relates to the settlement of liabilities under the SERP for the retirement of the plan participant during the third quarter of 2017. (2) The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, see Note 1 for further information. The estimated income (loss) that will be amortized from accumulated other comprehensive income (loss) into net periodic cost, net of tax, in 2018 is as follows: (Dollars in thousands) Pension Plan Postretirement Plan SERP Total Prior service (costs) credits $ — $ — $ — $ — Net gain (loss) (561 ) 113 — (448 ) Total $ (561 ) $ 113 $ — $ (448 )

Equity

Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Equity	Equity Common Stock Repurchase Programs From time to time, the board of directors of the Corporation approves common stock repurchase programs allowing management to repurchase shares of the Corporation's common stock in the open market. The repurchased shares are available for later reissuance in connection with potential future stock dividends, the Corporation's dividend reinvestment plan, employee benefit plans and other general corporate purposes. Under these programs, the timing and actual number of shares subject to repurchase are at the discretion of management and are contingent on a number of factors, including the projected parent company cash flow requirements and the Corporation's market price per share. In January 2008, the board of directors of the Corporation authorized the repurchase of up to 500,000 shares of the Corporation's common stock under a stock repurchase program. In November 2011, the board of directors of the Corporation reaffirmed the stock buy-back authorization with the qualification that the shares may only be repurchased if the share price is below the tangible book value per share of the Corporation's common stock at the time of the repurchase. Since the January 2008 authorization, no shares have been repurchased. At December 31, 2017 , there were 500,000 remaining shares available for repurchase under the Corporation's stock repurchase programs. Shelf Registration On May 10, 2017, the Corporation filed an automatic shelf registration statement on Form S-3ASR with the SEC for an indeterminate amount of securities, which became immediately effective. The shelf registration statement provides the Corporation with the ability to raise capital, subject to SEC rules and limitations, if the board of directors of the Corporation decides to do so. Preferred Stock On April 20, 2015, the shareholders of the Corporation approved an amendment to the restated articles of incorporation which eliminated and replaced the previous class of 200,000 shares of preferred stock, approved by shareholders on April 20, 2009, with a new class of 2,000,000 shares of preferred stock. As of December 31, 2017 , no shares of preferred stock were issued and outstanding. Common Stock On July 19, 2016, the shareholders of the Corporation approved an amendment to the restated articles of incorporation to increase the number of authorized shares of common stock from 60,000,000 to 100,000,000 in anticipation of the merger with Talmer. On April 26, 2017, the shareholders of the Corporation approved an amendment to the restated articles of incorporation to increase the number of authorized shares of common stock from 100,000,000 to 135,000,000 .

Regulatory Capital and Reserve

Regulatory Capital and Reserve Requirements	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Regulatory Capital and Reserve Requirements	Regulatory Capital and Reserve Requirements Federal and state banking regulations place certain restrictions on the transfer of assets, in the form of dividends, loans, or advances, from Chemical Bank to the Corporation. As of December 31, 2017 , substantially all of the assets of Chemical Bank were restricted from transfer to the Corporation in the form of loans or advances. Dividends from the bank are the principal source of funds for the Corporation. In addition to the statutory limits, the Corporation considers the overall financial and capital position of the bank prior to making any cash dividend decisions. Banking regulations require that banks maintain cash reserve balances in vault cash, with the Federal Reserve Bank, or with certain other qualifying banks. The aggregate average amount of the regulatory balances required to be maintained by Chemical Bank during 2017 and 2016 were $71.7 million and $52.3 million , respectively. During 2017 , Chemical Bank satisfied its regulatory reserve requirements by maintaining a combination of vault cash balances and cash held with the FRB in excess of regulatory reserve requirements. Chemical Bank was not required to maintain compensating balances with correspondent banks during 2017 or 2016 . The Corporation and Chemical Bank are subject to various regulatory capital requirements administered by federal banking agencies. Under these capital requirements, Chemical Bank must meet specific capital guidelines that involve quantitative measures of assets and certain off-balance sheet items as calculated under regulatory accounting practices. In addition, capital amounts and classifications are subject to qualitative judgments by regulators. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Consolidated Financial Statements. Management believes as of December 31, 2017 , the Corporation and Chemical Bank met all capital adequacy requirements to which they are subject. Quantitative measures established by regulation to ensure capital adequacy require minimum ratios of Tier 1 capital to average assets (Leverage Ratio) and Common Equity Tier 1, Tier 1 and Total capital to risk-weighted assets. These capital guidelines assign risk weights to on- and off- balance sheet items in arriving at total risk-weighted assets. Minimum capital levels are based upon the perceived risk of various asset categories and certain off-balance sheet instruments. Risk-weighted assets for the Corporation and Chemical Bank totaled $14.74 billion and $14.70 billion , respectively, at December 31, 2017 , compared to $13.42 billion and $13.36 billion at December 31, 2016 , respectively. Effective January 1, 2015, the Corporation adopted the Basel III regulatory capital framework as approved by federal banking agencies, which is subject to a multi-year phase-in period. The adoption of this new framework modified the calculation of the various capital ratios, added a new ratio, common equity tier 1, and revised the adequately and well capitalized thresholds. In addition, Basel III establishes a new capital conservation buffer of 2.5% of risk-weighted assets, which is phased-in over a four-year period beginning January 1, 2016. The capital conservation buffer for 2017 is 1.25% and was 0.625% for 2016. The Corporation has elected to opt-out of including accumulated other comprehensive income in common equity tier 1 capital. At December 31, 2017 and 2016 , Chemical Bank's capital ratios exceeded the quantitative capital ratios required for an institution to be considered "well-capitalized." Significant factors that may affect capital adequacy include, but are not limited to, a disproportionate growth in assets versus capital and a change in mix or credit quality of assets. There are no conditions or events since that notification that management believes have changed the institutions' category. The summary below compares the actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy: Actual Minimum Required for Capital Adequacy Purposes Minimum Required for Capital Adequacy Purposes Plus Capital Conservation Buffer Required to be Well Capitalized Under Prompt Corrective Action Regulations (Dollars in thousands) Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio December 31, 2017 Total Capital to Risk-Weighted Assets Corporation $ 1,614,046 11.0 % $ 1,179,076 8.0 % $ 1,363,307 9.3 % N/A N/A Chemical Bank 1,613,087 11.0 1,176,361 8.0 1,360,167 9.3 $ 1,470,451 10.0 % Tier 1 Capital to Risk-Weighted Assets Corporation 1,498,463 10.2 884,307 6.0 1,068,538 7.3 N/A N/A Chemical Bank 1,513,219 10.3 882,271 6.0 1,066,077 7.3 1,176,361 8.0 Common Equity Tier 1 Capital to Risk-Weighted Assets Corporation 1,498,463 10.2 663,230 4.5 847,461 5.8 N/A N/A Chemical Bank 1,513,219 10.3 661,703 4.5 845,509 5.8 955,793 6.5 Leverage Ratio Corporation 1,498,463 8.3 720,890 4.0 720,890 4.0 N/A N/A Chemical Bank 1,513,219 8.4 720,043 4.0 720,043 4.0 900,053 5.0 December 31, 2016 Total Capital to Risk-Weighted Assets Corporation $ 1,543,018 11.5 % $ 1,073,431 8.0 % $ 1,157,293 8.6 % N/A N/A Chemical Bank 1,608,980 12.0 1,068,560 8.0 $ 1,152,041 8.6 $ 1,335,700 10.0 % Tier 1 Capital to Risk-Weighted Assets Corporation 1,441,209 10.7 805,073 6.0 888,935 6.6 N/A N/A Chemical Bank 1,522,711 11.4 801,420 6.0 884,901 6.6 1,068,560 8.0 Common Equity Tier 1 Capital to Risk-Weighted Assets Corporation 1,441,209 10.7 603,805 4.5 687,667 5.1 N/A N/A Chemical Bank 1,522,711 11.4 601,065 4.5 684,546 5.1 868,205 6.5 Leverage Ratio Corporation 1,441,209 9.0 643,603 4.0 643,603 4.0 N/A N/A Chemical Bank 1,522,711 9.5 641,457 4.0 641,457 4.0 801,822 5.0 During the years ended December 31, 2017 , 2016 and 2015 , Chemical Bank paid dividends to the Corporation totaling $165.0 million , $110.5 million and $56.9 million , respectively. On January 23, 2018 , a cash dividend on the Corporation's common stock of $0.28 per share was declared. The dividend will be paid on March 16, 2018 to shareholders of record as of March 2, 2018 .

Parent Company Only Financial S

Parent Company Only Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Parent Company Only Financial Statements	Parent Company Only Financial Statements Condensed financial statements of Chemical Financial Corporation (parent company) only follow: Condensed Statements of Financial Position December 31, (Dollars in thousands) 2017 2016 Assets Cash at subsidiary bank $ 5,761 $ 16,851 Investment in subsidiaries 2,673,858 2,654,458 Premises and equipment 3,931 4,051 Goodwill 1,092 1,092 Deferred tax asset 7,203 30,715 Other assets 31,459 32,869 Total assets $ 2,723,304 $ 2,740,036 Liabilities Other liabilities $ 18,877 $ 18,345 Non-revolving line-of-credit 19,963 124,625 Subordinated debentures 15,715 15,540 Total liabilities 54,555 158,510 Shareholders' equity 2,668,749 2,581,526 Total liabilities and shareholders' equity $ 2,723,304 $ 2,740,036 Condensed Statements of Income Years Ended December 31, (Dollars in thousands) 2017 2016 2015 Income Cash dividends from subsidiaries $ 165,000 $ 110,450 $ 56,860 Other income 921 151 144 Total income 165,921 110,601 57,004 Expenses Interest expense 3,076 1,816 761 Operating expenses 23,298 30,589 7,794 Total expenses 26,374 32,405 8,555 Income before income taxes and equity in undistributed net income of subsidiaries 139,547 78,196 48,449 Income tax benefit 12,670 11,378 2,582 Equity in undistributed net (loss) income of subsidiaries (2,694 ) 18,458 35,799 Net income $ 149,523 $ 108,032 $ 86,830 Condensed Statements of Cash Flows Years Ended December 31, (Dollars in thousands) 2017 2016 2015 Cash Flows From Operating Activities Net income $ 149,523 $ 108,032 $ 86,830 Adjustments to reconcile net income to net cash provided by operating activities: Share-based compensation expense 17,346 13,452 3,478 Depreciation of premises and equipment 408 355 318 Equity in undistributed net loss (income) of subsidiaries 2,694 (18,458 ) (35,799 ) Net decrease in other assets 1,410 9,752 2,873 Net increase (decrease) in other liabilities 25,178 (11,830 ) (19,033 ) Net cash provided by operating activities 196,559 101,303 38,667 Cash Flows From Investing Activities Cash paid, net of cash assumed, in business combinations — (107,622 ) (45,267 ) Purchases of premises and equipment, net (288 ) (774 ) (320 ) Net cash used in investing activities (288 ) (108,396 ) (45,587 ) Cash Flows From Financing Activities Cash dividends paid (78,498 ) (49,389 ) (36,918 ) Proceeds from issuance of common stock, net of issuance costs — — — Repayment of subordinated debt obligations — (18,558 ) — Repayments of other borrowings (105,000 ) (62,500 ) — Proceeds from issuance of other borrowings — 125,000 25,000 Proceeds from directors' stock purchase plan and exercise of stock options 3,991 1,572 2,473 Cash paid for payroll taxes upon conversion of restricted stock units (27,854 ) (1,065 ) (571 ) Net cash used in financing activities (207,361 ) (4,940 ) (10,016 ) Net decrease in cash and cash equivalents (11,090 ) (12,033 ) (16,936 ) Cash and cash equivalents at beginning of year 16,851 28,884 45,820 Cash and cash equivalents at end of year $ 5,761 $ 16,851 $ 28,884 Business combinations: Fair value of assets acquired (noncash) $ — $ 46,898 $ 10,304 Liabilities assumed — 58,309 42,019 Common stock and stock options issued — 1,504,811 159,904

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share The two-class method is used in the calculation of basic and diluted earnings per share. Under the two-class method, earnings available to common shareholders for the period are allocated between common shareholders and participating securities according to dividends declared (or accumulated) and participating rights in undistributed earnings. Average shares of common stock for diluted net income per common share include shares to be issued upon the exercise of stock options granted under the Corporation’s share-based compensation plans, restricted stock units that may be converted to stock, restricted stock awards and stock to be issued under the deferred stock compensation plan for non-employee directors. The factors used in the earnings per share computation follow: For the years ended December 31, (In thousands, except per share data) 2017 2016 2015 Net income $ 149,523 $ 108,032 $ 86,830 Net income allocated to participating securities 495 166 — Net income allocated to common shareholders (1) $ 149,028 $ 107,866 $ 86,830 Weighted average common shares - issued 71,103 49,091 36,081 Average unvested restricted share awards (238 ) (139 ) — Weighted average common shares outstanding - basic 70,865 48,952 36,081 Effect of dilutive securities Weighted average common stock equivalents 648 651 272 Weighted average common shares outstanding - diluted 71,513 49,603 36,353 EPS available to common shareholders Basic earnings per common share $ 2.11 $ 2.21 $ 2.41 Diluted earnings per common share $ 2.08 $ 2.17 $ 2.39 (1) Net income allocated to common shareholders for basic and diluted earnings per share may differ under the two-class method as a result of adding common share equivalents for options and warrants to dilutive shares outstanding, which alters the ratio used to allocate net income to common shareholders and participating securities for the purposes of calculating diluted earnings per share. For the effect of dilutive securities, the assumed average stock valuation is $50.26 per share, $40.58 per share and $32.17 per share for the years ended December 31, 2017 , 2016 and 2015 , respectively. The average number of exercisable employee stock option awards outstanding that were "out-of-the-money," whereby the option exercise price per share exceeded the market price per share and, therefore, were not included in the computation of diluted earnings per common share because they would have been anti-dilutive, totaled 107,272 for the year ended December 31, 2017 , 0 for the year ended December 31, 2016 and 54,771 for the year ended December 31, 2015 .

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss The following table summarizes the changes within each component of accumulated other comprehensive income (loss), net of related tax benefit/expense for the years ended December 31, 2017 , 2016 and 2015 : (Dollars in thousands) Unrealized gains Defined Benefit Pension Plans Unrealized gains (losses) on cash flow hedges, net of tax Total For the year ended December 31, 2017 Beginning balance $ (14,142 ) $ (25,894 ) $ — $ (40,036 ) Other comprehensive loss before reclassifications 826 8,457 2,771 12,054 Amounts reclassified from accumulated other comprehensive income 4,802 1,139 1,061 7,002 Net current period other comprehensive income (loss) 5,628 9,596 3,832 19,056 Reclassification of certain deferred tax effects (1) (1,834 ) (3,510 ) 826 (4,518 ) Ending balance $ (10,348 ) $ (19,808 ) $ 4,658 $ (25,498 ) For the year ended December 31, 2016 Beginning balance $ (1,888 ) $ (27,144 ) $ — $ (29,032 ) Other comprehensive income (loss) before reclassifications (12,170 ) (229 ) — (12,399 ) Amounts reclassified from accumulated other comprehensive income (84 ) 1,479 — 1,395 Net current period other comprehensive income (loss) (12,254 ) 1,250 — (11,004 ) Ending balance $ (14,142 ) $ (25,894 ) $ — $ (40,036 ) For the year ended December 31, 2015 Beginning balance $ (210 ) $ (32,243 ) $ — $ (32,453 ) Other comprehensive income (loss) before reclassifications (1,269 ) 2,443 — 1,174 Amounts reclassified from accumulated other comprehensive income (409 ) 2,656 — 2,247 Net current period other comprehensive income (loss) (1,678 ) 5,099 — 3,421 Ending balance $ (1,888 ) $ (27,144 ) $ — $ (29,032 ) (1) The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, see Note 1 for further information. The following table summarizes the amounts reclassified out of each component of accumulated other comprehensive income (loss) for the years ended December 31, 2017, 2016 and 2015: (Dollars in thousands) Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Income Statement December 31, 2017 December 31, 2016 December 31, 2015 Gains and losses on available-for-sale securities $ (7,388 ) $ 129 $ 630 Net gain on sale of investment securities (noninterest income) 2,586 (45 ) (221 ) Income tax (expense)/benefit $ (4,802 ) $ 84 $ 409 Net Income Amortization of defined benefit pension plan items $ (1,752 ) $ (2,276 ) $ (4,086 ) Salaries, wages and employee benefits (operating expenses) 613 797 1,430 Income tax (expense)/benefit $ (1,139 ) $ (1,479 ) $ (2,656 ) Net Income Gains and losses on cash flow hedges 1,633 — — Interest on short-term borrowings (interest expense) (572 ) — — Income tax (expense)/benefit $ 1,061 $ — $ — Net Income (loss)

Summary of Quarterly Statements

Summary of Quarterly Statements of Income (Unaudited)	12 Months Ended
	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Summary of Quarterly Statements of Income (Unaudited)	Summary of Quarterly Statements of Income (Unaudited) The following is a summary of the unaudited quarterly results of operation for the years ended December 31, 2017 , 2016 and 2015 . In the opinion of management, the information reflects all adjustments that are necessary for the fair presentation of the results of operations for the periods presented. 2017 (Dollars in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Total Interest income $ 142,896 $ 155,133 $ 164,944 $ 169,162 $ 632,135 Interest expense 12,799 17,185 21,316 23,257 74,557 Net interest income 130,097 137,948 143,628 145,905 557,578 Provision for loan losses 4,050 6,229 5,499 7,522 23,300 Noninterest income 38,010 41,568 32,122 32,319 144,019 Operating expenses 104,196 98,237 119,539 100,022 421,994 Income before income taxes 59,861 75,050 50,712 70,680 256,303 Income tax expense 12,257 23,036 10,253 61,234 106,780 Net income $ 47,604 $ 52,014 $ 40,459 $ 9,446 $ 149,523 Net income per common share: Basic $ 0.67 $ 0.73 $ 0.57 $ 0.13 $ 2.11 Diluted 0.67 0.73 0.56 0.13 2.08 Cash dividends declared per common share 0.27 0.27 0.28 0.27 1.10 2016 (Dollars in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Total Interest income $ 79,464 $ 82,937 $ 103,562 $ 144,416 $ 410,379 Interest expense 5,134 5,442 6,753 11,969 29,298 Net interest income 74,330 77,495 96,809 132,447 381,081 Provision for loan losses 1,500 3,000 4,103 6,272 14,875 Noninterest income 19,419 20,897 27,770 54,264 122,350 Operating expenses 58,887 59,085 106,144 114,302 338,418 Income before income taxes 33,362 36,307 14,332 66,137 150,138 Income tax expense 9,757 10,532 2,848 18,969 42,106 Net income $ 23,605 $ 25,775 $ 11,484 $ 47,168 $ 108,032 Net income per common share: Basic $ 0.61 $ 0.67 $ 0.23 $ 0.67 $ 2.21 Diluted 0.60 0.67 0.23 0.66 2.17 Cash dividends declared per common share 0.26 0.26 0.27 0.27 1.06 2015 (Dollars in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Total Interest income $ 62,630 $ 69,679 $ 78,851 $ 80,629 $ 291,789 Interest expense 3,450 3,944 5,234 5,153 17,781 Net interest income 59,180 65,735 73,617 75,476 274,008 Provision for loan losses 1,500 1,500 1,500 2,000 6,500 Noninterest income 19,275 20,674 20,215 20,052 80,216 Operating expenses 51,020 56,785 58,265 57,824 223,894 Income before income taxes 25,935 28,124 34,067 35,704 123,830 Income tax expense 8,100 9,100 9,600 10,200 37,000 Net income $ 17,835 $ 19,024 $ 24,467 $ 25,504 $ 86,830 Net income per common share: Basic $ 0.54 $ 0.54 $ 0.64 $ 0.67 $ 2.41 Diluted 0.54 0.54 0.64 0.66 2.39 Cash dividends declared per common share 0.24 0.24 0.26 0.26 1.00

Summary of Significant Accoun33

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations Chemical Financial Corporation ("Corporation" or "Chemical") operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within Michigan, Northeast Ohio and Northern Indiana as a Michigan state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of seven regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the Corporation's geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation's regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is generally uniform throughout the Corporation's regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products. The Corporation's primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts, wealth management revenue, net gain on sale of loans and other mortgage banking revenue.
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accounting and reporting policies of the Corporation and its subsidiaries have been prepared in accordance with U.S. Generally Accepted Accounting Principles ("GAAP"), Securities and Exchange Commission ("SEC") rules and interpretive releases and prevailing practices within the banking industry. The Consolidated Financial Statements of the Corporation include the accounts of the Corporation and its wholly owned subsidiaries. All significant income and expenses are recorded on the accrual basis. Intercompany accounts and transactions have been eliminated in preparing the Consolidated Financial Statements.
Use of Estimates	Use of Estimates Management makes estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, income and other taxes the valuation of loan servicing rights. Actual results could differ from these estimates.
Business Combinations	Business Combinations Pursuant to the guidance of the Financial Accounting Standards Board's ("FASB") Accounting Standards Codification ("ASC") Topic 805, Business Combinations ("ASC 805"), the Corporation recognizes assets acquired, including identified intangible assets, and the liabilities assumed in acquisitions at their fair values as of the acquisition date, with the acquisition-related transaction and restructuring costs expensed in the period incurred. See Note 2 for further information regarding the Corporation's mergers and acquisitions.
Cash and Cash Equivalents	Cash and Cash Equivalents For purposes of reporting cash flows, cash and cash equivalents include cash on hand and interest-bearing deposits held at the Federal Reserve Bank ("FRB").
Investment Securities	Investment Securities Investment securities include investments in debt, trust preferred and preferred stock securities. Investment securities are accounted for in accordance with ASC Topic 320, Investments — Debt and Equity Securities ("ASC 320"), which requires investments to be classified within one of three categories (trading, held-to-maturity or available-for-sale). The Corporation held no trading investment securities at December 31, 2017 or 2016 . Designation as an investment security held-to-maturity is based on the Corporation's intent and ability to hold the security to maturity. Investment securities held-to-maturity are carried at amortized cost, adjusted for purchase price premiums and accretion of discounts. Investment securities that are not held-to-maturity are accounted for as securities available-for-sale, and are stated at estimated fair value, with the aggregate unrealized gains and losses classified as a component of accumulated other comprehensive income (loss), net of income taxes. Realized gains and losses on the sale of investment securities charges are determined using the specific identification method and are included within noninterest income in the Consolidated Statements of Income. Premiums and discounts on investment securities are amortized over the estimated lives of the related investment securities based on the effective interest yield method and are included in interest income in the Consolidated Statements of Income. The Corporation assesses equity and debt securities that have fair values below amortized cost basis to determine whether declines (impairment) are other-than-temporary. If the Corporation intends to sell an impaired security or it is more-likely-than-not that the Corporation will be required to sell an impaired security prior to the recovery of its amortized cost, an other-than-temporary impairment ("OTTI") write-down is recognized in earnings equal to the entire difference between the investment security's amortized cost basis and its fair value. In assessing whether OTTI exists, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, (iii) the potential for impairments in an entire industry or sub-sector and (iv) the potential for impairments in certain economically depressed geographical locations.
Nonmarketable Equity Securities	Nonmarketable Equity Securities The Corporation is required to hold non-marketable equity securities, comprised of Federal Home Loan Bank of Indianapolis ("FHLB") and FRB stock, as a condition of membership. These securities are accounted for at cost, which equals par or redemption value, and included in "interest receivable and other assets" on the Consolidated Statements of Financial Position. These securities do not have a readily determinable fair value as their ownership is restricted and there is no market for these securities. These securities can only be redeemed or sold at their par value and only to the respective issuing government supported institution or to another member institution. FHLB stock can only be redeemed upon giving a five year written notice and FRB stock can only be redeemed upon giving six months written notice, with no more than 25.0% eligible for redemption in any calendar year. The Corporation records these non-marketable equity securities as a component of other assets and they are periodically evaluated for impairment. Management considers these non-marketable equity securities to be long-term investments. Accordingly, when evaluating these securities for impairment, management considers the ultimate recoverability of the par value rather than recognizing temporary declines in value, if applicable. The estimated loss is recognized as a loss from equity investments in other noninterest income in the Consolidated Statements of Income. The Corporation's ownership of FHLB stock totaled $112.0 million at December 31, 2017 and $58.0 million at December 31, 2016 . The Corporation's ownership of FRB stock totaled $68.1 million at December 31, 2017 and $39.4 million at December 31, 2016 .
Loans Held for Sale	Loans Held for Sale Mortgage and construction loans intended for sale in the secondary market are carried at fair value based on the Corporation's election of the fair value option. The estimated fair value of loans held for sale are based on quoted market prices for securities backed by similar types of loans, where available, or by discounting estimated cash flows using observable inputs inclusive of interest rates, prepayment speeds and loss assumptions for similar collateral. The fair value includes the servicing value of the loans as well as any accrued interest. These loans are sold both with servicing rights retained and with servicing rights released.
Originated Loans Held for Investment	Originated Loans Held for Investment Originated loans include the Corporation's entire portfolio loans held for investment, excluding loans acquired in business combinations, as further discussed below. Originated loans are stated at their principal amount outstanding, net of unearned income, charge-offs and unamortized deferred fees and costs. Loan interest income is recognized on the accrual basis. Deferred loan fees and costs are amortized over the loan term based on the level-yield method. Net loan commitment fees are deferred and amortized into fee income on a straight-line basis over the commitment period. If a loan is transferred from the loan held for investment portfolio to the held for sale portfolio, any write-down in the carrying amount of the loan at the date of transfer is recorded as a charge-off. The loans are transferred at fair value determined using the same methods described above for held for sale loans. When loans classified as held for investment are transferred to loans held for sale due to a change in intent, cash flows associated with the loans will be classified in the Consolidated Statements of Cash Flows as operating or investing, as appropriate, in accordance with the initial classification of the loans. The past due status of a loan is based on the loan's contractual terms. A loan is placed in nonaccrual status (accrual of interest is discontinued) when principal or interest is past due 90 days or when doubt exists as to the ultimate collection of principal or interest, unless the loan is both well-secured and in the process of collection, or earlier when, in the opinion of management, there is sufficient reason to doubt the collectibility of principal or interest. Interest previously accrued, but not collected, is reversed and charged against interest income at the time the loan is placed in nonaccrual status. Subsequent receipts of interest while a loan is in nonaccrual status are recorded as a reduction of principal. Loans are returned to accrual status when principal and interest payments are brought current and are anticipated to be fully collectible, payments have been received consistently for a period of time (generally six months) and collectibility is no longer in doubt.
Loans Acquired in a Business Combination	Loans Acquired in a Business Combination Loans acquired in a business combination ("acquired loans") consist of loans acquired on August 31, 2016 in the merger with Talmer, on May 31, 2015 in the acquisition of Lake Michigan Financial Corporation ("Lake Michigan"), on April 1, 2015 in the acquisition of Monarch Community Bancorp, Inc. ("Monarch"), on October 31, 2014 in the acquisition of Northwestern Bancorp, Inc. ("Northwestern"), and on April 30, 2010 in the acquisition of O.A.K. Financial Corporation ("OAK"). Acquired loans were recorded at fair value at the date of acquisition, without a carryover of the associated allowance for loan losses related to these loans. The Corporation accounts for acquired loans, which are recorded at fair value at acquisition using an estimate of cash flows deemed to be collectible and an accretable yield, in accordance with ASC Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality ("ASC 310-30"). ASC 310-30 allows investors to aggregate loans acquired into loan pools that have common risk characteristics and thereby use a composite interest rate and expectation of cash flows expected to be collected for the loan pools. Under the provisions of ASC 310-30, the Corporation aggregated acquired loans into pools within each merger or acquisition based upon common risk characteristics, including types of loans, commercial type loans with similar risk grades and whether loans were performing or nonperforming. A pool is considered a single unit of accounting for the purposes of applying the guidance prescribed in ASC 310-30. A loan will be removed from a pool of acquired loans only if the loan is sold, foreclosed, paid off or written off, and will be removed from the pool at the carrying value. The estimate of expected credit losses was determined based on due diligence performed by executive and senior officers of the Corporation, with assistance from third-party consultants. The Corporation estimated the cash flows expected to be collected over the life of the pools of loans at acquisition and estimates expected cash flows quarterly thereafter, based on a set of assumptions including expectations as to default rates, prepayment rates and loss severities. The Corporation must make numerous assumptions, interpretations and judgments using internal and third-party credit quality information to determine whether it is probable that the Corporation will be able to collect all contractually required payments. This is a point in time assessment and inherently subjective due to the nature of the available information and judgment involved. The calculation of the fair value of the acquired loan pools entails estimating the amount and timing of cash flows attributable to both principal and interest expected to be collected on such loan pools and then discounting those cash flows at market interest rates. The excess of a loan pool's expected cash flows at the acquisition date over its estimated fair value is referred to as the "accretable yield," which is recognized into interest income over the estimated remaining life of the loan pool on a level-yield basis. The difference between a loan pool's contractually required principal and interest payments at the acquisition date and the cash flows expected to be collected at the acquisition date is referred to as the "nonaccretable difference," which includes an estimate of future credit losses expected to be incurred over the estimated life of the loan pool and interest payments that are not expected to be collected. Decreases to the expected cash flows in each loan pool in subsequent periods will require the Corporation to record a provision for loan losses and establish an allowance for loan loss. Improvements in expected cash flows in each loan pool in subsequent periods will result in reversing a portion of the nonaccretable difference, which is then classified as part of the accretable yield and subsequently recognized into interest income over the estimated remaining life of the loan pool.
Loans Modified Under Troubled Debt Restructurings	Loans Modified Under Troubled Debt Restructurings Loans modified under TDRs involve granting a concession to a borrower who is experiencing financial difficulty. Concessions generally include modifications to original loan terms, including changes to a loan's payment schedule, principal forgiveness, interest rate reductions, or other actions intended to minimize our economic loss and to avoid foreclosure or repossession of the collateral, if applicable, which generally would not otherwise be considered. The Corporation's TDRs include accruing TDRs, which consist of originated loans that continue to accrue interest as the Corporation expects to collect the remaining principal and interest on the loan, and nonaccrual TDRs, which include originated loans that are in a nonaccrual status and are no longer accruing interest, as the Corporation does not expect to collect the full amount of principal and interest owed from the borrower on these loans. All TDRs are accounted for as impaired loans and are included in the Corporation's analysis of the allowance for loan losses. A TDR that has been renewed by a borrower who is no longer experiencing financial difficulty and which yields a market rate of interest at the time of a renewal is no longer reported as a TDR, but only if they have been refinanced or restructured at market terms and qualify as a new loan. Loans in the Corporation's commercial loan portfolio (comprised of commercial, commercial real estate, real estate construction and land development loans) that meet the definition of a TDR generally consist of loans where the Corporation has allowed borrowers to defer scheduled principal payments and make interest-only payments for a specified period of time at the stated interest rate of the original loan agreement or reduced payments due to a moderate extension of the loan's contractual term. If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR and impairment is measured based on collateral values, if the loan is collateral dependent. If the Corporation does not expect to incur a loss on the loan based on its assessment of the borrowers' expected cash flows, as the pre- and post-modification effective yields are approximately the same, the loan is current and a six-month payment history has been sustained, the loan is classified as an accruing TDR. Since no loss is expected to be incurred on these loans, no additional provision for loan losses has been recognized for these loans and they continue to accrue interest at their contractual interest rate. Accruing TDRs are transferred to nonaccrual status if they become 90 days past due as to principal or interest payments or if it is probable that any remaining principal and interest payments due on the loan will not be collected in accordance with the modified terms of the loan. If accruing TDRs are deemed to be collateral dependent, they are measured based on collateral values. Loans in the Corporation's consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a TDR include a concession that reduces a borrower's monthly payments by decreasing the interest rate charged on the loan for a specified period of time (generally 24 months) under a formal modification agreement. The Corporation recognizes an additional provision for loan losses related to impairment on these loans on an individual basis based on the present value of expected future cash flows discounted at the loan's original effective interest rate. These loans continue to accrue interest at their effective interest rate, which consists of contractual interest under the terms of the modification agreement in addition to an adjustment for the accretion of computed impairment. TDRs are placed on nonaccrual status if they become 90 days past due as to principal or interest payments, or sooner if conditions warrant and measure impairment based on collateral values, if the loan is collateral dependent.
Impaired Loans	Impaired Loans Impaired loans include loans on nonaccrual status and TDRs. Loans are considered impaired when based on current information and events it is probable the Corporation will be unable to collect all amounts due in accordance with the original contractual terms of the loan agreements. Impaired loans are accounted for at the lower of the present value of expected cash flows discounted at the loan's original effective interest rate or the estimated fair value of the collateral, if the loan is collateral dependent. When the present value of expected cash flows or the fair value of collateral of an impaired loan in the originated loan portfolio is less than the amount of unpaid principal outstanding on the loan, the principal balance of the loan is reduced to its carrying value through either a specific allowance for loan losses or a partial charge-off of the loan balance.
Nonperforming Loans	Nonperforming Loans Nonperforming loans are comprised of loans for which the accrual of interest has been discontinued (nonaccrual loans, including nonaccrual TDRs). Acquired loans that were classified as nonperforming loans prior to being acquired and acquired loans that are not performing in accordance with contractual terms subsequent to acquisition are not classified as nonperforming loans subsequent to acquisition because the loans are recorded in pools at net realizable value based on the principal and interest the Corporation expects to collect on such loans. They continue to earn interest from accretable yield, independent of performance in accordance of their contractual terms, and are expected to be fully collected under the new carrying values of such loans (that is, the new cost basis arising out of purchase accounting).
Allowance for Loan Losses	Allowance for Loan Losses The allowance for credit losses ("allowance") consists of two components: the allowance for loan losses (including both the originated and acquired loan portfolios) and the reserve for unfunded credit commitments. Unfunded credit commitments include items such as letters of credit, financial guarantees and binding unfunded loan commitments. The allowance represents management’s estimate of probable credit losses inherent in the loan and credit commitment portfolios as of period end. The allowance is calculated with the objective of maintaining a reserve sufficient to absorb losses inherent in the loan portfolio. The determination of the amount of the allowance requires significant judgment and the use of estimates related to the amount and timing of expected cash flows on acquired loans and impaired loans, collateral values on impaired loans, and estimated losses on pools of homogeneous loans based on historical loss experience, and consideration of current economic trends and conditions, all of which may be susceptible to significant change. The principal assumption used in deriving the allowance is the estimate of a loss percentage for each type of loan. In determining the allowance for the originated loan portfolio and the related provision for loan losses, the Corporation considers three principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans, (ii) reserves, by loan classes, on all other loans based on a six-year historical loan loss experience, loan loss trends and giving consideration to estimated loss emergence periods, and (iii) a reserve for qualitative factors that take into consideration risks inherent in the originated loan portfolio that differ from historical loan loss experience. The first element reflects the Corporation's estimate of probable losses based upon the systematic review of individually impaired loans in the originated loan portfolio. These estimates are based upon a number of objective factors, such as payment history, financial condition of the borrower and discounted collateral exposure. The Corporation measures the investment in an impaired loan based on one of three methods: the loan's observable market price; the fair value of the collateral; or the present value of expected future cash flows discounted at the loan's effective interest rate. Loans in the commercial loan portfolio that were in nonaccrual status (including nonaccrual TDRs) were valued based on the fair value of the collateral securing the loan, while accruing TDRs in the commercial loan portfolio and consumer loans were valued based on the present value of expected future cash flows discounted at the loan's effective interest rate. It is the Corporation's general policy to obtain new appraisals at initial impairment and updated when deemed necessary on nonaccrual loans in the commercial loan portfolio. Appraisals on nonaccrual loans in the consumer loan portfolio are updated at initial impairment and when deemed necessary where there is a delay in the foreclosure process. When the Corporation determines that the fair value of the collateral is less than the carrying value of an impaired loan and a portion is deemed not collectible, the portion of the impairment that is deemed not collectible is charged off (confirmed loss) and deducted from the allowance. The remaining carrying value of the impaired loan is classified as a nonperforming loan. When the Corporation determines that the fair value of the collateral is less than the carrying value of an impaired loan but believes it is probable it will recover this impairment, the Corporation establishes a valuation allowance for such impairment. The second element is determined by assigning allocations based principally upon a six -year average of loss experience for each class of loan. Average losses may be adjusted based on current loan loss experience, delinquency trends, estimated loss emergence periods and other industry specific environmental factors. This component considers the lagging impact of historical charge-off ratios in periods where future loan charge-offs are expected to increase or decrease, trends in delinquencies and nonaccrual loans, the changing portfolio mix in terms of collateral, average loan balance, loan growth and the degree of seasoning in the various loan portfolios. Loan loss analyses are performed quarterly and certain inputs and parameters are updated as necessary to reflect the current credit environment. The third element is based on qualitative factors that cannot be associated with a specific credit or loan class and reflects an attempt to ensure that the overall allowance appropriately reflects additional losses that are inherent in the Corporation's loan portfolio. Determination of the probable losses inherent in the portfolio, which are not necessarily captured by the allocation methodology discussed above, involves the exercise of judgment. This qualitative portion of the allowance is judgmentally determined and generally serves to compensate for the uncertainty in estimating inherent losses, particularly in times of changing economic conditions, and also considers the inherent judgment associated with risk rating commercial loans. The qualitative portion of the allowance also takes into consideration, among other things, economic conditions within our geographic areas and nationwide, including unemployment levels, industry-wide and Corporation specific loan delinquency rates, changes in composition of and growth in the Corporation's loan portfolio and changing commercial and residential real estate values. Consumer loans secured by real estate are charged-off to the estimated fair value of the collateral when a loss is confirmed or at 180 days past due, whichever is sooner. Loss confirming events include, but are not limited to, bankruptcy (unsecured), continued delinquency, foreclosure or receipt of an asset valuation indicating a collateral deficiency and the asset is the sole source of repayment. For consumer loans not secured by real estate, the charge-off is taken upon confirmation or 120 days past due. Commercial loans are evaluated on a loan level basis and either charged-off or written down to net realizable value if a loss confirming event has occurred. Loss confirming events include, but are not limited to, bankruptcy (unsecured), continued delinquency, foreclosure, or receipt of an asset valuation indicating a collateral deficiency and that asset is the sole source of repayment. Although the Corporation allocates portions of the allowance to specific loans and loan types, the entire allowance attributable to originated loans is available for any loan losses that occur in the originated portfolio. Loans that are deemed not collectible are charged off and reduce the allowance. The provision for loan losses and recoveries on loans previously charged off increase the allowance. Collection efforts may continue and recoveries may occur after a loan is charged off. Acquired loans are aggregated into pools based upon common risk characteristics. An allowance may be recorded related to an acquired loan pool if it experiences a decrease in expected cash flows, as compared to those projected at the acquisition date. On a quarterly basis, the expected future cash flow of each pool is estimated based on various factors, including changes in property values of collateral dependent loans, default rates, loss severities and prepayment speeds. Decreases in estimates of expected cash flows within a pool generally result in a charge to the provision for loan losses and a corresponding increase in the allowance allocated to acquired loans for the particular pool. Increases in estimates of expected cash flows within a pool generally result in a reduction in the allowance allocated to acquired loans for the particular pool, if applicable, and then an adjustment to the accretable yield for the pool, which will increase amounts recognized in interest income in subsequent periods. Various regulatory agencies, as an integral part of their examination processes, periodically review the allowance. Such agencies may require additions to the allowance, based on their judgment, reflecting information available to them at the time of their examinations.
Mortgage Banking Operations	Mortgage Banking Operations The Corporation generally sells conforming long-term fixed interest rate mortgage loans it originates in the secondary market. Gains on the sales of these loans are determined using the specific identification method. The Corporation sells residential mortgage loans in the secondary market on either a servicing retained or released basis. The Corporation elected the fair value measurement option, as prescribed by ASC Topic 820, Fair Value Measurements and Disclosures ("ASC 820"), for all residential mortgage loans held-for-sale originated on or after July 1, 2012. This election allows for a more effective offset of the changes in fair value of residential mortgage loans held-for-sale and the derivative instruments used to economically hedge them without having to apply complex hedge accounting provisions. Residential mortgage loans held-for-sale are carried at fair value, with changes in fair value recorded through earnings. Residential mortgage loan commitments, forward commitments, are generally entered into at the time customer applications are accepted to protect the value of the mortgage loans from increases in market interest rates during the period held and are generally settled with the investor in the secondary market within 90 days after entering into the forward commitment. Forward loan commitments are accounted for as derivatives and recorded at fair value, with changes in fair value recorded through earnings. The Corporation recognizes revenue associated with the expected future cash flows of servicing loans for loans held-for-sale at the time a forward loan commitment is made to originate a held-for-sale loan, as required under SEC Staff Accounting Bulletin No. 109, Written Loan Commitments Recorded at Fair Value through Earnings. The Corporation purchases and originates loans for sale to the secondary market and sell the loans on either a servicing retained or servicing-released basis. If we retain the right to service the loan, a loan servicing rights ("LSRs") is created at the time of sale which is recorded at fair value. Effective January 1, 2017, the Corporation elected to account for all LSRs previously accounted for under the lower of cost or fair value method under the fair value method. Management believes this election will provide more comparable results to peers as many of those within our industry group account for loan servicing rights under the fair value method. The change in accounting policy in the first quarter of 2017 resulted in a cumulative adjustment to increase retained earnings in the amount of $3.7 million , net of taxes. LSRs are established and recorded at the estimated fair value by calculating the present fair value of estimated future net servicing cash flows. To determine the fair value of LSRs, the Corporation uses an independent third party valuation model requiring the incorporation of assumptions that market participants would use in estimating future net servicing income, which include estimates of prepayment speeds, discount rate, cost to service and escrow account earnings. Changes in the fair value of LSRs directly impact earnings. Servicing income is recognized in net gain on sale of loans and other mortgage banking revenue in the Consolidated Statements of Income when earned and is offset by the fair value of LSRs.
Derivatives	Derivatives The Corporation enters into derivative to manage the fair value changes, exposure to fluctuations exposed to price and interest rate risk, facilitate asset/liability management, minimize the variability of future cash flows on long-term debt, and to provide a service to certain qualifying customers to help facilitate their respective risk management strategies ("customer-initiated derivatives"). All derivatives are recognized on the Consolidated Statements of Financial Condition as other assets and liabilities, as applicable, at their estimated fair value. For derivatives designated as qualified cash flow hedges, changes in the fair value of the derivatives, to the extent effective as a hedge, are recorded in accumulated other comprehensive income, net of income taxes, and reclassified into earnings concurrently with the earnings of the hedged item. For customer-initiated and mortgage banking derivatives, changes in the fair value of the derivative are recognized immediately in earnings. Interest rate swaps are entered into in order to economically hedge the effect of changes and to mitigate the impact of fluctuations in interest rate volatility to manage exposures that arise from business activities that result in the receipt or payment of future known and uncertain cash amounts. These derivatives are designated as cash flow hedges. Accordingly, the effective portion of changes in the fair value of interest rate swaps are recorded in accumulated other comprehensive income on the Consolidated Statement of Financial Condition and is subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. Any ineffective portion of the change in fair value of the derivatives is recognized directly in earnings. The Corporation expects the hedges to remain highly effective during the remaining terms of the swaps. Interest rate swaps, are valued based on quoted prices for similar assets in an active market with inputs that are observable. The Corporation utilizes interest rate derivatives to provide a service to certain qualifying customers to help facilitate their respective risk management strategies, customer-initiated derivatives. Therefore, these derivatives are not used to manage interest rate risk in the Corporation's assets or liabilities. The Corporation generally takes offsetting positions with dealer counterparties to mitigate the valuation risk of the customer-initiated derivatives. Income primarily results in the spread between the customer derivatives and offsetting dealer positions. The gains or losses derived from changes in fair value are recognized in current earnings during the period of change in other noninterest income on the Consolidated Statements of Income. The Corporation calculates a credit valuation adjustment by applying a credit spread for the counterparty or the Corporation, as appropriate, to the total expected exposure of the derivative after considering collateral and other master netting arrangements. The Corporation additionally has written and purchased option derivatives consisting of instruments to facilitate an equity-linked time deposit product (the "Power Equity CD"). The Power Equity CD is a time deposit that provides the purchaser a guaranteed return of principal at maturity plus a potential equity return (a written option), while the Corporation receives a known stream of funds based on the equity return (a purchased option). The written and purchased options are mirror derivative instruments which are carried at fair value on the Consolidated Statements of Financial Position.
Premises and Equipment	Premises and Equipment Land is carried at cost. Premises and equipment are stated at cost less accumulated depreciation. Depreciation is computed using the straight-line method with useful lives ranging from 25 to 40 years for buildings and three to ten years for all other depreciable assets. Maintenance and repairs are charged to expense as incurred.
Other Real Estate Owned and Repossessed Assets	Other Real Estate Owned and Repossessed Assets Other real estate owned ("ORE") and repossessed assets represent property acquired by the Corporation as part of an acquisition or subsequently through the loan foreclosure or repossession process, or any other resolution activity that results in partial or total satisfaction of problem loans. ORE is primarily comprised of commercial and residential real estate properties, including vacant land and development properties, obtained in partial or total satisfaction of loan obligations. The acquired properties are recorded at fair value at the date of acquisition. Losses arising at the time of acquisition of properties not acquired as part of an acquisition are charged against the allowance for loan and lease losses. Foreclosed properties are initially recorded at the lower of cost, or the estimated fair value of the property, less estimated costs to sell, based upon the property's appraised value at the date of transfer to ORE and management's estimate of the fair value of the collateral, establishing a new cost basis. Any difference between the net realizable value of the property and the carrying value of the loan is charged to the allowance for loan losses. Subsequently, all other real estate owned is valued at the lower of cost or fair value, less estimated costs to sell, based on periodic valuations performed by management, with any difference between the net realizable value of the property and the carrying value of the loan charged to the allowance for loan losses. If fair value declines subsequent to foreclosure, a valuation allowance is recorded through expense. Subsequent write-downs, for amounts not expected to be recovered, in the carrying value of other real estate owned and repossessed asset properties that may be required are expensed as incurred. Improvements to the properties may be capitalized if the improvements contribute to the overall value of the property. Improvement amounts may not be capitalized in excess of the net realizable value of the property. Any gains or losses realized at the time of disposal are reflected in other noninterest expense on the Consolidated Statements of Income. Other real estate owned and repossessed assets totaling $8.8 million and $17.2 million at December 31, 2017 and 2016 , respectively, was included in "Interest receivable and other assets" in the Consolidated Statements of Financial Position.
Goodwill	Goodwill Goodwill is not amortized, but rather is subject to impairment tests annually or more frequently if triggering events occur and indicate potential impairment. The Corporation's annual goodwill impairment assessment was performed as of October 31, 2017 . The Corporation elected to utilize the qualitative assessment of goodwill impairment allowed under ASC Topic 350-20, Goodwill ("ASC 350-20") that became acceptable as a result of FASB Accounting Standards Update ("ASU") 2011-08, Testing Goodwill for Impairment. In accordance with ASC 350-20, the Corporation assessed qualitative factors to determine whether it is more likely than not that the fair value of its reporting units were less than their carrying amounts. In evaluating whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount, the Corporation assesses relevant events and circumstances, including macroeconomic conditions, industry and market considerations, overall financial performance, changes in the composition or carrying amount of assets and liabilities, the market price of the Corporation's common stock, and other relevant factors. Based on the qualitative assessment performed, the Corporation determined that no goodwill impairment was evident as of the October 31, 2017 assessment date. The Corporation also determined that no triggering events occurred that indicated impairment from the most recent assessment date through December 31, 2017 and that the Corporation's goodwill was not impaired at December 31, 2017 .
Other Intangible Assets	Other Intangible Assets Intangible assets consist of core deposit intangible assets and non-compete intangible assets. Core deposit intangible assets arose as the result of business combinations or other acquisitions and are amortized over periods ranging from 10 to 15 years , primarily on an accelerated basis, as applicable. Non-compete intangible assets arose as the result of business combinations and are amortized over the period of the non-compete agreements. Intangible assets are tested for impairment on an annual basis in accordance with ASC Topic 350, "Intangibles-Goodwill and Other.
Share-based Compensation	Share-based Compensation The Corporation grants stock options, Time-Based Restricted Stock Units ("TRSUs"), Performance-Based Restricted Stock Units ("PRSUs"), and other stock awards to certain executive and senior management employees. The Corporation accounts for share-based compensation expense using the modified-prospective transition method. Under that method, compensation expense is recognized for stock options based on the estimated grant date fair value as computed using the Black-Scholes option pricing model and the probability of issuance. The Corporation accounts for stock awards based on the closing stock price of the Corporation's common stock on the date the award is granted. The fair values of stock options, stock awards and restricted stock awards are recognized as compensation expense on a straight-line basis over the requisite service period. The Corporation accounts for PRSUs based on the closing stock price of the Corporation's common stock on the date of grant, discounted by the present value of estimated future dividends to be declared over the requisite performance or service period. The fair value of PRSUs is recognized as compensation expense over the expected requisite performance period, or requisite service period for awards with multiple performance and service conditions. The Corporation accounts for TRSUs based on the closing stock price of the Corporation's common stock on the date of grant, as these awards accrue dividend equivalents equal to the amount of any cash dividends that would have been payable to a shareholder owning the number of shares of the Corporation's common stock represented by the TRSUs. The fair value of the TRSUs is recognized as compensation expense over the requisite service period.
Bank-Owned Life Insurance	Bank-Owned Life Insurance The Corporation has life insurance policies on certain key officers of Chemical Bank. The majority of the bank-owned life insurance policies of the Corporation were obtained through its acquisition of Lake Michigan and the merger with Talmer. Bank-owned life insurance is recorded at the cash surrender value, net of surrender charges, and is included within "Interest receivable and other assets" on the Consolidated Statements of Financial Position and tax-exempt income from the periodic changes in the cash surrender values are recorded as "Other noninterest income" on the Consolidated Statements of Income.
Securities Sold Under Agreements to Repurchase with Customers	Securities Sold Under Agreements to Repurchase with Customers Securities sold under agreements to repurchase with customers are collateralized financing transactions and the obligations to repurchase securities sold are reflected as a liability in the accompanying Consolidated Statements of Financial Position. The dollar amount of the securities underlying the agreements remains in the Corporation's investment securities portfolio. The Corporation's securities sold under agreements to repurchase with customers are considered a stable source of liquidity, much like its core deposit base, and are generally only provided to customers that have an established banking relationship with Chemical Bank.
Short-term Borrowings	Short-term Borrowings Short-term borrowings are comprised of short-term FHLB advances with original scheduled maturities of one year or less. From time to time, the Corporation may also utilized federal funds purchased, which represent unsecured borrowings from nonaffiliated third-party financial institutions, generally on an overnight basis, to cover short-term liquidity needs.
Long-term Borrowings	Long-term Borrowings Long-term borrowings are comprised of securities sold under agreements to repurchase with an unaffiliated third-party financial institution, a secured non-revolving line-of-credit with an unaffiliated third-party financial institution, subordinated debentures and long-term FHLB advances. Securities sold under agreements to repurchase are collateralized financing transactions and the obligations to repurchase securities sold are reflected as a liability in the accompanying Consolidated Statements of Financial Position. The dollar amount of the securities underlying the agreements remains in the Corporation's investment securities portfolio. FHLB advances, both short-term and long-term, are borrowings from the FHLB to fund short-term liquidity needs as well as a portion of the loan and investment securities portfolios. These advances are secured, under a blanket security agreement, by first lien residential mortgage loans with an aggregate book value equal to at least 140.0% of the FHLB advances and the FHLB stock owned by the Corporation. FHLB advances with an original maturity of one year or less are classified as short-term and FHLB advances with an original maturity of more than one year are classified as long-term.
Fair Value Measurements	Fair Value Measurements Fair value for assets and liabilities measured at fair value on a recurring or nonrecurring basis refers to the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants in the market in which the reporting entity transacts such sales or transfers based on the assumptions market participants would use when pricing an asset or liability. Assumptions are developed based on prioritizing information within a fair value hierarchy that gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data, such as the reporting entity's own data. The Corporation may choose to measure eligible items at fair value at specified election dates. Unrealized gains and losses on items for which the fair value measurement option has been elected are reported in earnings at each subsequent reporting date. At December 31, 2017 and 2016 , the Corporation had elected the fair value option on all of its residential mortgage loans held-for-sale. In addition, the Corporation elected to account for loan servicing rights under the fair value method effective January 1, 2017. The Corporation has not elected the fair value option for any other financial assets or liabilities as of December 31, 2017 .
Pension and Postretirement Benefit Plan Actuarial Assumptions	Pension and Postretirement Benefit Plan Actuarial Assumptions The Corporation's defined benefit pension, supplemental pension and postretirement benefit obligations and related costs are calculated using actuarial concepts and measurements. Two critical assumptions, the discount rate and the expected long-term rate of return on plan assets, are important elements of expense and/or benefit obligation measurements. Other assumptions involve employee demographic factors such as retirement patterns, mortality, turnover and the rate of future compensation increases, as well as future health care costs. The Corporation evaluates all assumptions annually. The discount rate enables the Corporation to state expected future benefit payments as a present value on the measurement date. The Corporation determined the discount rate at December 31, 2017 and 2016 by utilizing the results from a discount rate model that involves selecting a portfolio of bonds to settle the projected benefit payments of each plan. To determine the expected long-term rate of return on defined benefit pension plan assets, the Corporation considers the current asset allocation of the defined benefit pension plan, as well as historical and expected returns on each asset class. A lower expected rate of return on defined benefit pension plan assets will increase pension expense. The Corporation recognizes the over- or under-funded status of a plan within "Interest receivable and other assets" or "Interest payable and other liabilities" in the Consolidated Statements of Financial Position as measured by the difference between the fair value of the plan assets and the projected benefit obligation. Unrecognized prior service costs and actuarial gains and losses are recognized as a component of accumulated other comprehensive income (loss). The Corporation measures defined benefit plan assets and obligations as of December 31.
Advertising Costs	Advertising Costs Advertising costs are expensed as incurred.
Income and Other Taxes	Income and Other Taxes The Corporation is subject to the income and other tax laws of the United States, the States of Michigan, Ohio and Indiana and other states where nexus has been created. These laws are complex and are subject to different interpretations by the taxpayer and the various taxing authorities. In determining the provision for income and other taxes, management must make judgments and estimates about the application of these inherently complex laws, related regulations and case law. In the process of preparing the Corporation's tax returns, management attempts to make reasonable interpretations of enacted tax laws. These interpretations are subject to challenge by the tax authorities upon audit or to reinterpretation based on management's ongoing assessment of facts and evolving case law. The Corporation and its subsidiaries file a consolidated federal income tax return. The provision for federal income taxes is based on income and expenses, as reported in the Consolidated Financial Statements, rather than amounts reported on the Corporation's federal income tax return. The difference between the federal statutory income tax rate and the Corporation's effective federal income tax rate is primarily a function of the proportion of the Corporation's interest income exempt from federal taxation, nondeductible interest expense and other nondeductible expenses relative to pretax income and tax credits. When income and expenses are recognized in different periods for tax purposes than for book purposes, deferred tax assets and liabilities are recognized for the future tax consequences attributable to the temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Differences in the tax and book carrying amounts of assets and liabilities can also be generated when the Corporation acquires other banks or bank branches. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income or expense in the period that includes the enactment date of the change. On December 22, 2017, H.R.1, commonly referred to as the "Tax Cuts and Jobs Act" was signed into law. The Tax Cuts and Jobs Act, among other items, reduces the corporate income tax rate from 35% to 21%, effective January 1, 2018. As such, the Corporation completed a revaluation of the net deferred tax assets and estimated a reduction in the Corporation's deferred tax asset as of December 31, 2017 . On a quarterly basis, management assesses the reasonableness of its effective federal tax rate based upon its estimate of taxable income and the applicable taxes expected for the full year. Deferred tax assets and liabilities are reassessed on a quarterly basis, including the need for a valuation allowance for deferred tax assets. Uncertain income tax positions are evaluated to determine whether it is more-likely-than-not that a tax position will be sustained upon examination based on the technical merits of the tax position. If a tax position is more-likely-than-not to be sustained, a tax benefit is recognized for the amount that is greater than 50.0% likely to be realized. Reserves for contingent income tax liabilities attributable to unrecognized tax benefits associated with uncertain tax positions are reviewed quarterly for adequacy based upon developments in tax law and the status of audits or examinations. The Corporation had no contingent income tax liabilities recorded at December 31, 2017 and 2016 .
Investments in Qualified Affordable Housing Projects, Federal Historic Projects and New Market Tax Credits	Investments in Qualified Affordable Housing Projects, Federal Historic Projects and New Market Tax Credits The Corporation invests in qualified affordable housing projects, federal historic projects, and new market projects for the purpose of community reinvestment and obtaining tax credits. Return on the Corporation's investment in these projects comes in the form of the tax credits and tax losses that pass through to the Corporation. The carrying value of the investments is reflected in "Interest receivable and other assets" on the Consolidated Statements of Financial Position. The Corporation utilizes the proportional amortization method to account for investments in qualified affordable housing projects and the equity method to account for investments in other tax credit projects. Management analyzes these investments for potential impairment when events or changes in circumstances indicate that it is more-likely-than-not that the carrying amount of the investment will not be realized. An impairment loss is measured as the amount by which the carrying amount of an investment exceeds its fair value. Under the proportional amortization method, the Corporation amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits. Under the equity method, the Corporation's share of the earnings or losses is included in "Other operating expenses" on the Consolidated Statements of Income. The Corporation's unfunded equity contributions relating to investments in qualified affordable housing projects, federal historic tax projects and new market projects is recorded in "Interest payable and other liabilities" on the Consolidated Statements of Financial Position.
Earnings Per Share	Earnings Per Share The Corporation applies the two-class method of computing earnings per share as the Corporation has unvested restricted stock awards which qualify as participating securities. Under this calculation, all outstanding unvested share-based payment awards that contain rights to nonforfeitable dividends are considered participating securities and earnings per share is determined according to dividends declared and participating right in undistributed earnings.
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Comprehensive income of the Corporation includes net income and adjustments to shareholders' equity for changes in unrealized gains and losses on investment securities available-for-sale and changes in the net actuarial gain/loss for the Corporation's defined benefit pension and postretirement plans, net of income taxes. The Corporation presents "Comprehensive income" as a component in the Consolidated Statements of Changes in Shareholders' Equity and the components of other comprehensive income separately in the Consolidated Statements of Comprehensive Income.
Reclassifications	Reclassifications Certain amounts appearing in the Consolidated Financial Statements and notes thereto for prior periods have been reclassified to conform to the current presentation. The reclassification had no effect on net income or shareholders’ equity as previously reported.
Adopted Accounting Pronouncements	Adopted Accounting Pronouncements Stock Compensation In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), which simplifies the accounting for employee share-based payment transactions including the accounting for income taxes, forfeitures and statutory holding requirements, as well as classification on the statement of cash flows. ASU 2016-09 is effective for public companies for interim and annual periods beginning after December 15, 2016 with early adoption permitted for any interim or annual period. If an entity early adopts the amendments, any adjustment should be reflected as of the beginning of the fiscal year. The Corporation elected to early adopt ASU 2016-09 during the fourth quarter of 2016. All quarters during the year ended December 31, 2016 have been adjusted as a result of this adoption. Prior to adoption of ASU 2016-09, all excess tax benefits resulting from the exercise or settlement of share-based payment transactions were recognized in additional-paid-in-capital ("APIC") and accumulated in an APIC pool, while tax deficiencies were either offset against the APIC pool or recognized in the income statement if no APIC pool was available. The new guidance eliminates additions to the APIC pool and all excess tax benefits and deficiencies are recognized as an income tax benefit or expense in the income statement prospectively. Accordingly, periods prior to January 1, 2016 have not been adjusted. Investment Securities The Corporation elected to early adopt ASU No. 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities ("ASU 2017-08") during the second quarter of 2017. The guidance in ASU 2017-08 shortens the amortization period for certain callable debt securities that are held at a premium to the earliest call date. Debt securities held at a discount will continue to be amortized as a yield adjustment over the life of the instrument. The early adoption of ASU 2017-08 in the second quarter of 2017 did not have a material impact on the Consolidated Financial Statements. Accumulated Other Comprehensive Income (Loss) The Corporation elected to early adopt ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income ("ASU 2018-02") during the fourth quarter 2017. In February 2018, the FASB issued ASU 2018-02, which requires deferred tax liabilities and assets to be adjusted for the effect of a change in tax laws or rates with the effect included in income from continuing operations in the reporting period that includes the enactment date and permitted early adoption. The Corporation elected to early adopt ASU 2018-02 during the fourth quarter of 2017 and an election was made to reclassify the income tax effects of the Tax Cuts and Jobs Act from accumulated other comprehensive income to retained earnings. The early adoption of ASU 2018-02, resulted in a $4.5 million reclassification from accumulated other comprehensive income to retained earnings related to the income tax effects of the Tax Cuts and Jobs Act.

Mergers and Acquisitions (Table

Mergers and Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Summary of assets acquired and liabilities assumed	(Dollars in thousands) Stock $ 26,988 Cash 203 Total consideration $ 27,191 Net assets acquired: Monarch shareholders' equity $ 15,270 Adjustments to reflect fair value of net assets acquired: Loans (7,150 ) Allowance for loan losses 2,128 Deferred tax assets, net: Net operating loss carryforward 7,900 Other 1,826 Premises and equipment (415 ) Core deposit intangibles 1,930 Mortgage servicing rights 315 Other assets and other liabilities 48 Fair value of adjusted net assets acquired 21,852 Goodwill recognized as a result of the Monarch transaction $ 5,339 (Dollars in thousands) Stock $ 132,916 Cash 54,478 Total consideration 187,394 Net assets acquired: Lake Michigan shareholders' equity $ 89,280 Adjustments to reflect fair value of net assets acquired: Loans (22,600 ) Allowance for loan losses 15,888 Premises and equipment (5,031 ) Core deposit intangibles 8,003 Deferred tax assets, net 4,096 Deposits and borrowings, net (3,182 ) Other assets and other liabilities (121 ) Fair value of adjusted net assets acquired 86,333 Goodwill recognized as a result of the Lake Michigan transaction $ 101,061 The following schedule summarizes the acquisition date fair values of assets acquired and liabilities assumed from Lake Michigan: (Dollars in thousands) Assets Cash and cash equivalents $ 39,301 Investment securities 66,699 Loans 985,542 Premises and equipment 10,975 Deferred tax asset, net 16,715 Goodwill 101,061 Core deposit intangible asset 8,003 Bank-owned life insurance 23,844 Other assets 37,695 Assets acquired, at fair value 1,289,835 Liabilities Deposits 924,697 Short-term borrowings 30,000 Other borrowings 124,857 Other liabilities 22,887 Total liabilities acquired, at fair value 1,102,441 Total purchase price $ 187,394 Fair values were determined in accordance with the guidance provided in ASC Topic 820, Fair Value Measurements, as of the merger date as presented in the following table. (Dollars in thousands) Consideration paid: Stock $ 1,504,811 Cash 107,638 Total consideration 1,612,449 Fair value of identifiable assets acquired (1) : Cash and cash equivalents 433,352 Investment securities: Available-for-sale 808,894 Held-to-maturity 1,657 Loans held-for-sale 244,916 Loans 4,882,402 Premises and equipment 38,793 Loan servicing rights 42,462 Other intangible assets 19,088 Interest receivable and other assets (2) 395,539 Total identifiable assets acquired 6,867,103 Fair value of liabilities assumed (1) : Noninterest-bearing deposits 1,236,902 Interest-bearing deposits 4,057,716 Interest payable and other liabilities (2) 100,936 Securities sold under agreements to repurchase with customers 19,704 Short-term borrowings 387,500 Long-term borrowings 299,597 Total liabilities assumed 6,102,355 Fair value of net identifiable assets acquired 764,748 Goodwill resulting from acquisition (2) $ 847,701 (1) All amounts were previously reported in the Corporation's Annual Report on Form 10-K for the year ended December 31, 2016, with the exception of interest receivable and other assets and interest payable and other liabilities. (2) Includes adjustments to the fair value as a result of additional valuation information obtained during the third quarter of 2017, including the corresponding tax effects. The following schedule summarizes the revised acquisition date estimated fair values, including the adjustments to the fair values identified and recorded from the acquisition date through December 31, 2015, of assets acquired and liabilities assumed from Monarch. (Dollars in thousands) Assets Cash and cash equivalents $ 32,171 Loans 121,783 Premises and equipment 3,019 Deferred tax assets, net Net operating loss carryforward 7,900 Other 2,392 Interest receivable and other assets 6,972 Goodwill 5,339 Core deposit intangibles 1,930 Mortgage servicing rights 1,284 Assets acquired, at fair value 182,790 Liabilities Deposits 144,300 FHLB advances 8,000 Interest payable and other liabilities 3,299 Total liabilities acquired, at fair value 155,599 Total purchase price $ 27,191
Information regarding acquired loans accounted for under ASC 310-30	Information regarding loans accounted for under ASC 310-30 at the merger date is as follows: (Dollars in thousands) Accounted for under ASC 310-30: Contractual cash flows $ 5,968,488 Contractual cash flows not expected to be collected (nonaccretable difference) 223,959 Expected cash flows 5,744,529 Interest component of expected cash flows (accretable yield) 862,127 Fair value at acquisition $ 4,882,402 Information regarding loans accounted for under ASC 310-30 at the merger date is as follows: (Dollars in thousands) Accounted for under ASC 310-30: Contractual cash flows $ 1,198,388 Contractual cash flows not expected to be collected (nonaccretable difference) 22,600 Expected cash flows 1,175,788 Interest component of expected cash flows (accretable yield) 190,246 Fair value at acquisition $ 985,542 Information regarding loans accounted for under ASC 310-30 at the merger date is as follows: (Dollars in thousands) Accounted for under ASC 310-30: Contractual cash flows $ 166,797 Contractual cash flows not expected to be collected (nonaccretable difference) 7,100 Expected cash flows 159,697 Interest component of expected cash flows (accretable yield) 37,914 Fair value at acquisition $ 121,783
Pro forma financial information	The following unaudited pro forma financial information presents the consolidated results of operation of the Corporation and Talmer as if the merger had occurred as of January 1, 2015 and Lake Michigan and Monarch as if the acquisitions had occurred as of January 1, 2014. The unaudited pro forma combined results of operations are presented solely for information purposes and are not intended to represent or be indicative of the consolidated results of operations that Chemical would have reported had these transactions been completed as of the dates and for the periods presented, nor are they necessarily indicative of future results. In particular, no adjustments have been made to eliminate the amount of Talmer's, Lake Michigan's or Monarch's provision for loan losses incurred prior to the acquisition date that would not have been necessary had the acquired loans been recorded at fair value as of the beginning of each period indicated. In accordance with Article 11 of SEC Regulation S-X, transaction costs directly attributable to the acquisitions have been excluded. Years ended December 31, (In thousands, except per share data) 2017 2016 2015 Net interest and other income $ 701,597 $ 492,323 $ 654,962 Net Income 149,523 115,847 142,504 Earnings per share: Basic $ 2.11 $ 1.65 $ 2.03 Diluted $ 2.08 $ 1.62 $ 2.01

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Summary of assets measured at fair value on a recurring basis	s and liabilities measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets and liabilities follow: (Dollars in thousands) Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total December 31, 2017 Investment securities — available-for-sale: Government sponsored agencies $ — $ 202,916 $ — $ 202,916 State and political subdivisions — 345,970 — 345,970 Mortgage-backed securities — 150,131 — 150,131 Collateralized mortgage obligations — 1,033,845 — 1,033,845 Corporate bonds — 192,794 — 192,794 Preferred stock and trust preferred securities — 37,890 — 37,890 Total investment securities — available-for-sale — 1,963,546 — 1,963,546 Loans held-for-sale — 52,133 — 52,133 Loan servicing rights — — 63,841 63,841 Derivative assets: Customer-initiated derivatives — 9,376 — 9,376 Interest rate lock commitments — 1,222 — 1,222 Power Equity CD — 2,184 — 2,184 Risk management derivatives — 5,899 — 5,899 Total derivatives — 18,681 — 18,681 Total assets at fair value $ — $ 2,034,360 $ 63,841 $ 2,098,201 Derivative liabilities: Customer-initiated derivatives $ — $ 10,139 $ — $ 10,139 Forward contracts related to mortgage loans to be delivered for sale — 34 — 34 Power Equity CD — 2,184 — 2,184 Total derivatives — 12,357 — 12,357 Total liabilities at fair value $ — $ 12,357 $ — $ 12,357 (Dollars in thousands) Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total December 31, 2016 Investment securities — available-for-sale: U.S. Treasury securities $ 5,793 $ — $ — $ 5,793 Government sponsored agencies — 215,011 — 215,011 State and political subdivisions — 300,088 — 300,088 Residential mortgage-backed securities — 272,282 — 272,282 Collateralized mortgage obligations — 320,025 — 320,025 Corporate bonds — 89,474 — 89,474 Preferred stock and trust preferred securities — 32,291 — 32,291 Total investment securities — available-for-sale 5,793 1,229,171 — 1,234,964 Loans held-for-sale — 81,830 — 81,830 Loan servicing rights — — 48,085 48,085 Derivative assets: Customer-initiated derivatives — 4,406 — 4,406 Forward contracts related to mortgage loans to be delivered for sale — 635 — 635 Interest rate lock commitments — 956 — 956 Power Equity CD — 2,218 — 2,218 Total derivatives — 8,215 — 8,215 Total assets at fair value $ 5,793 $ 1,319,216 $ 48,085 $ 1,373,094 Derivative liabilities: Customer-initiated derivatives — 4,141 — 4,141 Power Equity CD — 2,218 — 2,218 Total derivatives — 6,359 — 6,359 Total liabilities at fair value $ — $ 6,359 $ — $ 6,359 There
Summary of changes in Level 3 assets measured at fair value on a recurring basis	wing table summarizes the changes in Level 3 assets measured at fair value on a recurring basis. Year Ended December 31, 2017 2016 (Dollars in thousands) Loan servicing rights Balance, beginning of period $ 48,085 $ — Additions due to acquisition — 42,462 Transfer in based on new accounting policy election (1) 15,891 — Gains (losses): Recorded in earnings (realized): Recorded in "Net gain on sale of loans and other mortgage banking revenue" (8,880 ) 4,593 New originations 8,745 1,030 Balance, end of period $ 63,841 $ 48,085 (1) Refe
Schedule of aggregate fair value contractual balance and gain (loss) for loans held-for-sale	gate fair value, contractual balance (including accrued interest), and gain or loss for loans held-for-sale carried at fair value option was as follows: December 31, (Dollars in thousands) 2017 2016 Aggregate fair value $ 52,133 $ 81,830 Contractual balance 50,597 81,009 Unrealized gain (loss) 1,536 821 The to
Amount of gains (losses) from loans held for sale included in the Consolidated Statements of Income	amount of gains (losses) from loans held-for-sale included in the Consolidated Statements of Income was as follows: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Interest income (1) $ 2,540 $ 1,606 $ 83 Change in fair value (2) 715 39 (61 ) Net gain on sales of loans (2) 31,734 15,686 6,354 Total included in earnings $ 34,989 $ 17,331 $ 6,376 (1) Included in "Interest and fees on loans" in the Consolidated Statements of Income. (2) Included in "Net gain on sale of loans and other mortgage banking revenue" in the Consolidated Statements of Income. Assets
Summary of assets measured at fair value on a nonrecurring basis	s measured at fair value on a nonrecurring basis, quantitative disclosures about fair value measurements for each major category of assets follow: (Dollars in thousands) Significant Unobservable Inputs (Level 3) Total December 31, 2017 Impaired loans $ 70,619 $ 70,619 Other real estate and repossessed assets 2,899 2,899 Total $ 73,518 $ 73,518 December 31, 2016 Impaired loans $ 62,184 $ 62,184 Other real estate and repossessed assets 1,386 1,386 Loan servicing rights 2 2 Total $ 63,572 $ 63,572 There w
Additional information about significant unobservable inputs used in the fair value measurement of financial assets	wing table presents additional information about the significant unobservable inputs used in the fair value measurement of financial assets measured on a nonrecurring basis that were categorized within the Level 3 of the fair value hierarchy: (Dollars in thousands) Fair Value at December 31, 2017 Valuation Technique Significant Unobservable Inputs Range Impaired loans $ 70,619 Appraisal of collateral Discount for type of collateral and age of appraisal 20%-30% Other real estate and repossessed assets 2,899 Appraisal of property Discount for type of property and age of appraisal 20%-30% Disclosu
Summary of carrying amounts and estimated fair values of the financial instruments	of carrying amounts and estimated fair values of the Corporation's financial instruments not recorded at fair value in their entirety on a recurring basis on the Consolidated Statements of Financial Position was as follows: December 31, Level in Fair Value Measurement Hierarchy 2017 2016 (Dollars in thousands) Carrying Amount Fair Value Carrying Amount Fair Value Financial assets: Cash and cash equivalents Level 1 $ 455,991 $ 455,991 $ 474,402 $ 474,402 Investment securities: Held-to-maturity Level 2 676,593 662,516 622,927 608,221 Held-to-maturity Level 3 500 390 500 310 Nonmarketable equity securities Level 2 180,091 180,091 97,350 97,350 Net loans (1) Level 3 14,063,380 14,114,545 12,912,511 13,069,315 Interest receivable Level 2 50,710 50,710 42,235 42,235 Bank-owned life insurance Level 2 147,584 147,584 143,718 143,718 Financial liabilities: Deposits: Deposits without defined maturities Level 2 $ 10,425,596 $ 10,425,596 $ 9,862,755 $ 9,862,755 Time deposits Level 2 3,217,207 3,225,847 3,010,367 3,010,048 Total deposits 13,642,803 13,651,443 12,873,122 12,872,803 Interest payable Level 2 6,329 6,329 5,415 5,415 Securities sold under agreements to repurchase with customers Level 2 415,236 415,236 343,047 343,047 Short-term borrowings Level 2 2,000,000 1,999,137 825,000 825,000 Long-term borrowings Level 2 372,882 367,984 597,847 591,227 (1) Included $70.6 million and $62.2 million of impaired loans recorded at fair value on a nonrecurring basis at December 31, 2017 and 2016 , respectively.

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities	The following is a summary of the amortized cost and fair value of investment securities available-for-sale and investment securities held-to-maturity at December 31, 2017 and 2016 : Investment Securities Available-for-Sale (Dollars in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2017 Government sponsored agencies $ 203,099 $ 765 $ 948 $ 202,916 State and political subdivisions 350,088 310 4,428 345,970 Residential mortgage-backed securities 151,752 5 1,626 150,131 Collateralized mortgage obligations 1,042,240 89 8,484 1,033,845 Corporate bonds 193,230 1,156 1,592 192,794 Preferred stock and trust preferred securities 36,237 1,715 62 37,890 Total $ 1,976,646 $ 4,040 $ 17,140 $ 1,963,546 December 31, 2016 U.S. Treasury securities $ 5,788 $ 5 $ — $ 5,793 Government sponsored agencies 216,890 189 2,068 215,011 State and political subdivisions 311,704 163 11,779 300,088 Residential mortgage-backed securities 276,162 112 3,992 272,282 Collateralized mortgage obligations 323,965 63 4,003 320,025 Corporate bonds 90,859 16 1,401 89,474 Preferred stock and trust preferred securities 31,353 1,018 80 32,291 Total $ 1,256,721 $ 1,566 $ 23,323 $ 1,234,964
Held-to-maturity Securities	Investment Securities Held-to-Maturity (Dollars in thousands) Amortized Cost Unrecognized Gains Unrecognized Losses Fair Value December 31, 2017 State and political subdivisions $ 676,593 $ 3,856 $ 17,933 $ 662,516 Trust preferred securities 500 — 110 390 Total $ 677,093 $ 3,856 $ 18,043 $ 662,906 December 31, 2016 State and political subdivisions $ 622,927 $ 2,648 $ 17,354 $ 608,221 Trust preferred securities 500 — 190 310 Total $ 623,427 $ 2,648 $ 17,544 $ 608,531
Proceeds from sales of securities and the associated gains and losses recorded in earnings	Proceeds from sales of securities and the associated gains and losses recorded in earnings are listed below: For the years ended December 31, (Dollars in thousands) 2017 2016 2015 Proceeds $ 409,220 $ 41,446 $ 40,301 Gross gains 178 325 631 Gross losses (7,566 ) (196 ) (1 )
Amortized cost and fair value of debt securities by contractual maturity	The following is a summary of the amortized cost and fair value of investment securities at December 31, 2017 , by maturity, for both available-for-sale and held-to-maturity investment securities. The maturities of residential mortgage-backed securities and collateralized mortgage obligations are based on scheduled principal payments. The maturities of all other debt securities are based on final contractual maturity. December 31, 2017 (Dollars in thousands) Amortized Cost Fair Value Investment Securities Available-for-Sale: Due in one year or less $ 300,364 $ 298,644 Due after one year through five years 751,998 746,082 Due after five years through ten years 616,027 611,822 Due after ten years 306,868 305,174 Preferred stock 1,389 1,824 Total $ 1,976,646 $ 1,963,546 Investment Securities Held-to-Maturity: Due in one year or less $ 89,359 $ 89,149 Due after one year through five years 237,113 233,022 Due after five years through ten years 152,299 148,185 Due after ten years 198,322 192,550 Total $ 677,093 $ 662,906
Summary of continuous unrealized loss position of securities	The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at December 31, 2017 and 2016 , aggregated by category and length of time that individual securities have been in a continuous unrealized loss position. As of December 31, 2017 , the Corporation's securities portfolio consisted of 2,329 securities, 1,518 of which were in an unrealized loss position. Less Than 12 Months 12 Months or More Total (Dollars in thousands) Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses December 31, 2017 Government sponsored agencies $ 63,818 $ 510 $ 24,621 $ 438 $ 88,439 $ 948 State and political subdivisions 437,407 12,268 349,242 10,093 786,649 22,361 Residential mortgage-backed securities 93,508 383 56,576 1,243 150,084 1,626 Collateralized mortgage obligations 713,525 7,235 73,707 1,249 787,232 8,484 Corporate bonds 71,447 1,138 47,878 454 119,325 1,592 Preferred stock and trust preferred securities — — 11,164 172 11,164 172 Total $ 1,379,705 $ 21,534 $ 563,188 $ 13,649 $ 1,942,893 $ 35,183 December 31, 2016 Government sponsored agencies $ 105,702 $ 1,707 $ 15,023 $ 361 $ 120,725 $ 2,068 State and political subdivisions 758,063 28,158 26,810 975 784,873 29,133 Residential mortgage-backed securities 244,239 3,992 — — 244,239 3,992 Collateralized mortgage obligations 279,001 3,778 14,754 225 293,755 4,003 Corporate bonds 80,536 1,401 — — 80,536 1,401 Preferred stock and trust preferred securities 10,699 80 310 190 11,009 270 Total $ 1,478,240 $ 39,116 $ 56,897 $ 1,751 $ 1,535,137 $ 40,867

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Summary of loans under portfolio	A summary of the Corporation's loans follows: (Dollars in thousands) Originated Acquired (1) Total loans December 31, 2017 Commercial loan portfolio: Commercial $ 2,407,606 $ 978,036 $ 3,385,642 Commercial real estate 2,751,425 1,749,245 4,500,670 Real estate construction and land development 498,155 76,060 574,215 Subtotal 5,657,186 2,803,341 8,460,527 Consumer loan portfolio: Residential mortgage 1,967,857 1,284,630 3,252,487 Consumer installment 1,510,540 102,468 1,613,008 Home equity 611,846 217,399 829,245 Subtotal 4,090,243 1,604,497 5,694,740 Total loans (2) $ 9,747,429 $ 4,407,838 $ 14,155,267 December 31, 2016 Commercial loan portfolio: Commercial $ 1,901,526 $ 1,315,774 $ 3,217,300 Commercial real estate 1,921,799 2,051,341 3,973,140 Real estate construction and land development 281,724 122,048 403,772 Subtotal 4,105,049 3,489,163 7,594,212 Consumer loan portfolio: Residential mortgage 1,475,342 1,611,132 3,086,474 Consumer installment 1,282,588 151,296 1,433,884 Home equity 595,422 280,787 876,209 Subtotal 3,353,352 2,043,215 5,396,567 Total loans (2) $ 7,458,401 $ 5,532,378 $ 12,990,779 (1) Acquired loans are accounted for under ASC 310-30. (2) Reported net of deferred costs totaling $26.1 million and $14.8 million at December 31, 2017 and 2016 , respectively.
Schedule of activity for accretable yield	Activity for the accretable yield is as follows: (Dollars in thousands) Talmer Lake Michigan Monarch North-western OAK Total Year Ended December 31, 2017 Balance at beginning of period $ 798,210 $ 121,416 $ 27,182 $ 69,847 $ 23,316 $ 1,039,971 Accretion recognized in interest income (175,678 ) (29,077 ) (4,533 ) (20,318 ) (12,563 ) (242,169 ) Net reclassification (to) from nonaccretable difference (1) 108,821 2,785 (153 ) 11,285 6,357 129,095 Balance at end of period $ 731,353 $ 95,124 $ 22,496 $ 60,814 $ 17,110 $ 926,897 Year Ended December 31, 2016 Balance at beginning of period $ — $ 152,999 $ 34,558 $ 82,623 $ 28,077 $ 298,257 Addition attributable to acquisitions 862,127 — — — — 862,127 Additions (reductions) (1) — (3,552 ) (1,908 ) (6,985 ) 1,091 (11,354 ) Accretion recognized in interest income (63,917 ) (33,031 ) (5,468 ) (15,791 ) (13,352 ) (131,559 ) Net reclassification (to) from nonaccretable difference (1) — 5,000 — 10,000 7,500 22,500 Balance at end of period $ 798,210 $ 121,416 $ 27,182 $ 69,847 $ 23,316 $ 1,039,971 Year Ended December 31, 2015 Balance at beginning of period $ — $ — $ — $ 104,675 $ 33,286 $ 137,961 Addition attributable to acquisitions — 190,246 37,914 — — 228,160 Additions (reductions) (1) — (12,991 ) 1,336 (3,396 ) 6,601 (8,450 ) Accretion recognized in interest income — (24,256 ) (4,692 ) (18,656 ) (11,810 ) (59,414 ) Net reclassification (to) from nonaccretable difference (1) — — — — — — Balance at end of period $ — $ 152,999 $ 34,558 $ 82,623 $ 28,077 $ 298,257 (1) The net reclassification results from changes in expected cash flows of the acquired loans which may include increases in the amount of contractual principal and interest expected to be collected due to improvement in credit quality, increases in balances outstanding from advances, renewals, extensions and interest rates; as well as reductions in contractual principal and interest expected to be collected due to credit deterioration, payoffs, and decreases in interest rates.
Recorded investment of loans in the commercial loan portfolio by risk rating categories	The following schedule presents the recorded investment of loans in the commercial loan portfolio by credit risk categories at December 31, 2017 and 2016 : (Dollars in thousands) Pass Special Mention Substandard Doubtful Total December 31, 2017 Originated Portfolio: Commercial $ 2,316,464 $ 41,059 $ 50,083 $ — $ 2,407,606 Commercial real estate 2,677,579 24,204 49,642 — 2,751,425 Real estate construction and land development 494,528 837 2,790 — 498,155 Subtotal 5,488,571 66,100 102,515 — 5,657,186 Acquired Portfolio: Commercial 873,861 68,418 35,539 218 978,036 Commercial real estate 1,603,685 67,970 76,803 787 1,749,245 Real estate construction and land development 72,346 2,218 1,496 — 76,060 Subtotal 2,549,892 138,606 113,838 1,005 2,803,341 Total $ 8,038,463 $ 204,706 $ 216,353 $ 1,005 $ 8,460,527 December 31, 2016 Originated Portfolio: Commercial $ 1,803,750 $ 44,809 $ 51,898 $ 1,069 $ 1,901,526 Commercial real estate 1,849,315 36,981 35,502 1 1,921,799 Real estate construction and land development 280,968 157 599 — 281,724 Subtotal 3,934,033 81,947 87,999 1,070 4,105,049 Acquired Portfolio: Commercial 1,218,848 46,643 50,283 — 1,315,774 Commercial real estate 1,897,011 61,441 92,636 253 2,051,341 Real estate construction and land development 117,505 1,982 2,561 — 122,048 Subtotal 3,233,364 110,066 145,480 253 3,489,163 Total $ 7,167,397 $ 192,013 $ 233,479 $ 1,323 $ 7,594,212
Recorded investment of loans in the consumer loan portfolio based on the credit risk profile of loans in a performing and nonperforming status	The following schedule presents the recorded investment of loans in the consumer loan portfolio based on loans in a performing status and loans in a nonperforming status at December 31, 2017 and 2016 : (Dollars in thousands) Residential mortgage Consumer installment Home equity Total consumer December 31, 2017 Originated Portfolio: Performing $ 1,959,222 $ 1,509,698 $ 607,541 $ 4,076,461 Nonperforming 8,635 842 4,305 13,782 Subtotal 1,967,857 1,510,540 611,846 4,090,243 Acquired Loans 1,284,630 102,468 217,399 1,604,497 Total $ 3,252,487 $ 1,613,008 $ 829,245 $ 5,694,740 December 31, 2016 Originated Portfolio: Performing $ 1,468,373 $ 1,281,709 $ 592,071 $ 3,342,153 Nonperforming 6,969 879 3,351 11,199 Subtotal 1,475,342 1,282,588 595,422 3,353,352 Acquired Loans 1,611,132 151,296 280,787 2,043,215 Total $ 3,086,474 $ 1,433,884 $ 876,209 $ 5,396,567
Summary of nonperforming loans	A summary of nonperforming assets follows: December 31, (Dollars in thousands) 2017 2016 Nonperforming assets Nonaccrual loans: Commercial $ 19,691 $ 13,178 Commercial real estate 29,545 19,877 Real estate construction and land development 77 80 Residential mortgage 8,635 6,969 Consumer installment 842 879 Home equity 4,305 3,351 Total nonaccrual loans 63,095 44,334 Other real estate owned and repossessed assets 8,807 17,187 Total nonperforming assets $ 71,902 $ 61,521 Accruing loans contractually past due 90 days or more as to interest or principal payments, excluding acquired loans accounted for under ASC 310-30 Commercial $ — $ 11 Commercial real estate 13 277 Residential mortgage — — Home equity 1,364 995 Total accruing loans contractually past due 90 days or more as to interest or principal payments, excluding acquired loans accounted for under ASC 310-30 $ 1,377 $ 1,283
Schedule representing the aging status of the recorded investment in loans by classes	Loan delinquency, excluding acquired loans accounted for under ASC 310-30, was as follows: (Dollars in thousands) 30-59 days past due 60-89 days past due 90 days or more past due Total past due Current Total loans 90 days or more past due and still accruing December 31, 2017 Originated Portfolio: Commercial $ 13,906 $ 3,766 $ 9,494 $ 27,166 $ 2,380,440 $ 2,407,606 $ — Commercial real estate 9,380 1,562 5,873 16,815 2,734,610 2,751,425 13 Real estate construction and land development — — — — 498,155 498,155 — Residential mortgage 2,795 1,415 858 5,068 1,962,789 1,967,857 — Consumer installment 3,324 442 226 3,992 1,506,548 1,510,540 — Home equity 2,319 1,301 2,196 5,816 606,030 611,846 1,364 Total $ 31,724 $ 8,486 $ 18,647 $ 58,857 $ 9,688,572 $ 9,747,429 $ 1,377 December 31, 2016 Originated Portfolio: Commercial $ 10,421 $ 4,842 $ 3,641 $ 18,904 $ 1,882,622 $ 1,901,526 $ 11 Commercial real estate 6,551 1,589 5,165 13,305 1,908,494 1,921,799 277 Real estate construction and land development 2,721 499 — 3,220 278,504 281,724 — Residential mortgage 3,147 62 1,752 4,961 1,470,381 1,475,342 — Consumer installment 3,991 675 238 4,904 1,277,684 1,282,588 — Home equity 3,097 893 2,349 6,339 589,083 595,422 995 Total $ 29,928 $ 8,560 $ 13,145 $ 51,633 $ 7,406,768 $ 7,458,401 $ 1,283
Schedule of Impaired loans by classes	The following schedules present impaired loans by classes of loans at December 31, 2017 and December 31, 2016 : (Dollars in thousands) Recorded investment Unpaid principal balance Related valuation allowance December 31, 2017 Impaired loans with a valuation allowance: Commercial $ 28,897 $ 31,655 $ 2,296 Commercial real estate 28,003 34,580 3,227 Real estate construction and land development 313 313 14 Residential mortgage 15,872 15,872 1,487 Consumer installment 966 966 120 Home equity 4,570 4,570 858 Subtotal 78,621 87,956 8,002 Impaired loans with no related valuation allowance: Commercial 8,504 9,291 — Commercial real estate 18,080 19,861 — Real estate construction and land development — — — Residential mortgage 4,902 4,902 — Consumer installment — — — Home equity 1,770 1,770 — Subtotal 33,256 35,824 — Total impaired loans: Commercial 37,401 40,946 2,296 Commercial real estate 46,083 54,441 3,227 Real estate construction and land development 313 313 14 Residential mortgage 20,774 20,774 1,487 Consumer installment 966 966 120 Home equity 6,340 6,340 858 Total $ 111,877 $ 123,780 $ 8,002 (Dollars in thousands) Recorded investment Unpaid principal balance Related valuation allowance December 31, 2016 Impaired loans with a valuation allowance: Commercial $ 28,925 $ 33,209 $ 3,128 Commercial real estate 21,318 27,558 2,102 Real estate construction and land development 177 177 4 Residential mortgage 20,864 20,864 3,528 Consumer installment 879 879 240 Home equity 2,577 2,577 390 Subtotal 74,740 85,264 9,392 Impaired loans with no related valuation allowance: Commercial 7,435 11,153 — Commercial real estate 20,588 23,535 — Real estate construction and land development 80 80 — Residential mortgage 3,252 3,252 — Consumer installment — — — Home equity 774 774 — Subtotal 32,129 38,794 — Total impaired loans: Commercial 36,360 44,362 3,128 Commercial real estate 41,906 51,093 2,102 Real estate construction and land development 257 257 4 Residential mortgage 24,116 24,116 3,528 Consumer installment 879 879 240 Home equity 3,351 3,351 390 Total $ 106,869 $ 124,058 $ 9,392 The following schedule presents additional information regarding impaired loans by classes of loans segregated by those requiring a valuation allowance and those not requiring a valuation allowance at December 31, 2017 , 2016 and 2015 and the respective interest income amounts recognized: For the years ended December 31, 2017 2016 2015 (Dollars in thousands) Average annual recorded investment Interest income recognized while on impaired status Average annual recorded investment Interest income recognized while on impaired status Average annual recorded investment Interest income recognized while on impaired status Impaired loans with a valuation allowance: Commercial $ 25,099 $ 939 $ 7,829 $ — $ 9,511 $ — Commercial real estate 19,983 677 5,658 — 2,918 — Real estate construction and land development 175 10 19 — — — Residential mortgage 16,390 538 23,958 1,285 20,661 1,312 Consumer installment 744 4 359 — — — Home equity 4,201 82 1,759 — — — Subtotal 66,592 2,250 39,582 1,285 33,090 1,312 Impaired loans with no related valuation allowance: Commercial 10,196 28 29,559 1,343 27,778 1,005 Commercial real estate 24,658 245 41,646 1,236 50,079 1,547 Real estate construction and land development 78 — 585 22 889 25 Residential mortgage 4,622 38 1,519 — 6,027 — Consumer installment 205 — — — 448 — Home equity 1,392 14 555 — 1,872 — Subtotal 41,151 325 73,864 2,601 87,093 2,577 Total impaired loans: Commercial 35,295 967 37,388 1,343 37,289 1,005 Commercial real estate 44,641 922 47,304 1,236 52,997 1,547 Real estate construction and land development 253 10 604 22 889 25 Residential mortgage 21,012 576 25,477 1,285 26,688 1,312 Consumer installment 949 4 359 — 448 — Home equity 5,593 96 2,314 — 1,872 — Total $ 107,743 $ 2,575 $ 113,446 $ 3,886 $ 120,183 $ 3,889
Schedule providing information on performing and nonperforming TDRs	The following tables present the recorded investment of loans modified into TDRs during the years ended December 31, 2017 , 2016 and 2015 by type of concession granted. In cases where more than one type of concession was granted, the loans were categorized based on the most significant concession. Concession type (Dollars in thousands) Principal Principal A/B Note Restructure (1) Interest Forbearance Total Pre- modification recorded investment Post- modification recorded investment For the year ended December 31, 2017 Commercial loan portfolio: Commercial $ 2,308 $ — $ — $ 1,827 $ 2,176 36 $ 6,416 $ 6,311 Commercial real estate 706 — — 338 953 16 2,097 1,997 Real estate construction and land development 35 — — — — 1 36 35 Subtotal 3,049 — — 2,165 3,129 53 8,549 8,343 Consumer loan portfolio: Residential mortgage 297 — — 383 — 11 763 680 Consumer installment 118 37 — 37 — 34 208 192 Home equity 389 — — 52 — 14 537 441 Subtotal 804 37 — 472 — 59 1,508 1,313 Total loans $ 3,853 $ 37 $ — $ 2,637 $ 3,129 112 $ 10,057 $ 9,656 For the year ended December 31, 2016 Commercial loan portfolio: Commercial $ 11,533 $ 1,527 $ 43 $ — $ 1,750 54 $ 14,853 $ 14,853 Commercial real estate 2,993 1,866 — — — 16 4,859 4,859 Subtotal 14,526 3,393 43 — 1,750 70 19,712 19,712 Consumer loan portfolio: Residential mortgage 477 — — — — 4 477 477 Consumer installment 87 — — — — 14 87 87 Home equity 179 — — 364 — 10 543 543 Subtotal 743 — — 364 — 28 1,107 1,107 Total loans $ 15,269 $ 3,393 $ 43 $ 364 $ 1,750 98 $ 20,819 $ 20,819 For the year ended December 31, 2015 Commercial loan portfolio: Commercial $ 6,031 $ — $ — $ 117 $ 5,298 53 $ 11,446 $ 11,446 Commercial real estate 5,904 450 — 102 740 21 7,196 7,196 Real estate construction and land development 705 — — — — 3 705 705 Subtotal 12,640 450 — 219 6,038 77 19,347 19,347 Consumer loan portfolio: Residential mortgage 1,246 — — 635 — 20 1,881 1,881 Consumer installment 210 — — — — 19 210 210 Home equity 1,110 — — 46 — 26 1,158 1,156 Subtotal 2,566 — — 681 — 65 3,249 3,247 Total loans $ 15,206 $ 450 $ — $ 900 $ 6,038 142 $ 22,596 $ 22,594 (1) Loan restructurings whereby the original loan is restructured into two notes: an "A" note, which generally reflects the portion of the modified loans which is expected to be collected: and a "B" note, which is fully charged off.
Schedule of Corporation's TDRs	The following schedule presents the Corporation's TDRs at December 31, 2017 and 2016 : (Dollars in thousands) Accruing TDRs Nonaccrual TDRs Total December 31, 2017 Commercial loan portfolio $ 34,484 $ 24,358 $ 58,842 Consumer loan portfolio 14,298 4,748 19,046 Total $ 48,782 $ 29,106 $ 77,888 December 31, 2016 Commercial loan portfolio $ 45,388 $ 25,397 $ 70,785 Consumer loan portfolio 17,147 5,134 22,281 Total $ 62,535 $ 30,531 $ 93,066
Troubled debt restructurings on financing receivables with defaults payment	The following schedule includes TDRs for which there was a payment default during the years ended December 31, 2017 , 2016 and 2015 , whereby the borrower was past due with respect to principal and/or interest for 90 days or more, and the loan became a TDR during the twelve-month period prior to the default: For the years ended December 31, 2017 2016 2015 Number of loans Principal balance at year end Number of loans Principal balance at year end Number of loans Principal balance at year end (Dollars in thousands) Commercial loan portfolio: Commercial 5 $ 1,617 — $ — 1 $ 1,206 Commercial real estate — — 2 1,721 5 1,016 Subtotal - commercial loan portfolio 5 1,617 2 1,721 6 2,222 Consumer loan portfolio (residential mortgage) 17 434 14 259 3 65 Total 22 $ 2,051 16 $ 1,980 9 $ 2,287
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	The following schedule presents by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2017 and 2016 by impairment evaluation method. (Dollars in thousands) Commercial Consumer Total Allowance for loan losses balance at December 31, 2017 attributable to: Loans individually evaluated for impairment $ 5,537 $ 2,465 $ 8,002 Loans collectively evaluated for impairment 60,596 23,289 83,885 Loans accounted for under ASC 310-30 — — — Total $ 66,133 $ 25,754 $ 91,887 Recorded investment (loan balance) at December 31, 2017: Loans individually evaluated for impairment $ 83,797 $ 28,080 $ 111,877 Loans collectively evaluated for impairment 5,573,389 4,062,163 9,635,552 Loans accounted for under ASC 310-30 2,803,341 1,604,497 4,407,838 Total $ 8,460,527 $ 5,694,740 $ 14,155,267 Allowance for loan losses balance at December 31, 2016 attributable to: Loans individually evaluated for impairment $ 5,234 $ 4,158 $ 9,392 Loans collectively evaluated for impairment 45,967 22,909 68,876 Loans accounted for under ASC 310-30 — — — Total $ 51,201 $ 27,067 $ 78,268 Recorded investment (loan balance) at December 31, 2016: Loans individually evaluated for impairment $ 78,523 $ 28,346 $ 106,869 Loans collectively evaluated for impairment 4,026,526 3,325,006 7,351,532 Loans accounted for under ASC 310-30 3,489,163 2,043,215 5,532,378 Total $ 7,594,212 $ 5,396,567 $ 12,990,779 The following schedule presents, by loan portfolio segment, the changes in the allowance for the originated loan portfolio for the years ended December 31, 2017 , 2016 and 2015 . (Dollars in thousands) Commercial loan portfolio Consumer loan portfolio Unallocated Total Originated Loan Portfolio Changes in allowance for loan losses for the year ended December 31, 2017: Beginning balance $ 51,201 $ 27,067 $ — $ 78,268 Provision for loan losses 19,007 4,293 — 23,300 Charge-offs (8,570 ) (8,297 ) — (16,867 ) Recoveries 4,495 2,691 — 7,186 Ending balance $ 66,133 $ 25,754 $ — $ 91,887 Changes in allowance for loan losses for the year ended December 31, 2016: Beginning balance $ 47,234 $ 26,094 $ — $ 73,328 Provision (benefit) for loan losses 9,788 5,087 — 14,875 Charge-offs (8,906 ) (6,396 ) — (15,302 ) Recoveries 3,085 2,282 — 5,367 Ending balance $ 51,201 $ 27,067 $ — $ 78,268 Changes in allowance for loan losses for the year ended December 31, 2015: Beginning balance $ 44,156 $ 28,803 $ 2,724 $ 75,683 Provision (benefit) for loan losses 7,275 1,949 (2,724 ) 6,500 Charge-offs (6,385 ) (7,116 ) — (13,501 ) Recoveries 2,188 2,458 — 4,646 Ending balance $ 47,234 $ 26,094 $ — $ 73,328

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of premises and equipment	The following table summarizes premises and equipment: December 31, (Dollars in thousands) 2017 2016 Land and land improvements $ 31,427 $ 36,185 Buildings 130,028 144,155 Furniture and equipment 100,932 91,963 Total 262,387 272,303 Less accumulated depreciation (135,491 ) (127,291 ) Premises and equipment, net $ 126,896 $ 145,012

Other Real Estate Owned and R39

Other Real Estate Owned and Repossessed Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Other Real Estate [Abstract]
Tabular disclosure of the changes in non-covered and covered other real estate on properties owned	Changes in other real estate owned and repossessed assets, included in interest receivable and other assets on the Consolidated Statements of Financial Position, were as follows: (Dollars in thousands) Other real estate Repossessed Balance at January 1, 2015 $ 13,953 $ 252 Additions due to acquisitions 440 — Other additions (1) 6,957 2,372 Net payments received (45 ) (22 ) Disposals (10,168 ) (2,383 ) Write-downs (1,421 ) — Balance at December 31, 2015 $ 9,716 $ 219 Additions due to acquisitions 13,227 313 Other additions (1) 9,938 3,032 Net payments received (1,560 ) (763 ) Disposals (13,873 ) (2,426 ) Write-downs (636 ) — Balance at December 31, 2016 $ 16,812 $ 375 Other additions (1) 6,905 4,641 Net payments received (1,064 ) — Disposals (12,831 ) (4,391 ) Write-downs (1,640 ) — Balance at December 31, 2017 $ 8,182 $ 625 (1) Includes loans transferred to other real estate owned and other repossessed assets.
Schedule of income and expenses related to other real estate owned	Income and expenses related to other real estate owned and repossessed assets, recorded as a component of “Other expense” in the Consolidated Statements of Income, were as follows: (Dollars in thousands) Other real estate owned Repossessed assets For the year ended December 31, 2017 Net gain (loss) on sale $ 3,038 $ (381 ) Write-downs (1,640 ) — Net operating expenses (1,981 ) (41 ) Total $ (583 ) $ (422 ) For the year ended December 31, 2016 Net gain (loss) on sale $ 5,325 $ 523 Write-downs (636 ) — Net operating expenses (740 ) (60 ) Total $ 3,949 $ 463 For the year ended December 31, 2015 Net gain (loss) on sale $ 4,128 $ (26 ) Write-downs (1,421 ) — Net operating expenses (1,604 ) (19 ) Total $ 1,103 $ (45 )

Loan Servicing Rights (Tables)

Loan Servicing Rights (Tables)	12 Months Ended
	Dec. 31, 2017
Transfers and Servicing [Abstract]
Schedule of activity for loan servicing rights and the related fair value changes	The following table represents the activity for LSRs and the related fair value changes: (Dollars in thousands) Commercial Real Estate Mortgage Total For the year ended December 31, 2017 Fair value, beginning of period $ 344 $ 47,741 $ 48,085 Transfers in based on new accounting policy election — 15,891 15,891 Additions from loans sold with servicing retained 188 8,557 8,745 Changes in fair value due to: Reductions from pay-offs, pay downs and run-off (105 ) (2,400 ) (2,505 ) Changes in estimates of fair value (1) — (6,375 ) (6,375 ) Fair value, end of period $ 427 $ 63,414 $ 63,841 Principal balance of loans serviced $ 40,316 $ 7,068,431 $ 7,108,747 For the year ended December 31, 2016 Fair value, beginning of period $ — $ — $ — Acquired in Talmer Bancorp, Inc. merger 365 42,097 42,462 Additions from loans sold with servicing retained — 1,030 1,030 Changes in fair value due to: Reductions from pay-offs, pay downs and run-off (17 ) (502 ) (519 ) Changes in estimates of fair value (1) (4 ) 5,116 5,112 Fair value, end of period $ 344 $ 47,741 $ 48,085 Principal balance of loans serviced under the fair value measurement method $ 64,756 $ 5,235,415 $ 5,300,171 (1) Represents estimated LSR value change resulting primarily from market-driven changes in interest rates and prepayments. Included in "Net gain on sale of loans and other mortgage banking revenue" in the Consolidated Statements of Income.
Net carrying value, fair value of mortgage servicing rights and loans Corporation servicing for others	The following shows the net carrying value and fair value of LSRs and the total loans that the Corporation serviced for others accounted for at the lower of cost or fair value for the years ended December 31, 2016 and 2015: Years Ended December 31, (Dollars in thousands) 2016 2015 Net carrying value of LSRs $ 10,230 $ 11,122 Fair value of LSRs $ 15,891 $ 15,542 Valuation allowance $ 8 $ — Loans serviced for others that have servicing rights capitalized $ 2,074,057 $ 2,082,899
Activity for capitalized loan servicing rights	Activity for LSRs accounted for at the lower of cost or fair value and the related valuation allowance for the years ended December 31, 2016 and 2015 are as follows: Years Ended December 31, (Dollars in thousands) 2016 2015 Balance at beginning of period $ 11,122 $ 12,217 Acquired through acquisitions — 1,284 Additions 3,303 1,476 Amortization (4,187 ) (4,055 ) Change in valuation allowance (8 ) 200 Balance at end of period $ 10,230 $ 11,122
Schedule of assumptions included in loan servicing rights	Expected and actual loan prepayment speeds are the most significant factors driving the fair value of loan servicing rights. The following table presents assumptions utilized in determining the fair value of loan servicing rights as of December 31, 2017 and 2016 . Mortgage As of December 31, 2017 Prepayment speed 0.00 - 38.8% Weighted average ("WA") discount rate 10.1 % Cost to service/per year $ 66 WA Ancillary income/per year $ 31 WA float range 1.6 % As of December 31, 2016 Prepayment speed 0.00 - 99.8% WA discount rate 10.1 % Cost to service/per year $65-$90 Ancillary income/per year $ 28 WA float range 1.0 %

Derivative Instruments and Ba41

Derivative Instruments and Balance Sheet Offsetting (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule reflecting the amount and fair value of risk management derivatives and mortgage banking and customer initiated derivatives	The following table presents the notional amount and fair value of the Corporation’s derivative instruments held or issued in connection with customer-initiated and mortgage banking activities. December 31, 2017 2016 Fair Value Fair Value (Dollars in thousands) Notional Amount (1) Gross Derivative Assets (2) Gross Derivative Liabilities (2) Notional Amount (1) Gross Derivative Assets (2) Gross Derivative Liabilities (2) Risk management purposes: Derivatives designated as hedging instruments: Interest rate swaps $ 620,000 $ 5,899 $ — $ — $ — $ — Total risk management purposes 620,000 5,899 — — — — Customer-initiated and mortgage banking derivatives: Customer-initiated derivatives 1,365,119 9,376 10,139 600,598 4,406 4,141 Foreign exchange forwards (3) — — — — — — Forward contracts related to mortgage loans to be delivered for sale 115,996 — 34 140,155 635 — Interest rate lock commitments 71,003 1,222 — 76,034 956 — Power Equity CD 38,807 2,184 2,184 36,807 2,218 2,218 Total customer-initiated and mortgage banking derivatives 1,590,925 12,782 12,357 853,594 8,215 6,359 Total gross derivatives $ 2,210,925 $ 18,681 $ 12,357 $ 853,594 $ 8,215 $ 6,359 (1) Notional or contract amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the Consolidated Statements of Financial Position. (2) Derivative assets are included within "Interest receivable and other assets" and derivative liabilities are included within "Interest Payable and other liabilities" on the Consolidated Statements of Financial Position. Included in the fair value of the derivative assets are credit valuation adjustments for counterparty credit risk totaling $809 thousand at December 31, 2017 and $99 thousand at December 31, 2016 . (3) The foreign exchange forwards that were entered into during the year ended December 31, 2017 had matured as of December 31, 2017 .
Schedule reflecting the net gains (losses) relating to derivative instruments related to the changes in fair value	The following table presents the net gains (losses) related to derivative instruments reflecting the changes in fair value. For the years ended December 31, (Dollars in thousands) Location of Gain (Loss) 2017 2016 2015 Forward contracts related to mortgage loans to be delivered for sale Net gain (loss) on sale of loans and other mortgage banking revenue $ (669 ) $ 692 $ 193 Interest rate lock commitments Net gain (loss) on sale of loans and other mortgage banking revenue 266 (1,356 ) (132 ) Customer-initiated derivatives Other noninterest income (1,028 ) 581 — Total gain (loss) recognized in income $ (1,431 ) $ (83 ) $ 61 The following table presents the net gains (losses) recorded in accumulated other comprehensive income and the Consolidated Statements of Income relating to interest rate swaps designated as cash flow hedges for the year ended December 31, 2017 . The Corporation first began entering into interest rate swaps designated as cash flow hedges during the year ended December 31, 2017. (Dollars in thousands) Amount of gain (loss) recognized in other comprehensive income (Effective portion) Amount of gain (loss) reclassified from other comprehensive income to interest income or expense (Effective portion) Amount of gain (loss) recognized in other noninterest income (Ineffective portion) Year Ended December 31, 2017 Interest rate swaps designated as cash flow hedges $ 4,263 $ (1,633 ) $ (3 )
Schedule of the Company's financial instruments eligible for offset, offsetting assets	The tables below present information about the Corporation’s financial instruments that are eligible for offset. Gross amounts not offset in the (Dollars in thousands) Gross Gross amounts Net amounts Financial Collateral Net December 31, 2017 Offsetting derivative assets Derivative assets $ 15,228 $ — $ 15,228 $ — $ — $ 15,228 Offsetting derivative liabilities Derivative liabilities 10,139 — 10,139 — 1,081 9,058 December 31, 2016 Offsetting derivative assets Derivative assets $ 4,405 $ — $ 4,405 $ — $ — $ 4,405 Offsetting derivative liabilities Derivative liabilities 4,141 — 4,141 — 2,550 1,591
Schedule of the Company's financial instruments eligible for offset, offsetting liabilities	The tables below present information about the Corporation’s financial instruments that are eligible for offset. Gross amounts not offset in the (Dollars in thousands) Gross Gross amounts Net amounts Financial Collateral Net December 31, 2017 Offsetting derivative assets Derivative assets $ 15,228 $ — $ 15,228 $ — $ — $ 15,228 Offsetting derivative liabilities Derivative liabilities 10,139 — 10,139 — 1,081 9,058 December 31, 2016 Offsetting derivative assets Derivative assets $ 4,405 $ — $ 4,405 $ — $ — $ 4,405 Offsetting derivative liabilities Derivative liabilities 4,141 — 4,141 — 2,550 1,591

Other Intangible Assets (Tables

Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Net carrying value of other intangible assets	The following table shows the net carrying value of the Corporation's other intangible assets. December 31, (Dollars in thousands) 2017 2016 Core deposit intangible assets $ 34,259 $ 40,211 Non-compete intangible assets 12 — Total other intangible assets $ 34,271 $ 40,211
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	The following table sets forth the carrying amount and accumulated amortization of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions: December 31, (Dollars in thousands) 2017 2016 Gross carrying amount $ 59,143 $ 59,143 Accumulated amortization 24,884 18,932 Net carrying amount $ 34,259 $ 40,211
Estimated future amortization expense on CDIs	The estimated future amortization expense on core deposit intangible assets for the next five years is as follows: (Dollars in thousands) Estimated amortization expense 2018 $ 5,703 2019 5,441 2020 4,850 2021 4,471 2022 4,218

Commitments, Contingencies an43

Commitments, Contingencies and Guarantees (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of activity related to liability recorded in connection with representation and warranties	A summary of the reserve for representations and warranties of the Corporation is as follows: For the years ended December 31, (Dollars in thousands) 2017 2016 2015 Reserve balance at beginning of period $ 6,459 $ 4,048 $ 3,000 Addition of fair value of representations and warranties due to mergers and acquisitions — 3,100 1,712 Reserve reduction (1,095 ) (580 ) — Charge-offs (15 ) (109 ) (664 ) Ending reserve balance $ 5,349 $ 6,459 $ 4,048 Reserve balance: Liability for specific claims 531 730 — General allowance 4,818 5,729 4,048 Total reserve balance $ 5,349 $ 6,459 $ 4,048
Schedule of future minimum lease payments for operating leases	Future minimum lease payments for operating leases and other noncancelable contractual obligations are as follows: (Dollars in thousands) Future Minimum Lease Payments (1) Years ending December 31, 2018 $ 22,973 2019 21,487 2020 18,808 2021 16,794 2022 20,112 Thereafter 33,775 Total $ 133,949 (1) Future minimum lease payments are reduced by $0.9 million related to sublease income to be received within the next five years.

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Schedule of Deposits	A summary of deposits follows: December 31, (Dollars in thousands) 2017 2016 Noninterest-bearing demand $ 3,725,779 $ 3,341,520 Savings 1,697,762 1,662,115 Interest-bearing demand 2,724,415 2,825,801 Money market accounts 1,957,909 2,033,319 Brokered deposits 453,227 226,429 Other time deposits 3,083,711 2,783,938 Total deposits $ 13,642,803 $ 12,873,122 At December 31, 2017 , the scheduled maturities of time deposits for the next five years were as follows: (Dollars in thousands) 2018 $ 2,168,858 2019 646,514 2020 183,101 2021 134,806 2022 81,169 Thereafter 2,759 Total $ 3,217,207

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Short- and Long-term Borrowings	A summary of the Corporation's short- and long-term borrowings follows: December 31, 2017 2016 (Dollars in thousands) Amount Weighted Average Rate (1) Amount Weighted Average Rate (1) Securities sold under agreements to repurchase with customers: Securities sold under agreements to repurchase with customers $ 415,236 0.44 % $ 343,047 0.16 % Short-term borrowings: FHLB advances: 1.25% - 1.50% fixed-rate notes 2,000,000 1.39 825,000 0.65 Long-term borrowings: FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020 (2) 337,204 1.26 438,538 1.24 Securities sold under agreements to repurchase (3) — — 19,144 3.17 Line-of-credit: floating-rate based on one-month LIBOR plus 1.75% 19,963 3.10 124,625 2.52 Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 (4) 11,425 3.69 11,285 3.14 Subordinated debt obligations: floating-rate based on three-month LIBOR plus 3.25% due in 2032 (5) 4,290 4.59 4,255 4.25 Total long-term borrowings 372,882 1.47 597,847 1.63 Total short-term and long-term borrowings $ 2,788,118 1.26 % $ 1,765,894 0.89 % (1) Weighted average rate presented is the contractual rate which excludes premiums and discounts related to purchase accounting. (2) The December 31, 2017 balance includes advances payable of $337.0 million and purchase accounting premiums of $0.2 million . The December 31, 2016 balance includes advances payable of $437.8 million and purchase accounting premiums of $0.7 million . (3) The December 31, 2016 balance includes advance payable of $19.0 million and purchase accounting premiums of $0.1 million . (4) The December 31, 2017 balance includes advances payable of $15.0 million and purchase accounting discounts of $3.6 million . The December 31, 2016 balance includes advance payable of $15.0 million and purchase accounting premiums of $3.7 million . (5) The December 31, 2017 balance includes advances payable of $5.0 million and purchase accounting discounts of $0.7 million . The December 31, 2016 balance includes advance payable of $5.0 million and purchase accounting premiums of $0.7 million .
Long-term Debt by Maturity	At December 31, 2017 , the contractual principal payments due and the amortization/accretion of purchase accounting adjustments for the remaining maturities of long-term debt over the next five years and thereafter are as follows: (Dollars in thousands) Long-term Debt by Maturity Years Ending December 31, 2018 $ 147,065 2019 100,058 2020 110,044 2021 — 2022 — Thereafter 15,715 Total $ 372,882

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for Federal Income Taxes Components	The current and deferred components of the provision for income taxes were as follows: Years Ended December 31, (Dollars in thousands) 2017 2016 2015 Current income tax expense (benefit) Federal $ 14,665 $ 19,144 $ 31,300 State 20 (423 ) — Total current income tax expense 14,685 18,721 31,300 Deferred expense (benefit) Federal 92,636 23,649 5,700 State 548 442 — Total deferred income tax expense (benefit) 93,184 24,091 5,700 Change in valuation allowance (1,089 ) (706 ) — Income tax provision $ 106,780 $ 42,106 $ 37,000
Schedule of Federal Effective Income Tax Rate Reconciliation	A reconciliation of expected income tax expense at the federal statutory income tax rate and the amounts recorded in the Consolidated Financial Statements were as follows: Years Ended December 31, 2017 2016 2015 (Dollars in thousands) Amount Rate Amount Rate Amount Rate Tax at statutory rate $ 89,706 35.0 % $ 52,548 35.0 % $ 43,341 35.0 % Changes resulting from: Tax-exempt interest income (9,001 ) (3.5 ) (5,320 ) (3.5 ) (3,943 ) (3.2 ) State taxes, net of federal benefit 369 0.1 13 — — — Change in valuation allowance (1,089 ) (0.4 ) (706 ) (0.5 ) — — Bank-owned life insurance adjustments (1,696 ) (0.7 ) (832 ) (0.6 ) (124 ) (0.1 ) Director plan change in control — — (508 ) (0.3 ) — — Income tax credits, net (11,449 ) (4.4 ) (2,454 ) (1.6 ) (2,557 ) (2.1 ) Nondeductible transaction expenses 156 0.1 2,100 1.4 411 0.3 Tax benefits in excess of compensation costs on share-based payments (1) (5,886 ) (2.3 ) (2,240 ) (1.5 ) — — Impact of the Tax Cuts and Jobs Act (2) 46,660 18.2 — — — — Other, net (990 ) (0.4 ) (495 ) (0.4 ) (128 ) — Income tax expense $ 106,780 41.7 % $ 42,106 28.0 % $ 37,000 29.9 % (1) The years ended December 31, 2017 and 2016 reflect the adoption of ASU 2016-09, as of January 1, 2016, which results in excess tax benefits recognized within "Income tax expense" rather than previously recognized directly into equity with "Additional paid-in-capital." Refer to Note 1, Summary of Significant Accounting Policies, for further details. (2) The year ended December 31, 2017 included the impact of the enactment of H.R.1 (the "Tax Cuts and Jobs Act"), which required a revaluation of net deferred tax assets and liabilities, see below for further details.
Schedule of Deferred Tax Assets and Liabilities	The significant components of the deferred tax assets and liabilities at December 31, 2017 and 2016 were as follows: December 31, (Dollars in thousands) 2017 2016 Deferred tax assets: Allowance for loan losses $ 20,446 $ 45,763 Acquisition-related fair value adjustments 27,607 54,704 Accrued stock-based compensation 4,082 18,891 Loss and tax credit carry forwards 57,969 76,446 Depreciation 2,954 11,270 Nonaccrual loan interest 6,155 9,465 Accrued expense 9,200 20,858 Other 9,127 15,751 Total deferred tax assets 137,540 253,148 Deferred tax liabilities: Loan servicing rights 13,446 20,450 Core deposit intangible assets 6,022 11,844 Goodwill 4,076 6,373 Prepaid expenses 7,390 4,873 Other 7,735 2,762 Total deferred tax liabilities 38,669 46,302 Net deferred tax asset before valuation allowance 98,871 206,846 Valuation allowance (1,150 ) (2,239 ) Net deferred tax asset $ 97,721 $ 204,607
Summary of the loss attributes, Section 382 limitations, and tax expiration periods	The following table is a summary of the loss attributes, Section 382 limitations, and tax expiration periods as of December 31, 2017 . From the Acquisition of: Talmer's Prior Ownership Changes (Dollars in thousands) Talmer Monarch First Place Holdings/First Place Bank Talmer West Bank First of Huron Corp./Signature Bank From 2009 Ownership change Not Limited by Section 382 Total Tax Loss and Credit Carryforwards as of 12/31/17: Years Expiring (except AMT Credits) 2032-2034 2026-2034 2027-2031 2028-2032 2029-2032 2027-2029 2036 Annual Section 382 limitation-base (1) $ 34,668 $ 673 $ 6,650 $ 3,028 $ 365 $ 145 $ — $ N/A Gross Federal Net Operating Losses — 15,047 — 47,284 649 1,740 — 64,720 Gross Capital Losses — — — — — — — — Realized Built-in Losses — — 68,356 8,936 — — — 77,292 Business Tax Credits 170 1,651 781 — — — 912 3,514 Less amounts not recorded due to Sec 382 Limitation — (1,738 ) (65 ) (3,218 ) — (145 ) — (5,166 ) Alternative Minimum Tax Credits - no expiration 12,473 106 2,115 — 303 — 10,832 25,829 Valuation Allowance — — — (585 ) — — (565 ) (1,150 ) (1) In respect to the Monarch and Talmer acquisitions, in addition to the statutory "base" Section 382 limitation, recognized built in gain increases the Section 382 limitation during the five year period beginning on the acquisition date. The Corporation estimates that the recognized built in gain will total $2.8 million and $253.2 million for the Monarch and Talmer acquisitions, respectively.

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of stock options outstanding by exercise price range	The following summarizes information about stock options outstanding and exercisable at December 31, 2017 : Options outstanding Options exercisable Range of exercise prices per share Number outstanding Weighted average exercise price per share Weighted average contractual term (in years) Number exercisable Weighted average exercise price per share Weighted average contractual term (in years) $11.09 - 12.80 32,691 $ 12.37 2.93 32,691 $ 12.37 2.93 $13.20 - 16.24 136,604 15.94 4.92 136,604 15.94 4.92 $19.97 - 21.10 49,546 20.36 2.62 49,546 20.36 2.62 $23.78 - 25.14 232,582 24.56 4.33 232,582 24.56 4.33 $29.45 - 32.81 537,893 31.68 7.62 290,534 30.72 7.15 $46.95 - 53.72 121,602 53.40 9.25 38,091 53.72 9.23 $11.09 - 53.72 1,110,918 $ 29.56 6.42 780,048 $ 25.99 5.56
Summary of activity for Corporation's stock options	A summary of activity for the Corporation's stock options as of and during the years ended December 31, 2017 , 2016 and 2015 is presented below: Non-vested stock options outstanding Stock options outstanding Number of options Weighted- average exercise price per share Weighted- average grant date fair value per share Number of options Weighted- average exercise price per share Outstanding at December 31, 2014 432,199 $ 26.75 $ 8.30 1,037,311 $ 25.90 Granted 244,165 30.18 8.40 244,165 30.18 Acquired — — — 132,883 12.93 Exercised — — — (310,985 ) 25.10 Vested (150,224 ) 25.57 7.80 — — Forfeited/expired (46,385 ) 27.99 8.50 (48,635 ) 28.18 Outstanding at December 31, 2015 479,755 $ 28.75 $ 8.49 1,054,739 $ 25.38 Granted 441,167 32.81 6.15 441,167 32.81 Acquired — — — 1,466,408 15.08 Exercised — — — (450,296 ) 20.02 Vested (454,360 ) 28.74 8.49 — — Forfeited/expired (58,623 ) 31.10 7.17 (58,623 ) 31.10 Outstanding at December 31, 2016 407,939 $ 32.81 $ 6.15 2,453,395 $ 21.41 Granted 132,414 53.43 9.94 132,414 53.43 Exercised — — — (1,427,159 ) 17.50 Vested (161,751 ) 37.73 7.07 — — Forfeited/expired (47,732 ) 37.55 7.03 (47,732 ) 37.55 Outstanding at December 31, 2017 330,870 $ 37.97 $ 7.09 1,110,918 $ 29.56 Exercisable/vested at December 31, 2017 780,048 $ 25.99
Assumptions of Black-Scholes option pricing model	The fair value of the stock options granted during the years ended December 31, 2017 , 2016 and 2015 were estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions. 2017 2016 2015 Expected dividend yield 3.31 % 3.30 % 3.50 % Risk-free interest rate 2.05 % 1.39 % 1.78 % Expected stock price volatility 26.7 % 27.9 % 39.1 % Expected life of options — in years 6.0 6.5 7.0 Weighted average fair value of options granted $9.94 $6.15 $8.40
Summary of activity for restricted stock units and awards	A summary of the activity for RSUs during the year ended December 31, 2017 is presented below: Number of units Weighted-average grant date fair value per unit Outstanding at December 31, 2016 298,357 $ 32.81 Granted 169,252 51.93 Converted into shares of common stock (75,639 ) 30.73 Forfeited/expired (11,030 ) 47.62 Outstanding at December 31, 2017 380,940 $ 41.29 The following table provides information regarding nonvested restricted stock awards: Nonvested restricted stock awards Number of awards Weighted-average acquisition-date fair value Nonvested at January 1, 2017 365,891 $ 46.23 Vested (277,821 ) 46.23 Forfeited (4,842 ) 46.23 Nonvested at December 31, 2017 83,228 $ 46.23

Retirement Plans (Tables)

Retirement Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Schedule of Changes in the Projected Benefit Obligation and Plan Assets of the Corporation’s Pension and Postretirement Plans	The following schedule sets forth the changes in the projected benefit obligation and plan assets of the Corporation's Plans: Pension Plan Postretirement Plan SERP (Dollars in thousands) 2017 2016 2017 2016 2017 2016 Projected benefit obligation: Benefit obligation at beginning of year $ 123,968 $ 119,873 $ 2,601 $ 3,247 $ 2,567 $ 2,160 Service cost 639 1,041 5 9 61 77 Interest cost 4,966 5,335 94 132 69 92 Settlement and other charges (1) — — — — — (264 ) Net actuarial loss (gain) 10,131 2,684 10 (478 ) (274 ) 536 Benefits paid (6,432 ) (4,965 ) (198 ) (309 ) — (34 ) Curtailment (11,911 ) — — — — — Benefit obligation at end of year 121,361 123,968 2,512 2,601 2,423 2,567 Fair value of plan assets: Fair value of plan assets at beginning of year 132,751 126,930 — — — — Actual return on plan assets 19,582 10,786 — — — — Employer contributions — — 198 309 — — Benefits paid (6,432 ) (4,965 ) (198 ) (309 ) — — Fair value of plan assets at end of year 145,901 132,751 — — — — Funded (unfunded) status at December 31 $ 24,540 $ 8,783 $ (2,512 ) $ (2,601 ) $ (2,423 ) $ (2,567 ) Accumulated benefit obligation $ 121,361 $ 115,418 $ 2,512 $ 2,601 $ 2,423 $ 2,567 (1) The settlement and other charges relate to the change in control as a result of the merger with Talmer as of August 31, 2016.
Schedule of Weighted-average rate assumptions of the Pension and Postretirement Plans	Weighted-average rate assumptions of the Corporation's Plans follow: Pension Plan Postretirement Plan SERP 2017 2016 2015 2017 2016 2015 2017 2016 2015 Discount rate used in determining benefit obligation — December 31 3.68 % 4.22 % 4.55 % 3.41 % 3.79 % 4.23 % 3.38 % 3.63 % 4.51 % Discount rate used in determining expense 4.22 4.55 4.15 3.79 4.23 3.75 — 4.51 4.07 Discount rate used in determining expense — prior to remeasurement 3.81 — — — — — 3.63 2.87 — Expected long-term return on Pension Plan assets 6.75 6.75 6.75 — — — — — — Rate of compensation increase used in determining benefit obligation — December 31 — 3.50 3.50 — — — — 3.50 3.50 Rate of compensation increase used in determining pension expense 3.50 3.50 3.50 — — — 3.50 3.50 3.50 Year 1 increase in cost of postretirement benefits — — — 6.5 7.0 7.5 — — —
Schedule of Net periodic Pension Cost (Income) of the Pension and Postretirement Plans	Net periodic pension cost (income) of the Corporation's Plans was as follows for the years ended December 31: Pension Plan Postretirement Plan SERP (Dollars in thousands) 2017 2016 2015 2017 2016 2015 2017 2016 2015 Service cost $ 639 $ 1,041 $ 1,021 $ 5 $ 9 $ 16 $ 61 $ 77 $ 70 Interest cost 4,966 5,335 5,242 94 132 133 69 92 85 Expected return on plan assets (8,938 ) (8,562 ) (8,645 ) — — — — — — Amortization of prior service credit — — (5 ) — 117 130 — — — Amortization of net actuarial loss (gain) 1,837 2,259 3,962 (162 ) (100 ) (1 ) 77 78 262 Curtailment 1 — — — — — — — — Settlement (1) — — — — — — 322 120 — Net cost (income) $ (1,495 ) $ 73 $ 1,575 $ (63 ) $ 158 $ 278 $ 529 $ 367 $ 417 (1) The settlement charge relates to the settlement of liabilities under the SERP for the retirement of the plan participant during the third quarter of 2017 and the change in control as a result of the merger with Talmer as of August 31, 2016.
Schedule of Estimated Future Benefit Payments Under the Pension and Postretirement Plans	The following schedule presents estimated future benefit payments for the next 10 years under the Corporation's Plans for retirees already receiving benefits and future retirees, assuming they retire and begin receiving unreduced benefits as soon as they are eligible: (Dollars in thousands) Pension Plan Postretirement Plan SERP 2018 $ 6,001 $ 230 $ 2,063 2019 6,297 230 22 2020 6,392 231 22 2021 6,657 230 22 2022 6,787 227 22 2023 - 2027 35,689 973 107 Total $ 67,823 $ 2,121 $ 2,258
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	A one percentage-point change in these rates would have the following effects: One Percentage-Point (Dollars in thousands) Increase Decrease Effect on total of service and interest cost components in 2016 $ 8 $ (8 ) Effect on postretirement benefit obligation as of December 31, 2016 196 (177 )
Schedule of Allocation of Plan Assets	The Pension Plan's asset allocation by asset category was as follows: December 31, Asset Category 2017 2016 Equity securities 68 % 69 % Debt securities 28 29 Other 4 2 Total 100 % 100 % The following schedule sets forth the fair value of the Pension Plan's assets and the level of the valuation inputs used to value those assets at December 31, 2017 and 2016 : (Dollars in thousands) Quoted Prices In Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total December 31, 2017 Cash $ 5,238 $ — $ — $ 5,238 Equity securities: U.S. large- and mid-cap stocks (1) 68,909 — — 68,909 U.S. small-cap mutual funds 5,377 — — 5,377 International large-cap mutual funds 18,341 — — 18,341 Emerging markets mutual funds 7,363 — — 7,363 Debt securities: U.S. Treasury and government sponsored agency bonds and notes — 548 — 548 Mutual funds (3) 40,046 — — 40,046 Other 79 — — 79 Total $ 145,353 $ 548 $ — $ 145,901 December 31, 2016 Cash $ 2,825 $ — $ — $ 2,825 Equity securities: U.S. large- and mid-cap stocks (1) 55,389 — — 55,389 U.S. small-cap mutual funds 5,687 — — 5,687 International large-cap mutual funds 13,701 — — 13,701 Emerging markets mutual funds 5,147 — — 5,147 Chemical Financial Corporation common stock 11,412 — — 11,412 Debt securities: U.S. Treasury and government sponsored agency bonds and notes — 806 — 806 Corporate bonds (2) — 1,503 — 1,503 Mutual funds (3) 36,220 — — 36,220 Other 61 — — 61 Total $ 130,442 $ 2,309 $ — $ 132,751 (1) Comprised of common stocks and mutual funds traded on U.S. Exchanges whose issuers had market capitalizations exceeding $3 billion . (2) Comprised of investment grade bonds of U.S. issuers from diverse industries. (3) Comprised primarily of fixed-income bonds issued by the U.S. Treasury and government sponsored agencies and bonds of U.S. and foreign issuers from diverse industries.
Schedule of Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax, Related to the Corporation’s Pension, Postretirement and Supplemental Plans	The following sets forth the changes in accumulated other comprehensive income (loss), net of tax, related to the Corporation's Pension Plan, Postretirement Plan and SERP during 2017 : (Dollars in thousands) Pension Plan Postretirement Plan SERP Total Accumulated other comprehensive income (loss) at beginning of year $ (26,123 ) $ 724 $ (495 ) $ (25,894 ) Comprehensive income (loss) adjustment: Prior service costs (credits) — — — — Net actuarial (income) loss 1,528 (112 ) 229 1,645 Curtailment 7,742 — — 7,742 Settlement (1) — — 209 209 Comprehensive income (loss) adjustment 9,270 (112 ) 438 9,596 Reclassification of certain income tax effects (2) (3,630 ) 132 (12 ) (3,510 ) Accumulated other comprehensive income (loss) at end of year $ (20,483 ) $ 744 $ (69 ) $ (19,808 ) (1) The settlement charge relates to the settlement of liabilities under the SERP for the retirement of the plan participant during the third quarter of 2017. (2) The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, see Note 1 for further information.
Schedule of Estimated Income (Loss) That Will Be Amortized From Accumulated Other Comprehensive Income (Loss) Into Net Periodic Cost	The estimated income (loss) that will be amortized from accumulated other comprehensive income (loss) into net periodic cost, net of tax, in 2018 is as follows: (Dollars in thousands) Pension Plan Postretirement Plan SERP Total Prior service (costs) credits $ — $ — $ — $ — Net gain (loss) (561 ) 113 — (448 ) Total $ (561 ) $ 113 $ — $ (448 )

Regulatory Capital and Reserv49

Regulatory Capital and Reserve Requirements (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Corporation's and Chemical Bank's actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy	The summary below compares the actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy: Actual Minimum Required for Capital Adequacy Purposes Minimum Required for Capital Adequacy Purposes Plus Capital Conservation Buffer Required to be Well Capitalized Under Prompt Corrective Action Regulations (Dollars in thousands) Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio December 31, 2017 Total Capital to Risk-Weighted Assets Corporation $ 1,614,046 11.0 % $ 1,179,076 8.0 % $ 1,363,307 9.3 % N/A N/A Chemical Bank 1,613,087 11.0 1,176,361 8.0 1,360,167 9.3 $ 1,470,451 10.0 % Tier 1 Capital to Risk-Weighted Assets Corporation 1,498,463 10.2 884,307 6.0 1,068,538 7.3 N/A N/A Chemical Bank 1,513,219 10.3 882,271 6.0 1,066,077 7.3 1,176,361 8.0 Common Equity Tier 1 Capital to Risk-Weighted Assets Corporation 1,498,463 10.2 663,230 4.5 847,461 5.8 N/A N/A Chemical Bank 1,513,219 10.3 661,703 4.5 845,509 5.8 955,793 6.5 Leverage Ratio Corporation 1,498,463 8.3 720,890 4.0 720,890 4.0 N/A N/A Chemical Bank 1,513,219 8.4 720,043 4.0 720,043 4.0 900,053 5.0 December 31, 2016 Total Capital to Risk-Weighted Assets Corporation $ 1,543,018 11.5 % $ 1,073,431 8.0 % $ 1,157,293 8.6 % N/A N/A Chemical Bank 1,608,980 12.0 1,068,560 8.0 $ 1,152,041 8.6 $ 1,335,700 10.0 % Tier 1 Capital to Risk-Weighted Assets Corporation 1,441,209 10.7 805,073 6.0 888,935 6.6 N/A N/A Chemical Bank 1,522,711 11.4 801,420 6.0 884,901 6.6 1,068,560 8.0 Common Equity Tier 1 Capital to Risk-Weighted Assets Corporation 1,441,209 10.7 603,805 4.5 687,667 5.1 N/A N/A Chemical Bank 1,522,711 11.4 601,065 4.5 684,546 5.1 868,205 6.5 Leverage Ratio Corporation 1,441,209 9.0 643,603 4.0 643,603 4.0 N/A N/A Chemical Bank 1,522,711 9.5 641,457 4.0 641,457 4.0 801,822 5.0

Parent Company Only Financial50

Parent Company Only Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Parent Company Condensed Statement of Financial Position	Condensed financial statements of Chemical Financial Corporation (parent company) only follow: Condensed Statements of Financial Position December 31, (Dollars in thousands) 2017 2016 Assets Cash at subsidiary bank $ 5,761 $ 16,851 Investment in subsidiaries 2,673,858 2,654,458 Premises and equipment 3,931 4,051 Goodwill 1,092 1,092 Deferred tax asset 7,203 30,715 Other assets 31,459 32,869 Total assets $ 2,723,304 $ 2,740,036 Liabilities Other liabilities $ 18,877 $ 18,345 Non-revolving line-of-credit 19,963 124,625 Subordinated debentures 15,715 15,540 Total liabilities 54,555 158,510 Shareholders' equity 2,668,749 2,581,526 Total liabilities and shareholders' equity $ 2,723,304 $ 2,740,036
Parent Company Condensed Statement of Income	Condensed Statements of Income Years Ended December 31, (Dollars in thousands) 2017 2016 2015 Income Cash dividends from subsidiaries $ 165,000 $ 110,450 $ 56,860 Other income 921 151 144 Total income 165,921 110,601 57,004 Expenses Interest expense 3,076 1,816 761 Operating expenses 23,298 30,589 7,794 Total expenses 26,374 32,405 8,555 Income before income taxes and equity in undistributed net income of subsidiaries 139,547 78,196 48,449 Income tax benefit 12,670 11,378 2,582 Equity in undistributed net (loss) income of subsidiaries (2,694 ) 18,458 35,799 Net income $ 149,523 $ 108,032 $ 86,830
Parent Company Condensed Statement of Cash Flows	Condensed Statements of Cash Flows Years Ended December 31, (Dollars in thousands) 2017 2016 2015 Cash Flows From Operating Activities Net income $ 149,523 $ 108,032 $ 86,830 Adjustments to reconcile net income to net cash provided by operating activities: Share-based compensation expense 17,346 13,452 3,478 Depreciation of premises and equipment 408 355 318 Equity in undistributed net loss (income) of subsidiaries 2,694 (18,458 ) (35,799 ) Net decrease in other assets 1,410 9,752 2,873 Net increase (decrease) in other liabilities 25,178 (11,830 ) (19,033 ) Net cash provided by operating activities 196,559 101,303 38,667 Cash Flows From Investing Activities Cash paid, net of cash assumed, in business combinations — (107,622 ) (45,267 ) Purchases of premises and equipment, net (288 ) (774 ) (320 ) Net cash used in investing activities (288 ) (108,396 ) (45,587 ) Cash Flows From Financing Activities Cash dividends paid (78,498 ) (49,389 ) (36,918 ) Proceeds from issuance of common stock, net of issuance costs — — — Repayment of subordinated debt obligations — (18,558 ) — Repayments of other borrowings (105,000 ) (62,500 ) — Proceeds from issuance of other borrowings — 125,000 25,000 Proceeds from directors' stock purchase plan and exercise of stock options 3,991 1,572 2,473 Cash paid for payroll taxes upon conversion of restricted stock units (27,854 ) (1,065 ) (571 ) Net cash used in financing activities (207,361 ) (4,940 ) (10,016 ) Net decrease in cash and cash equivalents (11,090 ) (12,033 ) (16,936 ) Cash and cash equivalents at beginning of year 16,851 28,884 45,820 Cash and cash equivalents at end of year $ 5,761 $ 16,851 $ 28,884 Business combinations: Fair value of assets acquired (noncash) $ — $ 46,898 $ 10,304 Liabilities assumed — 58,309 42,019 Common stock and stock options issued — 1,504,811 159,904

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Numerator and denominator of the basic and diluted earnings per common share computations	The factors used in the earnings per share computation follow: For the years ended December 31, (In thousands, except per share data) 2017 2016 2015 Net income $ 149,523 $ 108,032 $ 86,830 Net income allocated to participating securities 495 166 — Net income allocated to common shareholders (1) $ 149,028 $ 107,866 $ 86,830 Weighted average common shares - issued 71,103 49,091 36,081 Average unvested restricted share awards (238 ) (139 ) — Weighted average common shares outstanding - basic 70,865 48,952 36,081 Effect of dilutive securities Weighted average common stock equivalents 648 651 272 Weighted average common shares outstanding - diluted 71,513 49,603 36,353 EPS available to common shareholders Basic earnings per common share $ 2.11 $ 2.21 $ 2.41 Diluted earnings per common share $ 2.08 $ 2.17 $ 2.39 (1) Net income allocated to common shareholders for basic and diluted earnings per share may differ under the two-class method as a result of adding common share equivalents for options and warrants to dilutive shares outstanding, which alters the ratio used to allocate net income to common shareholders and participating securities for the purposes of calculating diluted earnings per share.

Accumulated Other Comprehensi52

Accumulated Other Comprehensive Loss (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Components of accumulated other comprehensive loss, net of related tax benefit/expense	The following table summarizes the changes within each component of accumulated other comprehensive income (loss), net of related tax benefit/expense for the years ended December 31, 2017 , 2016 and 2015 : (Dollars in thousands) Unrealized gains Defined Benefit Pension Plans Unrealized gains (losses) on cash flow hedges, net of tax Total For the year ended December 31, 2017 Beginning balance $ (14,142 ) $ (25,894 ) $ — $ (40,036 ) Other comprehensive loss before reclassifications 826 8,457 2,771 12,054 Amounts reclassified from accumulated other comprehensive income 4,802 1,139 1,061 7,002 Net current period other comprehensive income (loss) 5,628 9,596 3,832 19,056 Reclassification of certain deferred tax effects (1) (1,834 ) (3,510 ) 826 (4,518 ) Ending balance $ (10,348 ) $ (19,808 ) $ 4,658 $ (25,498 ) For the year ended December 31, 2016 Beginning balance $ (1,888 ) $ (27,144 ) $ — $ (29,032 ) Other comprehensive income (loss) before reclassifications (12,170 ) (229 ) — (12,399 ) Amounts reclassified from accumulated other comprehensive income (84 ) 1,479 — 1,395 Net current period other comprehensive income (loss) (12,254 ) 1,250 — (11,004 ) Ending balance $ (14,142 ) $ (25,894 ) $ — $ (40,036 ) For the year ended December 31, 2015 Beginning balance $ (210 ) $ (32,243 ) $ — $ (32,453 ) Other comprehensive income (loss) before reclassifications (1,269 ) 2,443 — 1,174 Amounts reclassified from accumulated other comprehensive income (409 ) 2,656 — 2,247 Net current period other comprehensive income (loss) (1,678 ) 5,099 — 3,421 Ending balance $ (1,888 ) $ (27,144 ) $ — $ (29,032 ) (1) The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, see Note 1 for further information.
Summary of amounts reclassified out of accumulated other comprehensive income (loss)	The following table summarizes the amounts reclassified out of each component of accumulated other comprehensive income (loss) for the years ended December 31, 2017, 2016 and 2015: (Dollars in thousands) Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Income Statement December 31, 2017 December 31, 2016 December 31, 2015 Gains and losses on available-for-sale securities $ (7,388 ) $ 129 $ 630 Net gain on sale of investment securities (noninterest income) 2,586 (45 ) (221 ) Income tax (expense)/benefit $ (4,802 ) $ 84 $ 409 Net Income Amortization of defined benefit pension plan items $ (1,752 ) $ (2,276 ) $ (4,086 ) Salaries, wages and employee benefits (operating expenses) 613 797 1,430 Income tax (expense)/benefit $ (1,139 ) $ (1,479 ) $ (2,656 ) Net Income Gains and losses on cash flow hedges 1,633 — — Interest on short-term borrowings (interest expense) (572 ) — — Income tax (expense)/benefit $ 1,061 $ — $ — Net Income (loss)

Summary of Quarterly Statemen53

Summary of Quarterly Statements of Income (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Schedule of Quarterly Financial Information	The following is a summary of the unaudited quarterly results of operation for the years ended December 31, 2017 , 2016 and 2015 . In the opinion of management, the information reflects all adjustments that are necessary for the fair presentation of the results of operations for the periods presented. 2017 (Dollars in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Total Interest income $ 142,896 $ 155,133 $ 164,944 $ 169,162 $ 632,135 Interest expense 12,799 17,185 21,316 23,257 74,557 Net interest income 130,097 137,948 143,628 145,905 557,578 Provision for loan losses 4,050 6,229 5,499 7,522 23,300 Noninterest income 38,010 41,568 32,122 32,319 144,019 Operating expenses 104,196 98,237 119,539 100,022 421,994 Income before income taxes 59,861 75,050 50,712 70,680 256,303 Income tax expense 12,257 23,036 10,253 61,234 106,780 Net income $ 47,604 $ 52,014 $ 40,459 $ 9,446 $ 149,523 Net income per common share: Basic $ 0.67 $ 0.73 $ 0.57 $ 0.13 $ 2.11 Diluted 0.67 0.73 0.56 0.13 2.08 Cash dividends declared per common share 0.27 0.27 0.28 0.27 1.10 2016 (Dollars in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Total Interest income $ 79,464 $ 82,937 $ 103,562 $ 144,416 $ 410,379 Interest expense 5,134 5,442 6,753 11,969 29,298 Net interest income 74,330 77,495 96,809 132,447 381,081 Provision for loan losses 1,500 3,000 4,103 6,272 14,875 Noninterest income 19,419 20,897 27,770 54,264 122,350 Operating expenses 58,887 59,085 106,144 114,302 338,418 Income before income taxes 33,362 36,307 14,332 66,137 150,138 Income tax expense 9,757 10,532 2,848 18,969 42,106 Net income $ 23,605 $ 25,775 $ 11,484 $ 47,168 $ 108,032 Net income per common share: Basic $ 0.61 $ 0.67 $ 0.23 $ 0.67 $ 2.21 Diluted 0.60 0.67 0.23 0.66 2.17 Cash dividends declared per common share 0.26 0.26 0.27 0.27 1.06 2015 (Dollars in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Total Interest income $ 62,630 $ 69,679 $ 78,851 $ 80,629 $ 291,789 Interest expense 3,450 3,944 5,234 5,153 17,781 Net interest income 59,180 65,735 73,617 75,476 274,008 Provision for loan losses 1,500 1,500 1,500 2,000 6,500 Noninterest income 19,275 20,674 20,215 20,052 80,216 Operating expenses 51,020 56,785 58,265 57,824 223,894 Income before income taxes 25,935 28,124 34,067 35,704 123,830 Income tax expense 8,100 9,100 9,600 10,200 37,000 Net income $ 17,835 $ 19,024 $ 24,467 $ 25,504 $ 86,830 Net income per common share: Basic $ 0.54 $ 0.54 $ 0.64 $ 0.67 $ 2.41 Diluted 0.54 0.54 0.64 0.66 2.39 Cash dividends declared per common share 0.24 0.24 0.26 0.26 1.00

Summary of Significant Accoun54

Summary of Significant Accounting Policies (Nature of Operations) (Details)	12 Months Ended
	Dec. 31, 2017Bank
Nature of Operations
Number of banks through which company operates (in bank)	1
Number of regional banking units Chemical Bank operates through (in bank)	7

Summary of Significant Accoun55

Summary of Significant Accounting Policies (Nonmarketable Equity Securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
FHLB stock minimum redemption period	5 years
FRB stock minimum redemption period	6 months
FRB stock minimum annual amount redeemable	25.00%
Corporation's ownership in FHLB stock	$ 112	$ 58
Corporation's ownership in FRB stock	$ 68.1	$ 39.4

Summary of Significant Accoun56

Summary of Significant Accounting Policies (Originated Loans Held for Investment) (Details)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Number of minimum days when principal or interest is past due is placed in nonaccrual category	90 days
Time period in which payments receive consistently and loans are returned to accrual status	6 months

Summary of Significant Accoun57

Summary of Significant Accounting Policies (Loans Modified Under Troubled Debt Restructuring) (Details)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Number of minimum days when principal or interest is past due is placed in nonaccrual category	90 days
Time period of real estate residential troubled debt restructurings reducing borrower's monthly payments by decreasing the interest rate charged on the loan	24 months

Summary of Significant Accoun58

Summary of Significant Accounting Policies (Allowance for Loan Losses) (Details)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Period of weighted average losses for the calculation of the allowance for loan losses	6 years

Summary of Significant Accoun59

Summary of Significant Accounting Policies (Mortgage Banking Operations) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Change in accounting policy for ASC Subtopic 860-50
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cumulative adjustment to retained earnings	$ 3.7
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forward commitment term	90 days

Summary of Significant Accoun60

Summary of Significant Accounting Policies (Premises and Equipment) (Details)	12 Months Ended
	Dec. 31, 2017
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	25 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	40 years
All other depreciable assets | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	3 years
All other depreciable assets | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	10 years

Summary of Significant Accoun61

Summary of Significant Accounting Policies (Other Real Estate Owned and Repossessed Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Interest receivable and other assets
Other real estate owned and repossessed assets	$ 8.8	$ 17.2

Summary of Significant Accoun62

Summary of Significant Accounting Policies (Other Intangible Assets) (Details)	12 Months Ended
	Dec. 31, 2017
Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period	10 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period	15 years
Core deposit intangible assets | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period	10 years
Core deposit intangible assets | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period	15 years

Summary of Significant Accoun63

Summary of Significant Accounting Policies (Bank-Owned Life Insurance) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Bank-owned life insurance	$ 147.6	$ 143.7
Bank owned life insurance income	$ 4.8	$ 1.8	$ 0.6

Summary of Significant Accoun64

Summary of Significant Accounting Policies (Long-Term Borrowings) (Details)	Dec. 31, 2017
Accounting Policies [Abstract]
Percentage of FHLB advances secured by first lien real estate residential loans	140.00%

Summary of Significant Accoun65

Summary of Significant Accounting Policies (Advertising Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Advertising and marketing	$ 5.9	$ 3.7	$ 3.3

Summary of Significant Accoun66

Summary of Significant Accounting Policies (Income Taxes and Investment in Tax Credit Projects) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Contingent income tax liabilities recorded	$ 0	$ 0

Summary of Significant Accoun67

Summary of Significant Accounting Policies (Adopted Accounting Pronouncements) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	[1]
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification of certain income tax effects	$ 0
Retained Earnings
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification of certain income tax effects	$ 4,518
[1]	The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, refer to Note 1 for further details on the adoption.

Mergers and Acquisitions (Textu

Mergers and Acquisitions (Textual) (Details) $ / shares in Units, $ in Thousands	Aug. 31, 2016USD ($)$ / sharesshares	May 31, 2015USD ($)office$ / sharesshares	Apr. 01, 2015USD ($)officeshares	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Business Acquisition
Credit facility drawn					$ 372,882	$ 597,847
Merger expenses					8,522	61,134	$ 7,804
Goodwill					1,134,568	1,133,534
Line of Credit
Business Acquisition
Credit facility drawn	$ 125,000				19,963	124,625
Repayments of lines of credit	25,000
Talmer
Business Acquisition
Acquisition purchase price	$ 1,612,449
Stock consideration given (in shares) | shares	32,100,000
Exchange ratio of common stock issued	0.4725
Share price (in dollars per share) | $ / shares	$ 1.61
Repayments of lines of credit	$ 37,500
Decrease in goodwill recognized				$ (1,000)
Cash paid	107,638
Total assets acquired	764,748
Goodwill	847,701
Intangibles acquired	$ 19,088
Lake Michigan
Business Acquisition
Acquisition purchase price		$ 187,394				187,394
Stock consideration given (in shares) | shares		4,300,000
Exchange ratio of common stock issued		1.326
Service provided by acquiree bank through number of branches (in office) | office		5
Share price (in dollars per share) | $ / shares		$ 16.64
Stock consideration given		$ 132,900
Cash paid		54,478
Total assets acquired		1,240,000
Loans		985,500				985,542
Total deposits acquired		924,700				924,697
Goodwill		101,061				101,061
Core deposits and other intangible assets acquired		$ 8,600
Acquisition related expenses							5,500
Intangibles acquired						8,003
Monarch
Business Acquisition
Acquisition purchase price			$ 27,191				27,191
Stock consideration given (in shares) | shares			860,575
Exchange ratio of common stock issued			0.0982
Service provided by acquiree bank through number of branches (in office) | office			5
Cash paid			$ 203
Total assets acquired			182,800
Loans							121,783
Total deposits acquired			144,300				144,300
Goodwill			$ 5,339				5,339
Acquisition related expenses							2,300
Intangibles acquired							$ 1,930
Outstanding contractual principal balance of acquired loan portfolio					76,000	92,400
Carrying amount of acquired loan portfolio					$ 70,800	$ 86,400

Mergers and Acquisitions (Asset

Mergers and Acquisitions (Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Aug. 31, 2016	May 31, 2015	Apr. 01, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Investment securities:
Goodwill				$ 1,133,534		$ 1,134,568
Bank-owned life insurance				143,700		147,600
Fair value of liabilities assumed:
Short-term borrowings				825,000		2,000,000
Long-term borrowings				597,847		$ 372,882
Talmer
Consideration paid:
Stock	$ 1,504,811
Cash	107,638
Total consideration	1,612,449
Fair value of identifiable assets acquired:
Cash and cash equivalents	433,352
Investment securities:
Available-for-sale	808,894
Held-to-maturity	1,657
Loans held-for-sale	244,916
Premises and equipment	38,793
Loan servicing rights	42,462
Other intangible assets	19,088
Interest receivable and other assets	395,539
Goodwill	847,701
Loans	4,882,402
Total identifiable assets acquired	6,867,103
Fair value of liabilities assumed:
Noninterest-bearing deposits	1,236,902
Interest-bearing deposits	4,057,716
Interest payable and other liabilities	100,936
Securities sold under agreements to repurchase with customers	19,704
Short-term borrowings	387,500
Long-term borrowings	299,597
Total liabilities assumed	6,102,355
Fair value of net identifiable assets acquired	$ 764,748
Lake Michigan
Consideration paid:
Stock		$ 132,916
Cash		54,478
Total consideration		187,394		187,394
Fair value of identifiable assets acquired:
Cash and cash equivalents				39,301
Investment securities				66,699
Investment securities:
Loans		985,500		985,542
Premises and equipment				10,975
Other intangible assets				8,003
Deferred tax asset, net				16,715
Goodwill		101,061		101,061
Bank-owned life insurance				23,844
Loans				37,695
Total identifiable assets acquired				1,289,835
Fair value of liabilities assumed:
Deposits		924,700		924,697
Short-term borrowings				30,000
Long-term borrowings				124,857
Other liabilities				22,887
Total liabilities assumed				$ 1,102,441
Fair value of net identifiable assets acquired		1,240,000
Shareholders' equity		89,280
Loans		(22,600)
Allowance for loan losses		15,888
Deferred tax assets, net		4,096
Premises and equipment		(5,031)
Core deposit intangibles		8,003
Deposits and borrowings, net		(3,182)
Other assets and other liabilities		(121)
Fair value of adjusted net assets acquired		$ 86,333
Monarch
Consideration paid:
Stock			$ 26,988
Cash			203
Total consideration			27,191		$ 27,191
Fair value of identifiable assets acquired:
Cash and cash equivalents					32,171
Investment securities:
Loans					121,783
Premises and equipment					3,019
Other intangible assets					1,930
Net operating loss carryforward					7,900
Deferred tax asset, net					2,392
Goodwill			5,339		5,339
Mortgage servicing rights					1,284
Loans					6,972
Total identifiable assets acquired					182,790
Fair value of liabilities assumed:
Deposits			144,300		144,300
Long-term borrowings					8,000
Other liabilities					3,299
Total liabilities assumed					$ 155,599
Fair value of net identifiable assets acquired			182,800
Shareholders' equity			15,270
Loans			(7,150)
Allowance for loan losses			2,128
Net operating loss carryforward			7,900
Other			1,826
Premises and equipment			(415)
Core deposit intangibles			1,930
Mortgage servicing rights			315
Other assets and other liabilities			48
Fair value of adjusted net assets acquired			$ 21,852

Mergers and Acquisitions (Loans

Mergers and Acquisitions (Loans Accounted for Under ASC 310-30) (Details) - USD ($) $ in Thousands	Aug. 31, 2016	May 31, 2015	Apr. 01, 2015
Talmer
Accounted for under ASC 310-30:
Contractual cash flows	$ 5,968,488
Contractual cash flows not expected to be collected (nonaccretable difference)	223,959
Expected cash flows	5,744,529
Interest component of expected cash flows (accretable yield)	862,127
Fair value at acquisition	$ 4,882,402
Lake Michigan
Accounted for under ASC 310-30:
Contractual cash flows		$ 1,198,388
Contractual cash flows not expected to be collected (nonaccretable difference)		22,600
Expected cash flows		1,175,788
Interest component of expected cash flows (accretable yield)		190,246
Fair value at acquisition		$ 985,542
Monarch
Accounted for under ASC 310-30:
Contractual cash flows			$ 166,797
Contractual cash flows not expected to be collected (nonaccretable difference)			7,100
Expected cash flows			159,697
Interest component of expected cash flows (accretable yield)			37,914
Fair value at acquisition			$ 121,783

Mergers and Acquisitions (Pro F

Mergers and Acquisitions (Pro Forma Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition
Net interest and other income	$ 701,597	$ 492,323	$ 654,962
Net Income	$ 149,523	$ 115,847	$ 142,504
Earnings per share:
Basic (in dollars per share)	$ 2.11	$ 1.65	$ 2.03
Diluted (in dollars per share)	$ 2.08	$ 1.62	$ 2.01

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	$ 1,963,546	$ 1,234,964
Loan servicing rights	63,841	48,085	$ 0
U.S. Treasury securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		5,793
Government sponsored agencies
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	202,916	215,011
State and political subdivisions
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	345,970	300,088
Residential mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	150,131	272,282
Collateralized mortgage obligations
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,033,845	320,025
Corporate bonds
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	192,794	89,474
Preferred stock and trust preferred securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	37,890	32,291
Recurring
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,963,546	1,234,964
Loans held-for-sale	52,133	81,830
Loan servicing rights	63,841	48,085
Derivative assets	18,681	8,215
Total assets at fair value	2,098,201	1,373,094
Derivative liabilities	12,357	6,359
Total liabilities at fair value	12,357	6,359
Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	5,793
Loans held-for-sale	0	0
Loan servicing rights	0	0
Derivative assets	0	0
Total assets at fair value	0	5,793
Derivative liabilities	0	0
Total liabilities at fair value	0	0
Recurring | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,963,546	1,229,171
Loans held-for-sale	52,133	81,830
Loan servicing rights	0	0
Derivative assets	18,681	8,215
Total assets at fair value	2,034,360	1,319,216
Derivative liabilities	12,357	6,359
Total liabilities at fair value	12,357	6,359
Recurring | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Loans held-for-sale	0	0
Loan servicing rights	63,841	48,085
Derivative assets	0	0
Total assets at fair value	63,841	48,085
Derivative liabilities	0	0
Total liabilities at fair value	0	0
Recurring | Customer-initiated derivatives
Summary of assets measured at fair value on a recurring basis
Derivative assets	9,376	4,406
Derivative liabilities	10,139	4,141
Recurring | Customer-initiated derivatives | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Customer-initiated derivatives | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	9,376	4,406
Derivative liabilities	10,139	4,141
Recurring | Customer-initiated derivatives | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Forward contracts related to mortgage loans to be delivered for sale
Summary of assets measured at fair value on a recurring basis
Derivative assets		635
Derivative liabilities	34
Recurring | Forward contracts related to mortgage loans to be delivered for sale | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets		0
Derivative liabilities	0
Recurring | Forward contracts related to mortgage loans to be delivered for sale | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets		635
Derivative liabilities	34
Recurring | Forward contracts related to mortgage loans to be delivered for sale | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets		0
Derivative liabilities	0
Recurring | Interest rate lock commitments
Summary of assets measured at fair value on a recurring basis
Derivative assets	1,222	956
Recurring | Interest rate lock commitments | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Recurring | Interest rate lock commitments | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	1,222	956
Recurring | Interest rate lock commitments | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Recurring | Power Equity CD
Summary of assets measured at fair value on a recurring basis
Derivative assets	2,184	2,218
Derivative liabilities	2,184	2,218
Recurring | Power Equity CD | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Power Equity CD | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	2,184	2,218
Derivative liabilities	2,184	2,218
Recurring | Power Equity CD | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Risk management derivatives
Summary of assets measured at fair value on a recurring basis
Derivative assets	5,899
Recurring | Risk management derivatives | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0
Recurring | Risk management derivatives | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	5,899
Recurring | Risk management derivatives | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0
Recurring | U.S. Treasury securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		5,793
Recurring | U.S. Treasury securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		5,793
Recurring | U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | U.S. Treasury securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | Government sponsored agencies
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	202,916	215,011
Recurring | Government sponsored agencies | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Government sponsored agencies | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	202,916	215,011
Recurring | Government sponsored agencies | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | State and political subdivisions
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	345,970	300,088
Recurring | State and political subdivisions | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | State and political subdivisions | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	345,970	300,088
Recurring | State and political subdivisions | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	150,131
Recurring | Mortgage-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0
Recurring | Mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	150,131
Recurring | Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0
Recurring | Residential mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		272,282
Recurring | Residential mortgage-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | Residential mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		272,282
Recurring | Residential mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | Collateralized mortgage obligations
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,033,845	320,025
Recurring | Collateralized mortgage obligations | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Collateralized mortgage obligations | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,033,845	320,025
Recurring | Collateralized mortgage obligations | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Corporate bonds
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	192,794	89,474
Recurring | Corporate bonds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Corporate bonds | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	192,794	89,474
Recurring | Corporate bonds | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Preferred stock and trust preferred securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	37,890	32,291
Recurring | Preferred stock and trust preferred securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Preferred stock and trust preferred securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	37,890	32,291
Recurring | Preferred stock and trust preferred securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	$ 0	$ 0

Fair Value Measurements (Change

Fair Value Measurements (Changes in Level 3 Assets) (Details) - Recurring - Loan servicing rights - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 48,085	$ 0
Additions due to acquisition	0	42,462
Transfer in based on new accounting policy election	15,891	0
Gains (losses) recorded in earnings (realized) recorded in Net gain on sale of loans and other mortgage banking revenue	(8,880)	4,593
New originations	8,745	1,030
Balance, end of period	$ 63,841	$ 48,085

Fair Value Measurements (Aggreg

Fair Value Measurements (Aggregate Fair Value, Contractual Balance, and Gain or Loss for Loans Held-For-Sale) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Aggregate fair value	$ 52,133	$ 81,830
Contractual balance	50,597	81,009
Unrealized gain (loss)	$ 1,536	$ 821

Fair Value Measurements (Gains

Fair Value Measurements (Gains (Losses) from Loans Held-for-Sale Included in the Consolidated Statements of Income) (Details) - Loans held for sale - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total included in earnings	$ 34,989	$ 17,331	$ 6,376
Interest income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total included in earnings	2,540	1,606	83
Net gain (loss) on sale of loans and other mortgage banking revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total included in earnings	715	39	(61)
Net gain on sales of loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total included in earnings	$ 31,734	$ 15,686	$ 6,354

Fair Value Measurements (Nonrec

Fair Value Measurements (Nonrecurring Basis) (Details) - Nonrecurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	$ 73,518	$ 63,572
Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	73,518	63,572
Impaired loans
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis		62,184
Impaired loans | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	70,619	62,184
Other real estate and repossessed assets
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	2,899	1,386
Other real estate and repossessed assets | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	$ 2,899	1,386
Loan servicing rights
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis		2
Loan servicing rights | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis		$ 2

Fair Value Measurements (Textua

Fair Value Measurements (Textual) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale on nonaccrual status	$ 0	$ 0
Impairment of goodwill	0	0
Impairment identified for intangible assets	0	0
Loans held for sale 90 days past due and on accrual status	0	0
Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities recorded at fair value	$ 0	0
Non-compete intangible assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Finite-lived intangible assets amortization period	1 year
Loan Servicing Rights
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Valuation allowance related to impairment		$ 8,000	$ 0
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount factors used to determine fair value	20.00%
Finite-lived intangible assets amortization period	10 years
Minimum | Other Real Estate and Repossessed Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount factors used to determine fair value	20.00%
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount factors used to determine fair value	30.00%
Finite-lived intangible assets amortization period	15 years
Maximum | Other Real Estate and Repossessed Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount factors used to determine fair value	30.00%

Fair Value Measurements (Level

Fair Value Measurements (Level 3 Assets Measured on a Nonrecurring Basis) (Details) - Nonrecurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total assets measured at fair value on a nonrecurring basis	$ 73,518	$ 63,572
Impaired loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total assets measured at fair value on a nonrecurring basis		62,184
Other real estate and repossessed assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total assets measured at fair value on a nonrecurring basis	2,899	1,386
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total assets measured at fair value on a nonrecurring basis	73,518	63,572
Level 3 | Impaired loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total assets measured at fair value on a nonrecurring basis	$ 70,619	62,184
Level 3 | Impaired loans | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate (as a percent)	20.00%
Level 3 | Impaired loans | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate (as a percent)	30.00%
Level 3 | Other real estate and repossessed assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total assets measured at fair value on a nonrecurring basis	$ 2,899	$ 1,386
Level 3 | Other real estate and repossessed assets | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate (as a percent)	20.00%
Level 3 | Other real estate and repossessed assets | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate (as a percent)	30.00%
Level 3 | Loan Servicing Rights | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate (as a percent)	10.00%
Prepayment speed (as a percent)	9.00%
Level 3 | Loan Servicing Rights | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate (as a percent)	11.00%
Prepayment speed (as a percent)	18.00%

Fair Value Measurements (Carryi

Fair Value Measurements (Carrying Amounts and Estimated Fair Values) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment securities:
Held-to-maturity	$ 662,906	$ 608,531
Bank-owned life insurance	147,600	143,700
Deposits without defined maturities
Short-term borrowings	2,000,000	825,000
Long-term borrowings	372,882	597,847
Nonrecurring
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis	73,518	63,572
Nonrecurring | Impaired loans
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis		62,184
Level 3 | Nonrecurring
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis	73,518	63,572
Level 3 | Nonrecurring | Impaired loans
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis	70,619	62,184
Carrying Amount | Level 1
Financial assets:
Cash and cash equivalents	455,991	474,402
Carrying Amount | Level 2
Investment securities:
Held-to-maturity	676,593	622,927
Nonmarketable equity securities	180,091	97,350
Interest receivable	50,710	42,235
Bank-owned life insurance	147,584	143,718
Deposits without defined maturities
Deposits without defined maturities	10,425,596	9,862,755
Time deposits	3,217,207	3,010,367
Total deposits	13,642,803	12,873,122
Interest payable	6,329	5,415
Securities sold under agreements to repurchase with customers	415,236	343,047
Short-term borrowings	2,000,000	825,000
Long-term borrowings	372,882	597,847
Carrying Amount | Level 3
Investment securities:
Held-to-maturity	500	500
Net loans	14,063,380	12,912,511
Fair Value | Level 1
Financial assets:
Cash and cash equivalents	455,991	474,402
Fair Value | Level 2
Investment securities:
Held-to-maturity	662,516	608,221
Nonmarketable equity securities	180,091	97,350
Interest receivable	50,710	42,235
Bank-owned life insurance	147,584	143,718
Deposits without defined maturities
Deposits without defined maturities	10,425,596	9,862,755
Time deposits	3,225,847	3,010,048
Total deposits	13,651,443	12,872,803
Interest payable	6,329	5,415
Securities sold under agreements to repurchase with customers	415,236	343,047
Short-term borrowings	1,999,137	825,000
Long-term borrowings	367,984	591,227
Fair Value | Level 3
Investment securities:
Held-to-maturity	390	310
Net loans	$ 14,114,545	$ 13,069,315

Investment Securities (Summary

Investment Securities (Summary of Amortized Cost and Fair Value of Available-for-Sale Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Securities Available-for-Sale
Amortized Cost	$ 1,976,646	$ 1,256,721
Unrealized Gains	4,040	1,566
Unrealized Losses	17,140	23,323
Available-for-sale, at fair value	1,963,546	1,234,964
U.S. Treasury securities
Investment Securities Available-for-Sale
Amortized Cost		5,788
Unrealized Gains		5
Unrealized Losses		0
Available-for-sale, at fair value		5,793
Government sponsored agencies
Investment Securities Available-for-Sale
Amortized Cost	203,099	216,890
Unrealized Gains	765	189
Unrealized Losses	948	2,068
Available-for-sale, at fair value	202,916	215,011
State and political subdivisions
Investment Securities Available-for-Sale
Amortized Cost	350,088	311,704
Unrealized Gains	310	163
Unrealized Losses	4,428	11,779
Available-for-sale, at fair value	345,970	300,088
Residential mortgage-backed securities
Investment Securities Available-for-Sale
Amortized Cost	151,752	276,162
Unrealized Gains	5	112
Unrealized Losses	1,626	3,992
Available-for-sale, at fair value	150,131	272,282
Collateralized mortgage obligations
Investment Securities Available-for-Sale
Amortized Cost	1,042,240	323,965
Unrealized Gains	89	63
Unrealized Losses	8,484	4,003
Available-for-sale, at fair value	1,033,845	320,025
Corporate bonds
Investment Securities Available-for-Sale
Amortized Cost	193,230	90,859
Unrealized Gains	1,156	16
Unrealized Losses	1,592	1,401
Available-for-sale, at fair value	192,794	89,474
Preferred stock and trust preferred securities
Investment Securities Available-for-Sale
Amortized Cost	36,237	31,353
Unrealized Gains	1,715	1,018
Unrealized Losses	62	80
Available-for-sale, at fair value	$ 37,890	$ 32,291

Investment Securities (Summar81

Investment Securities (Summary of Amortized Cost and Fair Value of Held-to-Maturity Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Securities Held-to-Maturity
Amortized Cost	$ 677,093	$ 623,427
Unrecognized Gains	3,856	2,648
Unrecognized Losses	18,043	17,544
Fair Value	662,906	608,531
State and political subdivisions
Investment Securities Held-to-Maturity
Amortized Cost	676,593	622,927
Unrecognized Gains	3,856	2,648
Unrecognized Losses	17,933	17,354
Fair Value	662,516	608,221
Trust preferred securities
Investment Securities Held-to-Maturity
Amortized Cost	500	500
Unrecognized Gains	0	0
Unrecognized Losses	110	190
Fair Value	$ 390	$ 310

Investment Securities (Gains an

Investment Securities (Gains and (Losses) Recognized in Earnings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Proceeds	$ 409,220	$ 41,446	$ 40,301
Gross gains	178	325	631
Gross losses	$ (7,566)	$ (196)	$ (1)

Investment Securities (Summar83

Investment Securities (Summary of the Amortized Cost and Fair Value of Investment Securities by Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Securities Available-for-Sale: Amortized Cost
Due in one year or less	$ 300,364
Due after one year through five years	751,998
Due after five years through ten years	616,027
Due after ten years	306,868
Preferred stock	1,389
Total	1,976,646
Investment Securities Available-for-Sale: Fair Value
Due in one year or less	298,644
Due after one year through five years	746,082
Due after five years through ten years	611,822
Due after ten years	305,174
Preferred stock	1,824
Total	1,963,546
Investment Securities Held-to-Maturity: Amortized Cost
Due in one year or less	89,359
Due after one year through five years	237,113
Due after five years through ten years	152,299
Due after ten years	198,322
Total	677,093	$ 623,427
Investment Securities Held-to-Maturity: Fair Value
Due in one year or less	89,149
Due after one year through five years	233,022
Due after five years through ten years	148,185
Due after ten years	192,550
Total	$ 662,906	$ 608,531

Investment Securities (Textual)

Investment Securities (Textual) (Details) $ in Millions	Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)
Investments, Debt and Equity Securities [Abstract]
Securities pledged as collateral | $	$ 937.2	$ 794
Number of securities in portfolio (in security)	2,329
Number of securities in an unrealized loss position in portfolio (in security)	1,518

Investment Securities (Summar85

Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 1,379,705	$ 1,478,240
Less Than 12 Months, Gross Unrealized Losses	21,534	39,116
12 Months or More, Fair Value	563,188	56,897
12 Months or More, Gross Unrealized Losses	13,649	1,751
Total, Fair Value	1,942,893	1,535,137
Total, Gross Unrealized Losses	35,183	40,867
Government sponsored agencies
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	63,818	105,702
Less Than 12 Months, Gross Unrealized Losses	510	1,707
12 Months or More, Fair Value	24,621	15,023
12 Months or More, Gross Unrealized Losses	438	361
Total, Fair Value	88,439	120,725
Total, Gross Unrealized Losses	948	2,068
State and political subdivisions
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	437,407	758,063
Less Than 12 Months, Gross Unrealized Losses	12,268	28,158
12 Months or More, Fair Value	349,242	26,810
12 Months or More, Gross Unrealized Losses	10,093	975
Total, Fair Value	786,649	784,873
Total, Gross Unrealized Losses	22,361	29,133
Residential mortgage-backed securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	93,508	244,239
Less Than 12 Months, Gross Unrealized Losses	383	3,992
12 Months or More, Fair Value	56,576	0
12 Months or More, Gross Unrealized Losses	1,243	0
Total, Fair Value	150,084	244,239
Total, Gross Unrealized Losses	1,626	3,992
Collateralized mortgage obligations
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	713,525	279,001
Less Than 12 Months, Gross Unrealized Losses	7,235	3,778
12 Months or More, Fair Value	73,707	14,754
12 Months or More, Gross Unrealized Losses	1,249	225
Total, Fair Value	787,232	293,755
Total, Gross Unrealized Losses	8,484	4,003
Corporate bonds
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	71,447	80,536
Less Than 12 Months, Gross Unrealized Losses	1,138	1,401
12 Months or More, Fair Value	47,878	0
12 Months or More, Gross Unrealized Losses	454	0
Total, Fair Value	119,325	80,536
Total, Gross Unrealized Losses	1,592	1,401
Preferred stock and trust preferred securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	10,699
Less Than 12 Months, Gross Unrealized Losses	0	80
12 Months or More, Fair Value	11,164	310
12 Months or More, Gross Unrealized Losses	172	190
Total, Fair Value	11,164	11,009
Total, Gross Unrealized Losses	$ 172	$ 270

Loans (Textual) (Details)

Loans (Textual) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Segmenttenantloanemployee	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of portfolio segment | Segment	2
Number of classes of loans | loan	6
Minimum number of tenants leased to for non-owner occupied real estate | tenant	1
Loans held-for-sale, at fair value	$ 52,133	$ 81,830
Loans held-for-sale, recorded investment sold	806,800	707,800	$ 222,600
Minimum value of loan requires regional loan committee approval	3,000
Maximum value of loan requires regional loan committee approval	$ 7,000
Minimum due period of loans consider in a nonperforming status	90 days
Nonaccrual TDRs reported in nonaccrual loans	$ 29,100	30,500
Interest income recognized on nonaccrual loans while in accruing status	1,300	400	900
Interest lost on nonaccrual loans	3,100	2,900	3,200
Interest income recognized on TDRs	2,600	3,900	$ 3,900
Real estate properties for which formal foreclosure proceedings are in process	4,200
Residential mortgage loans in process of foreclosure		7,300
Impaired loans	77,888	93,066
Commitments to lend additional funds to borrowers whose terms have been modified in TDRs	2,000
Management
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to directors, executive officers and affiliates	3,800	23,900
Loans to directors, executive officers and affiliates, current year additions	44,100	33,800
Loans to directors, executive officers and affiliates, current year reductions	64,200	31,600
Fixed-Rate Real Estate Residential Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-sale, at fair value		81,800
Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	48,782	62,535
Commercial Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	58,842	70,785
Commercial Loan Portfolio | Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	$ 34,484	$ 45,388
Land Development Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum period for payment of loan	12 months
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for loan secured under real estate residential security	15 years
Loan-to-value ratio at the time of origination	80.00%
Residential mortgage | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower limit of number of family residential properties | tenant	1
Residential mortgage | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Upper limit of number of family residential properties | tenant	4
Commercial | Commercial Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum value of loan requires group loan authority approval	$ 3,000
Number of bank executives and senior officers with credit decision limits similar to group loan authorities | employee	6
Maximum value of loan requires executive and senior officer approval	$ 8,000
Minimum value of loan requires group loan authority approval	$ 5,000
Commercial Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum due period of loans consider in a nonperforming status	90 days
Consumer Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Original contractual terms	90 days
Minimum due period of loans consider in a nonperforming status	90 days

Loans (Summary of Loans) (Detai

Loans (Summary of Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of loans under portfolio
Loans	$ 14,155,267	$ 12,990,779
Deferred costs	26,100	14,800
Commercial
Summary of loans under portfolio
Loans		3,217,300
Commercial real estate
Summary of loans under portfolio
Loans		3,973,140
Real estate construction and land development
Summary of loans under portfolio
Loans		403,772
Residential mortgage
Summary of loans under portfolio
Loans		3,086,474
Consumer installment
Summary of loans under portfolio
Loans		1,433,884
Home equity
Summary of loans under portfolio
Loans		876,209
Commercial Originated Portfolio
Summary of loans under portfolio
Loans	5,657,186	4,105,049
Commercial Originated Portfolio | Commercial
Summary of loans under portfolio
Loans	2,407,606	1,901,526
Commercial Originated Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	2,751,425	1,921,799
Commercial Originated Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	498,155	281,724
Consumer Originated Portfolio
Summary of loans under portfolio
Loans	4,090,243	3,353,352
Consumer Originated Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	1,967,857	1,475,342
Consumer Originated Portfolio | Consumer installment
Summary of loans under portfolio
Loans	1,510,540	1,282,588
Consumer Originated Portfolio | Home equity
Summary of loans under portfolio
Loans	611,846	595,422
Originated Portfolio
Summary of loans under portfolio
Loans	9,747,429	7,458,401
Originated Portfolio | Commercial
Summary of loans under portfolio
Loans	2,407,606	1,901,526
Originated Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	2,751,425	1,921,799
Originated Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	498,155	281,724
Originated Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	1,967,857	1,475,342
Originated Portfolio | Consumer installment
Summary of loans under portfolio
Loans	1,510,540	1,282,588
Originated Portfolio | Home equity
Summary of loans under portfolio
Loans	611,846	595,422
Commercial Acquired Portfolio
Summary of loans under portfolio
Loans	2,803,341	3,489,163
Commercial Acquired Portfolio | Commercial
Summary of loans under portfolio
Loans	978,036	1,315,774
Commercial Acquired Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	1,749,245	2,051,341
Commercial Acquired Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	76,060	122,048
Consumer Acquired Portfolio
Summary of loans under portfolio
Loans	1,604,497	2,043,215
Consumer Acquired Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	1,284,630	1,611,132
Consumer Acquired Portfolio | Consumer installment
Summary of loans under portfolio
Loans	102,468	151,296
Consumer Acquired Portfolio | Home equity
Summary of loans under portfolio
Loans	217,399	280,787
Acquired Portfolio
Summary of loans under portfolio
Loans	4,407,838	5,532,378
Commercial Loan Portfolio
Summary of loans under portfolio
Loans	8,460,527	7,594,212
Commercial Loan Portfolio | Commercial
Summary of loans under portfolio
Loans	3,385,642
Commercial Loan Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	4,500,670
Commercial Loan Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	574,215
Consumer Loan Portfolio
Summary of loans under portfolio
Loans	5,694,740	5,396,567
Consumer Loan Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	3,252,487	3,086,474
Consumer Loan Portfolio | Consumer installment
Summary of loans under portfolio
Loans	1,613,008	1,433,884
Consumer Loan Portfolio | Home equity
Summary of loans under portfolio
Loans	$ 829,245	$ 876,209

Loans (Activity for Accretable

Loans (Activity for Accretable Yield) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 1,039,971	$ 298,257	$ 137,961
Addition attributable to acquisitions		862,127	228,160
Additions (reductions)		(11,354)	(8,450)
Accretion recognized in interest income	(242,169)	(131,559)	(59,414)
Net reclassification (to) from nonaccretable difference	129,095	22,500	0
Balance at end of period	926,897	1,039,971	298,257
Talmer
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	798,210	0	0
Addition attributable to acquisitions		862,127	0
Additions (reductions)		0	0
Accretion recognized in interest income	(175,678)	(63,917)	0
Net reclassification (to) from nonaccretable difference	108,821	0	0
Balance at end of period	731,353	798,210	0
Lake Michigan
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	121,416	152,999	0
Addition attributable to acquisitions		0	190,246
Additions (reductions)		(3,552)	(12,991)
Accretion recognized in interest income	(29,077)	(33,031)	(24,256)
Net reclassification (to) from nonaccretable difference	2,785	5,000	0
Balance at end of period	95,124	121,416	152,999
Monarch
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	27,182	34,558	0
Addition attributable to acquisitions		0	37,914
Additions (reductions)		(1,908)	1,336
Accretion recognized in interest income	(4,533)	(5,468)	(4,692)
Net reclassification (to) from nonaccretable difference	(153)	0	0
Balance at end of period	22,496	27,182	34,558
Northwestern
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	69,847	82,623	104,675
Addition attributable to acquisitions		0	0
Additions (reductions)		(6,985)	(3,396)
Accretion recognized in interest income	(20,318)	(15,791)	(18,656)
Net reclassification (to) from nonaccretable difference	11,285	10,000	0
Balance at end of period	60,814	69,847	82,623
OAK
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	23,316	28,077	33,286
Addition attributable to acquisitions		0	0
Additions (reductions)		1,091	6,601
Accretion recognized in interest income	(12,563)	(13,352)	(11,810)
Net reclassification (to) from nonaccretable difference	6,357	7,500	0
Balance at end of period	$ 17,110	$ 23,316	$ 28,077

Loans (Summary of Recorded Inve

Loans (Summary of Recorded Investment of Commercial Loans by Risk Rating Categories) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 14,155,267	$ 12,990,779
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans		3,217,300
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans		3,973,140
Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans		403,772
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	8,460,527	7,594,212
Commercial Portfolio Segment [Member] | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,038,463	7,167,397
Commercial Portfolio Segment [Member] | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	204,706	192,013
Commercial Portfolio Segment [Member] | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	216,353	233,479
Commercial Portfolio Segment [Member] | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	1,005	1,323
Commercial Portfolio Segment [Member] | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	3,385,642
Commercial Portfolio Segment [Member] | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	4,500,670
Commercial Portfolio Segment [Member] | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	574,215
Commercial Originated Portfolio
Financing Receivable, Recorded Investment [Line Items]
Loans	5,657,186	4,105,049
Commercial Originated Portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,488,571	3,934,033
Commercial Originated Portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	66,100	81,947
Commercial Originated Portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	102,515	87,999
Commercial Originated Portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1,070
Commercial Originated Portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	2,407,606	1,901,526
Commercial Originated Portfolio | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,316,464	1,803,750
Commercial Originated Portfolio | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	41,059	44,809
Commercial Originated Portfolio | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	50,083	51,898
Commercial Originated Portfolio | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1,069
Commercial Originated Portfolio | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,751,425	1,921,799
Commercial Originated Portfolio | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,677,579	1,849,315
Commercial Originated Portfolio | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	24,204	36,981
Commercial Originated Portfolio | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	49,642	35,502
Commercial Originated Portfolio | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1
Commercial Originated Portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	498,155	281,724
Commercial Originated Portfolio | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	494,528	280,968
Commercial Originated Portfolio | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	837	157
Commercial Originated Portfolio | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	2,790	599
Commercial Originated Portfolio | Real estate construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Acquired Portfolio
Financing Receivable, Recorded Investment [Line Items]
Loans	2,803,341	3,489,163
Commercial Acquired Portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,549,892	3,233,364
Commercial Acquired Portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	138,606	110,066
Commercial Acquired Portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	113,838	145,480
Commercial Acquired Portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	1,005	253
Commercial Acquired Portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	978,036	1,315,774
Commercial Acquired Portfolio | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	873,861	1,218,848
Commercial Acquired Portfolio | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	68,418	46,643
Commercial Acquired Portfolio | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	35,539	50,283
Commercial Acquired Portfolio | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	218	0
Commercial Acquired Portfolio | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,749,245	2,051,341
Commercial Acquired Portfolio | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,603,685	1,897,011
Commercial Acquired Portfolio | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	67,970	61,441
Commercial Acquired Portfolio | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	76,803	92,636
Commercial Acquired Portfolio | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	787	253
Commercial Acquired Portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	76,060	122,048
Commercial Acquired Portfolio | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	72,346	117,505
Commercial Acquired Portfolio | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	2,218	1,982
Commercial Acquired Portfolio | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	1,496	2,561
Commercial Acquired Portfolio | Real estate construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0

Loans (Summary of Recorded In90

Loans (Summary of Recorded Investment of Consumer Loans by Risk Rating Categories) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 14,155,267	$ 12,990,779
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans		3,086,474
Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Loans		1,433,884
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans		876,209
Consumer Loan Portfolio
Financing Receivable, Recorded Investment [Line Items]
Loans	5,694,740	5,396,567
Consumer Loan Portfolio | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	3,252,487	3,086,474
Consumer Loan Portfolio | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Loans	1,613,008	1,433,884
Consumer Loan Portfolio | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	829,245	876,209
Consumer Originated Portfolio
Financing Receivable, Recorded Investment [Line Items]
Loans	4,090,243	3,353,352
Consumer Originated Portfolio | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	4,076,461	3,342,153
Consumer Originated Portfolio | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans	13,782	11,199
Consumer Originated Portfolio | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	1,967,857	1,475,342
Consumer Originated Portfolio | Residential mortgage | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,959,222	1,468,373
Consumer Originated Portfolio | Residential mortgage | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans	8,635	6,969
Consumer Originated Portfolio | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Loans	1,510,540	1,282,588
Consumer Originated Portfolio | Consumer installment | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,509,698	1,281,709
Consumer Originated Portfolio | Consumer installment | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans	842	879
Consumer Originated Portfolio | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	611,846	595,422
Consumer Originated Portfolio | Home equity | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	607,541	592,071
Consumer Originated Portfolio | Home equity | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans	4,305	3,351
Consumer Acquired Portfolio
Financing Receivable, Recorded Investment [Line Items]
Loans	1,604,497	2,043,215
Consumer Acquired Portfolio | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	1,284,630	1,611,132
Consumer Acquired Portfolio | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Loans	102,468	151,296
Consumer Acquired Portfolio | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 217,399	$ 280,787

Loans (Summary of Nonperforming

Loans (Summary of Nonperforming Loans) (Details) - Nonperforming - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of nonperforming loans
Total nonaccrual loans	$ 63,095	$ 44,334
Other real estate owned and repossessed assets	8,807	17,187
Total nonperforming assets	71,902	61,521
Total accruing loans contractually past due 90 days or more as to interest or principal payments	1,377	1,283
Commercial Loan Portfolio | Commercial
Summary of nonperforming loans
Total nonaccrual loans	19,691	13,178
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	11
Commercial Loan Portfolio | Commercial real estate
Summary of nonperforming loans
Total nonaccrual loans	29,545	19,877
Total accruing loans contractually past due 90 days or more as to interest or principal payments	13	277
Commercial Loan Portfolio | Real estate construction and land development
Summary of nonperforming loans
Total nonaccrual loans	77	80
Consumer Loan Portfolio | Residential mortgage
Summary of nonperforming loans
Total nonaccrual loans	8,635	6,969
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0
Consumer Loan Portfolio | Consumer installment
Summary of nonperforming loans
Total nonaccrual loans	842	879
Consumer Loan Portfolio | Home equity
Summary of nonperforming loans
Total nonaccrual loans	4,305	3,351
Total accruing loans contractually past due 90 days or more as to interest or principal payments	$ 1,364	$ 995

Loans (Summary of the Aging Sta

Loans (Summary of the Aging Status of the Recorded Investment in Loans by Portfolio Segment/Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule representing the aging status of the recorded investment in loans by classes
Total loans	$ 14,155,267	$ 12,990,779
Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total loans		3,217,300
Commercial real estate
Schedule representing the aging status of the recorded investment in loans by classes
Total loans		3,973,140
Real estate construction and land development
Schedule representing the aging status of the recorded investment in loans by classes
Total loans		403,772
Residential mortgage
Schedule representing the aging status of the recorded investment in loans by classes
Total loans		3,086,474
Consumer installment
Schedule representing the aging status of the recorded investment in loans by classes
Total loans		1,433,884
Home equity
Schedule representing the aging status of the recorded investment in loans by classes
Total loans		876,209
Originated Portfolio
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	58,857	51,633
Current	9,688,572	7,406,768
Total loans	9,747,429	7,458,401
Financing receivable, recorded investment accruing loans past due 90 days or more	1,377	1,283
Originated Portfolio | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	31,724	29,928
Originated Portfolio | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	8,486	8,560
Originated Portfolio | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	18,647	13,145
Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	27,166	18,904
Current	2,380,440	1,882,622
Total loans	2,407,606	1,901,526
Financing receivable, recorded investment accruing loans past due 90 days or more	0	11
Originated Portfolio | Commercial | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	13,906	10,421
Originated Portfolio | Commercial | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	3,766	4,842
Originated Portfolio | Commercial | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	9,494	3,641
Originated Portfolio | Commercial real estate
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	16,815	13,305
Current	2,734,610	1,908,494
Total loans	2,751,425	1,921,799
Financing receivable, recorded investment accruing loans past due 90 days or more	13	277
Originated Portfolio | Commercial real estate | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	9,380	6,551
Originated Portfolio | Commercial real estate | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,562	1,589
Originated Portfolio | Commercial real estate | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	5,873	5,165
Originated Portfolio | Real estate construction and land development
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	0	3,220
Current	498,155	278,504
Total loans	498,155	281,724
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0
Originated Portfolio | Real estate construction and land development | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	0	2,721
Originated Portfolio | Real estate construction and land development | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	0	499
Originated Portfolio | Real estate construction and land development | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	0	0
Originated Portfolio | Residential mortgage
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	5,068	4,961
Current	1,962,789	1,470,381
Total loans	1,967,857	1,475,342
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0
Originated Portfolio | Residential mortgage | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	2,795	3,147
Originated Portfolio | Residential mortgage | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,415	62
Originated Portfolio | Residential mortgage | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	858	1,752
Originated Portfolio | Consumer installment
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	3,992	4,904
Current	1,506,548	1,277,684
Total loans	1,510,540	1,282,588
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0
Originated Portfolio | Consumer installment | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	3,324	3,991
Originated Portfolio | Consumer installment | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	442	675
Originated Portfolio | Consumer installment | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	226	238
Originated Portfolio | Home equity
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	5,816	6,339
Current	606,030	589,083
Total loans	611,846	595,422
Financing receivable, recorded investment accruing loans past due 90 days or more	1,364	995
Originated Portfolio | Home equity | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	2,319	3,097
Originated Portfolio | Home equity | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,301	893
Originated Portfolio | Home equity | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	$ 2,196	$ 2,349

Loans (Summary of Impaired Loan

Loans (Summary of Impaired Loans by Classes of Loans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired loans with a valuation allowance:
Recorded investment	$ 78,621	$ 74,740
Unpaid principal balance	87,956	85,264
Related valuation allowance	8,002	9,392
Average annual recorded investment	66,592	39,582	$ 33,090
Interest income recognized while on impaired status	2,250	1,285	1,312
Impaired loans with no related valuation allowance:
Recorded investment	33,256	32,129
Unpaid principal balance	35,824	38,794
Average annual recorded investment	41,151	73,864	87,093
Interest income recognized while on impaired status	325	2,601	2,577
Total impaired loans:
Recorded investment	111,877	106,869
Unpaid principal balance	123,780	124,058
Related valuation allowance	8,002	9,392
Average annual recorded investment	107,743	113,446	120,183
Interest income recognized while on impaired status	2,575	3,886	3,889
Commercial
Impaired loans with a valuation allowance:
Recorded investment	28,897	28,925
Unpaid principal balance	31,655	33,209
Related valuation allowance	2,296	3,128
Average annual recorded investment	25,099	7,829	9,511
Interest income recognized while on impaired status	939	0	0
Impaired loans with no related valuation allowance:
Recorded investment	8,504	7,435
Unpaid principal balance	9,291	11,153
Average annual recorded investment	10,196	29,559	27,778
Interest income recognized while on impaired status	28	1,343	1,005
Total impaired loans:
Recorded investment	37,401	36,360
Unpaid principal balance	40,946	44,362
Related valuation allowance	2,296	3,128
Average annual recorded investment	35,295	37,388	37,289
Interest income recognized while on impaired status	967	1,343	1,005
Commercial real estate
Impaired loans with a valuation allowance:
Recorded investment	28,003	21,318
Unpaid principal balance	34,580	27,558
Related valuation allowance	3,227	2,102
Average annual recorded investment	19,983	5,658	2,918
Interest income recognized while on impaired status	677	0	0
Impaired loans with no related valuation allowance:
Recorded investment	18,080	20,588
Unpaid principal balance	19,861	23,535
Average annual recorded investment	24,658	41,646	50,079
Interest income recognized while on impaired status	245	1,236	1,547
Total impaired loans:
Recorded investment	46,083	41,906
Unpaid principal balance	54,441	51,093
Related valuation allowance	3,227	2,102
Average annual recorded investment	44,641	47,304	52,997
Interest income recognized while on impaired status	922	1,236	1,547
Real estate construction and land development
Impaired loans with a valuation allowance:
Recorded investment	313	177
Unpaid principal balance	313	177
Related valuation allowance	14	4
Average annual recorded investment	175	19	0
Interest income recognized while on impaired status	10	0	0
Impaired loans with no related valuation allowance:
Recorded investment	0	80
Unpaid principal balance	0	80
Average annual recorded investment	78	585	889
Interest income recognized while on impaired status	0	22	25
Total impaired loans:
Recorded investment	313	257
Unpaid principal balance	313	257
Related valuation allowance	14	4
Average annual recorded investment	253	604	889
Interest income recognized while on impaired status	10	22	25
Residential mortgage
Impaired loans with a valuation allowance:
Recorded investment	15,872	20,864
Unpaid principal balance	15,872	20,864
Related valuation allowance	1,487	3,528
Average annual recorded investment	16,390	23,958	20,661
Interest income recognized while on impaired status	538	1,285	1,312
Impaired loans with no related valuation allowance:
Recorded investment	4,902	3,252
Unpaid principal balance	4,902	3,252
Average annual recorded investment	4,622	1,519	6,027
Interest income recognized while on impaired status	38	0	0
Total impaired loans:
Recorded investment	20,774	24,116
Unpaid principal balance	20,774	24,116
Related valuation allowance	1,487	3,528
Average annual recorded investment	21,012	25,477	26,688
Interest income recognized while on impaired status	576	1,285	1,312
Consumer installment
Impaired loans with a valuation allowance:
Recorded investment	966	879
Unpaid principal balance	966	879
Related valuation allowance	120	240
Average annual recorded investment	744	359	0
Interest income recognized while on impaired status	4	0	0
Impaired loans with no related valuation allowance:
Recorded investment	0	0
Unpaid principal balance	0	0
Average annual recorded investment	205	0	448
Interest income recognized while on impaired status	0	0	0
Total impaired loans:
Recorded investment	966	879
Unpaid principal balance	966	879
Related valuation allowance	120	240
Average annual recorded investment	949	359	448
Interest income recognized while on impaired status	4	0	0
Home equity
Impaired loans with a valuation allowance:
Recorded investment	4,570	2,577
Unpaid principal balance	4,570	2,577
Related valuation allowance	858	390
Average annual recorded investment	4,201	1,759	0
Interest income recognized while on impaired status	82	0	0
Impaired loans with no related valuation allowance:
Recorded investment	1,770	774
Unpaid principal balance	1,770	774
Average annual recorded investment	1,392	555	1,872
Interest income recognized while on impaired status	14	0	0
Total impaired loans:
Recorded investment	6,340	3,351
Unpaid principal balance	6,340	3,351
Related valuation allowance	858	390
Average annual recorded investment	5,593	2,314	1,872
Interest income recognized while on impaired status	$ 96	$ 0	$ 0

Loans (Summary of Loan Modifica

Loans (Summary of Loan Modifications by Concession Type) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	112	98	142
Pre- modification recorded investment	$ 10,057	$ 20,819	$ 22,596
Post- modification recorded investment	9,656	20,819	22,594
Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	3,853	15,269	15,206
Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	37	3,393	450
A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	43	0
Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	2,637	364	900
Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 3,129	$ 1,750	$ 6,038
Commercial Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	53	70	77
Pre- modification recorded investment	$ 8,549	$ 19,712	$ 19,347
Post- modification recorded investment	8,343	19,712	19,347
Commercial Loan Portfolio | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	3,049	14,526	12,640
Commercial Loan Portfolio | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	3,393	450
Commercial Loan Portfolio | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	43	0
Commercial Loan Portfolio | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	2,165	0	219
Commercial Loan Portfolio | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 3,129	$ 1,750	$ 6,038
Commercial Loan Portfolio | Commercial
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	36	54	53
Pre- modification recorded investment	$ 6,416	$ 14,853	$ 11,446
Post- modification recorded investment	6,311	14,853	11,446
Commercial Loan Portfolio | Commercial | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	2,308	11,533	6,031
Commercial Loan Portfolio | Commercial | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	1,527	0
Commercial Loan Portfolio | Commercial | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	43	0
Commercial Loan Portfolio | Commercial | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	1,827	0	117
Commercial Loan Portfolio | Commercial | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 2,176	$ 1,750	$ 5,298
Commercial Loan Portfolio | Commercial real estate
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	16	16	21
Pre- modification recorded investment	$ 2,097	$ 4,859	$ 7,196
Post- modification recorded investment	1,997	4,859	7,196
Commercial Loan Portfolio | Commercial real estate | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	706	2,993	5,904
Commercial Loan Portfolio | Commercial real estate | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	1,866	450
Commercial Loan Portfolio | Commercial real estate | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	0	0
Commercial Loan Portfolio | Commercial real estate | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	338	0	102
Commercial Loan Portfolio | Commercial real estate | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 953	$ 0	$ 740
Commercial Loan Portfolio | Real estate construction and land development
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	1		3
Pre- modification recorded investment	$ 36		$ 705
Post- modification recorded investment	35		705
Commercial Loan Portfolio | Real estate construction and land development | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	35		705
Commercial Loan Portfolio | Real estate construction and land development | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0		0
Commercial Loan Portfolio | Real estate construction and land development | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0		0
Commercial Loan Portfolio | Real estate construction and land development | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0		0
Commercial Loan Portfolio | Real estate construction and land development | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 0		$ 0
Consumer Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	59	28	65
Pre- modification recorded investment	$ 1,508	$ 1,107	$ 3,249
Post- modification recorded investment	1,313	1,107	3,247
Consumer Loan Portfolio | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	804	743	2,566
Consumer Loan Portfolio | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	37	0	0
Consumer Loan Portfolio | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	0	0
Consumer Loan Portfolio | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	472	364	681
Consumer Loan Portfolio | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 0	$ 0	$ 0
Consumer Loan Portfolio | Residential mortgage
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	11	4	20
Pre- modification recorded investment	$ 763	$ 477	$ 1,881
Post- modification recorded investment	680	477	1,881
Consumer Loan Portfolio | Residential mortgage | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	297	477	1,246
Consumer Loan Portfolio | Residential mortgage | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	0	0
Consumer Loan Portfolio | Residential mortgage | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	0	0
Consumer Loan Portfolio | Residential mortgage | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	383	0	635
Consumer Loan Portfolio | Residential mortgage | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 0	$ 0	$ 0
Consumer Loan Portfolio | Consumer installment
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	34	14	19
Pre- modification recorded investment	$ 208	$ 87	$ 210
Post- modification recorded investment	192	87	210
Consumer Loan Portfolio | Consumer installment | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	118	87	210
Consumer Loan Portfolio | Consumer installment | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	37	0	0
Consumer Loan Portfolio | Consumer installment | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	0	0
Consumer Loan Portfolio | Consumer installment | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	37	0	0
Consumer Loan Portfolio | Consumer installment | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 0	$ 0	$ 0
Consumer Loan Portfolio | Home equity
Financing Receivable, Modifications [Line Items]
Total number of loans | loan	14	10	26
Pre- modification recorded investment	$ 537	$ 543	$ 1,158
Post- modification recorded investment	441	543	1,156
Consumer Loan Portfolio | Home equity | Principal deferral
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	389	179	1,110
Consumer Loan Portfolio | Home equity | Principal reduction
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	0	0
Consumer Loan Portfolio | Home equity | A/B Note Restructure
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	0	0	0
Consumer Loan Portfolio | Home equity | Interest rate
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	52	364	46
Consumer Loan Portfolio | Home equity | Forbearance agreement
Financing Receivable, Modifications [Line Items]
Post- modification recorded investment	$ 0	$ 0	$ 0

Loans (Summary of TDRs) (Detail

Loans (Summary of TDRs) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Total TDRs	$ 77,888	$ 93,066
Commercial Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total TDRs	58,842	70,785
Consumer Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total TDRs	19,046	22,281
Accruing TDRs
Financing Receivable, Modifications [Line Items]
Total TDRs	48,782	62,535
Accruing TDRs | Commercial Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total TDRs	34,484	45,388
Accruing TDRs | Consumer Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total TDRs	14,298	17,147
Nonaccrual TDRs
Financing Receivable, Modifications [Line Items]
Total TDRs	29,106	30,531
Nonaccrual TDRs | Commercial Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total TDRs	24,358	25,397
Nonaccrual TDRs | Consumer Loan Portfolio
Financing Receivable, Modifications [Line Items]
Total TDRs	$ 4,748	$ 5,134

Loans (Summary of TDRs with a P

Loans (Summary of TDRs with a Payment Default During the Period) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Troubled debt restructurings on financing receivables with defaults payment
Number of loans (in loan) | loan	22	16	9
Principal balance at year end | $	$ 2,051	$ 1,980	$ 2,287
Commercial Loan Portfolio
Troubled debt restructurings on financing receivables with defaults payment
Number of loans (in loan) | loan	5	2	6
Principal balance at year end | $	$ 1,617	$ 1,721	$ 2,222
Consumer Loan Portfolio
Troubled debt restructurings on financing receivables with defaults payment
Number of loans (in loan) | loan	17	14	3
Principal balance at year end | $	$ 434	$ 259	$ 65
Commercial | Commercial Loan Portfolio
Troubled debt restructurings on financing receivables with defaults payment
Number of loans (in loan) | loan	5	0	1
Principal balance at year end | $	$ 1,617	$ 0	$ 1,206
Commercial real estate | Commercial Loan Portfolio
Troubled debt restructurings on financing receivables with defaults payment
Number of loans (in loan) | loan	0	2	5
Principal balance at year end | $	$ 0	$ 1,721	$ 1,016

Loans (Schedule of the Allowanc

Loans (Schedule of the Allowance for Loan Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	$ 78,268	$ 73,328	$ 75,683
Provision (benefit) for loan losses	23,300	14,875	6,500
Charge-offs	(16,867)	(15,302)	(13,501)
Recoveries	7,186	5,367	4,646
Ending balance	91,887	78,268	73,328
Allowance for loan losses
Loans individually evaluated for impairment related to allowance for loan losses				$ 8,002	$ 9,392
Loans collectively evaluated for impairment related to allowance for loan losses				83,885	68,876
Total	78,268	73,328	75,683	91,887	78,268
Loans individually evaluated for impairment related to recorded investment (loan balance)				111,877	106,869
Loans collectively evaluated for impairment related to recorded investment (loan balance)				9,635,552	7,351,532
Total loans				14,155,267	12,990,779
Commercial Loan Portfolio
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	51,201	47,234	44,156
Provision (benefit) for loan losses	19,007	9,788	7,275
Charge-offs	(8,570)	(8,906)	(6,385)
Recoveries	4,495	3,085	2,188
Ending balance	66,133	51,201	47,234
Allowance for loan losses
Loans individually evaluated for impairment related to allowance for loan losses				5,537	5,234
Loans collectively evaluated for impairment related to allowance for loan losses				60,596	45,967
Total	51,201	47,234	44,156	66,133	51,201
Loans individually evaluated for impairment related to recorded investment (loan balance)				83,797	78,523
Loans collectively evaluated for impairment related to recorded investment (loan balance)				5,573,389	4,026,526
Total loans				8,460,527	7,594,212
Consumer Loan Portfolio
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	27,067	26,094	28,803
Provision (benefit) for loan losses	4,293	5,087	1,949
Charge-offs	(8,297)	(6,396)	(7,116)
Recoveries	2,691	2,282	2,458
Ending balance	25,754	27,067	26,094
Allowance for loan losses
Loans individually evaluated for impairment related to allowance for loan losses				2,465	4,158
Loans collectively evaluated for impairment related to allowance for loan losses				23,289	22,909
Total	27,067	26,094	28,803	25,754	27,067
Loans individually evaluated for impairment related to recorded investment (loan balance)				28,080	28,346
Loans collectively evaluated for impairment related to recorded investment (loan balance)				4,062,163	3,325,006
Total loans				5,694,740	5,396,567
Unallocated
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	0	0	2,724
Provision (benefit) for loan losses	0	0	(2,724)
Charge-offs	0	0	0
Recoveries	0	0	0
Ending balance	0	0	0
Allowance for loan losses
Total	$ 0	$ 0	$ 2,724	0	0
Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses
Allowance for loan losses related to loans acquired with deteriorated credit quality				0	0
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)				4,407,838	5,532,378
Receivables Acquired with Deteriorated Credit Quality | Commercial Loan Portfolio
Allowance for loan losses
Allowance for loan losses related to loans acquired with deteriorated credit quality				0	0
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)				2,803,341	3,489,163
Receivables Acquired with Deteriorated Credit Quality | Consumer Loan Portfolio
Allowance for loan losses
Allowance for loan losses related to loans acquired with deteriorated credit quality				0	0
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)				$ 1,604,497	$ 2,043,215

Premises and Equipment (Details

Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	$ 262,387	$ 272,303
Less accumulated depreciation	(135,491)	(127,291)
Premises and equipment, net	126,896	145,012
Net rent expense under operating leases	6,400	3,300	$ 1,700
Closed branch offices transferred to other assets	13,246	4,846	$ 2,692
Land and land improvements
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	31,427	36,185
Buildings
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	130,028	144,155
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	$ 100,932	$ 91,963

Other Real Estate Owned and R99

Other Real Estate Owned and Repossessed Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in other real estate owned
Balance at the beginning of the period	$ 16,812	$ 9,716	$ 13,953
Additions due to acquisitions		13,227	440
Other additions	6,905	9,938	6,957
Net payments received	(1,064)	(1,560)	(45)
Disposals	(12,831)	(13,873)	(10,168)
Write-downs	(1,640)	(636)	(1,421)
Balance at the end of the period	8,182	16,812	9,716
Changes in repossessed assets
Balance at the beginning of the period	375	219	252
Additions due to acquisitions		313	0
Other additions	4,641	3,032	2,372
Net payments received	0	(763)	(22)
Disposals	(4,391)	(2,426)	(2,383)
Write-downs	0	0	0
Balance at the end of the period	$ 625	$ 375	$ 219

Other Real Estate Owned and 100

Other Real Estate Owned and Repossessed Assets (Textuals) (Details) $ in Millions	Dec. 31, 2017USD ($)
Other Real Estate [Abstract]
Other real estate owned and repossessed assets acquired in accordance with ASU 2014-04	$ 0.5
Real estate properties for which formal foreclosure proceedings are in process	$ 4.2

Other Real Estate Owned and 101

Other Real Estate Owned and Repossessed Assets (Income and Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income and expenses related to other real estate owned
Net gain (loss) on sale	$ 3,038	$ 5,325	$ 4,128
Write-downs	(1,640)	(636)	(1,421)
Net operating expenses	(1,981)	(740)	(1,604)
Total	(583)	3,949	1,103
Income and expenses related to repossessed assets
Net gain (loss) on sale	(381)	523	(26)
Write-downs	0	0	0
Net operating expenses	(41)	(60)	(19)
Total	$ (422)	$ 463	$ (45)

Goodwill (Details)

Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2016	Dec. 31, 2015	May 31, 2015	Apr. 01, 2015
Goodwill [Line Items]
Goodwill	$ 1,134,568	$ 1,133,534
Talmer
Goodwill [Line Items]
Goodwill			$ 847,701
Goodwill acquired during period	$ 847,700
Lake Michigan
Goodwill [Line Items]
Goodwill		$ 101,061			$ 101,061
Monarch
Goodwill [Line Items]
Goodwill				$ 5,339		$ 5,339

Loan Servicing Rights (Narrativ

Loan Servicing Rights (Narrative) (Details) $ in Thousands	Dec. 31, 2016USD ($)
Retained Earnings Adjustments [Line Items]
Cumulative effect adjustment of change in accounting policy, net of tax impact	$ 3,659
Retained Earnings [Member]
Retained Earnings Adjustments [Line Items]
Cumulative effect adjustment of change in accounting policy, net of tax impact	$ 3,659

Loan Servicing Rights (LSRs Act

Loan Servicing Rights (LSRs Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Activity for loan servicing rights and the related fair value changes
Fair value, beginning of period	$ 48,085	$ 0
Transfers in based on new accounting policy election	15,891	42,462
Additions from loans sold with servicing retained	8,745	1,030
Changes in fair value due to:
Reductions from pay-offs, pay downs and run-off	2,505	519
Changes in estimates of fair value	(6,375)	5,112
Fair value, end of period	63,841	48,085
Principal balance of loans serviced	7,108,747	5,300,171
Commercial Real Estate
Activity for loan servicing rights and the related fair value changes
Fair value, beginning of period	344	0
Transfers in based on new accounting policy election	0	365
Additions from loans sold with servicing retained	188	0
Changes in fair value due to:
Reductions from pay-offs, pay downs and run-off	(105)	(17)
Changes in estimates of fair value	0	(4)
Fair value, end of period	427	344
Principal balance of loans serviced	40,316	64,756
Mortgage
Activity for loan servicing rights and the related fair value changes
Fair value, beginning of period	47,741	0
Transfers in based on new accounting policy election	15,891	42,097
Additions from loans sold with servicing retained	8,557	1,030
Changes in fair value due to:
Reductions from pay-offs, pay downs and run-off	(2,400)	(502)
Changes in estimates of fair value	(6,375)	5,116
Fair value, end of period	63,414	47,741
Principal balance of loans serviced	$ 7,068,431	$ 5,235,415

Loan Servicing Rights (Carrying

Loan Servicing Rights (Carrying and Fair Value of LSRs) (Details) - Loan Servicing Rights - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Net carrying value of LSRs	$ 10,230	$ 11,122
Fair value of LSRs	15,891	15,542
Valuation allowance	8	0
Loans serviced for others that have servicing rights capitalized	$ 2,074,057	$ 2,082,899

Loan Servicing Rights (Activity

Loan Servicing Rights (Activity for Capitalized LSRs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Activity for Capitalized LSRs
Balance at beginning of period	$ 40,211
Amortization	(6,090)	$ (10,046)	$ (8,444)
Balance at end of period	34,271	40,211
Loan Servicing Rights
Activity for Capitalized LSRs
Balance at beginning of period	$ 10,230	11,122	12,217
Acquired through acquisitions		0	1,284
Additions		3,303	1,476
Amortization		(4,187)	(4,055)
Change in valuation allowance		(8)	200
Balance at end of period		$ 10,230	$ 11,122

Loan Servicing Rights (Assumpti

Loan Servicing Rights (Assumptions Used in Determining Fair Value) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Transfers and Servicing [Abstract]
Loan servicing fee income	$ 18,200,000	$ 8,700,000	$ 5,400,000
Mortgage
Loan servicing rights
Cost to service/per year		66
WA Ancillary income/per year	$ 31	$ 28
WA float range (as a percent)	1.60%	1.00%
Mortgage | Minimum
Loan servicing rights
Prepayment speed (as a percent)		0.00%	0.00%
Cost to service/per year			$ 65
Mortgage | Maximum
Loan servicing rights
Prepayment speed (as a percent)		38.80%	99.80%
Cost to service/per year			$ 90
Mortgage | Weighted Average
Loan servicing rights
Discount rate (as a percent)	10.10%	10.10%

Derivative Instruments and B108

Derivative Instruments and Balance Sheet Offsetting (Notional Amount and Fair Value) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional Amount	$ 2,210,925,000	$ 853,594,000
Gross Derivative Assets	18,681,000	8,215,000
Gross Derivative Liabilities	12,357,000	6,359,000
Credit valuation adjustments for counterparty credit risk	809,000	99,000
Designated as hedging
Derivative [Line Items]
Notional Amount	620,000,000	0
Gross Derivative Assets	5,899,000	0
Gross Derivative Liabilities	0	0
Designated as hedging | Interest rate swaps
Derivative [Line Items]
Notional Amount	620,000,000	0
Gross Derivative Assets	5,899,000	0
Gross Derivative Liabilities	0	0
Not designated as hedging
Derivative [Line Items]
Notional Amount	1,590,925,000	853,594,000
Gross Derivative Assets	12,782,000	8,215,000
Gross Derivative Liabilities	12,357,000	6,359,000
Not designated as hedging | Customer-initiated derivatives
Derivative [Line Items]
Notional Amount	1,365,119,000	600,598,000
Gross Derivative Assets	9,376,000	4,406,000
Gross Derivative Liabilities	10,139,000	4,141,000
Not designated as hedging | Forward contracts related to mortgage loans to be delivered for sale
Derivative [Line Items]
Notional Amount	115,996,000	140,155,000
Gross Derivative Assets	0	635,000
Gross Derivative Liabilities	34,000	0
Not designated as hedging | Interest rate lock commitments
Derivative [Line Items]
Notional Amount	71,003,000	76,034,000
Gross Derivative Assets	1,222,000	956,000
Gross Derivative Liabilities	0	0
Not designated as hedging | Power Equity CD
Derivative [Line Items]
Notional Amount	38,807,000	36,807,000
Gross Derivative Assets	2,184,000	2,218,000
Gross Derivative Liabilities	$ 2,184,000	$ 2,218,000

Other Intangible Assets (Net Ca

Other Intangible Assets (Net Carrying Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other intangible assets:
Total other intangible assets	$ 34,271	$ 40,211
Core deposit intangible assets
Other intangible assets:
Total other intangible assets	34,259	40,211
Non-compete intangible assets
Other intangible assets:
Total other intangible assets	$ 12	$ 0

Derivative Instruments and B110

Derivative Instruments and Balance Sheet Offsetting (Net Gains (Losses) Related to Changes in Fair Value) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative instruments
Net gains (losses) relating to derivative instruments	$ (1,431)	$ (83)	$ 61
Forward contracts related to mortgage loans to be delivered for sale | Net gain (loss) on sale of loans and other mortgage banking revenue
Derivative instruments
Net gains (losses) relating to derivative instruments	(669)	692	193
Interest rate lock commitments | Net gain (loss) on sale of loans and other mortgage banking revenue
Derivative instruments
Net gains (losses) relating to derivative instruments	266	(1,356)	(132)
Customer-initiated derivatives | Other noninterest income
Derivative instruments
Net gains (losses) relating to derivative instruments	$ (1,028)	$ 581	$ 0

Other Intangible Assets (Textua

Other Intangible Assets (Textual) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 6,090	$ 10,046	$ 8,444
Core deposit intangible assets
Finite-Lived Intangible Assets [Line Items]
Remaining weighted-average useful life of intangible assets acquired	7 years 6 months
Amortization of intangible assets	$ 6,000	$ 5,200	$ 4,100

Derivative Instruments and B112

Derivative Instruments and Balance Sheet Offsetting (Balance Sheet Offsetting) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting derivative assets
Gross amounts recognized	$ 18,681	$ 8,215
Offsetting derivative liabilities
Gross amounts recognized	12,357	6,359
Interest rate swaps and customer-initiated derivatives
Offsetting derivative assets
Gross amounts recognized	15,228	4,405
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	15,228	4,405
Gross amounts of assets not offset in the statement of financial position
Financial instruments	0	0
Collateral (received)/posted	0	0
Net Amount	15,228	4,405
Offsetting derivative liabilities
Gross amounts recognized	10,139	4,141
Gross amounts offset in the statements of financial condition	0	0
Net amounts presented in the statements of financial position	10,139	4,141
Gross amounts of liabilities not offset in the statement of financial position
Financial instruments	0	0
Collateral (received)/posted	1,081	2,550
Net Amount	$ 9,058	$ 1,591

Other Intangible Assets (Amorti

Other Intangible Assets (Amortization Expense of Core Deposit Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Net carrying amount	$ 34,271	$ 40,211
Core deposit intangible assets
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Gross carrying amount	59,143	59,143
Accumulated amortization	24,884	18,932
Net carrying amount	$ 34,259	$ 40,211

Derivative Instruments and B114

Derivative Instruments and Balance Sheet Offsetting (Net Gains (Losses) Recorded in Other Comprehensive Income and the Income Statement) (Details) - Designated as hedging - Interest rate swaps $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Derivative [Line Items]
Amount of gain (loss) recognized in other comprehensive income (Effective portion)	$ 4,263
Amount of gain (loss) reclassified from other comprehensive income to interest income or expense (Effective portion)	(1,633)
Amount of gain (loss) recognized in other noninterest income (Ineffective portion)	$ (3)

Other Intangible Assets (Estima

Other Intangible Assets (Estimated Future Amortization Expense) (Details) - Core deposit intangible assets $ in Thousands	Dec. 31, 2017USD ($)
Estimated Future Amortization Expense
2,018	$ 5,703
2,019	5,441
2,020	4,850
2,021	4,471
2,022	$ 4,218

Derivative Instruments and B116

Derivative Instruments and Balance Sheet Offsetting (Narrative) (Details) $ in Millions	Dec. 31, 2017USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Unrealized income on interest rate swaps expected to be reclassified during next twelve months	$ 0.3

Investments in Qualified Aff117

Investments in Qualified Affordable Housing Projects, Federal Historic Projects and New Market Tax Credits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Expense related to qualified affordable housing projects	$ 3.4	$ 2.6	$ 1.3
Remaining investment in qualified affordable housing projects	51.4	29.5
Equity method investments	17.3	10.9
Remaining unfunded equity contributions	48.1	16
Impairment on tax credit projects	7.9	$ 0
Operating expense
Variable Interest Entity [Line Items]
Impairment on tax credit projects	$ 9.3

Commitments, Contingencies a118

Commitments, Contingencies and Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Undisbursed loan commitments	$ 571	$ 578.2
Allowance for credit losses on lending-related commitments	$ 1.2	1.3
Consumer Price Index increase	2.10%
Standby Letters of Credit
Loss Contingencies [Line Items]
Face amount of off-balance sheet liability	$ 187.6	118.9
Commitments to Extend Credit
Loss Contingencies [Line Items]
Face amount of off-balance sheet liability	3,030	2,700
Performance guarantee
Loss Contingencies [Line Items]
Outstanding balance of loans	13.3	16.9
Maximum potential amount of undiscounted future payments	12.8	16.1
Recourse liability	$ 0.2	$ 0.2

Commitments, Contingencies a119

Commitments, Contingencies and Guarantees (Warranties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in the activity related to liability recorded in connection with representations and warranties
Reserve balance at beginning of period	$ 6,459	$ 4,048	$ 3,000
Addition of fair value of representations and warranties due to mergers and acquisitions	0	3,100	1,712
Reserve reduction	(1,095)	(580)	0
Charge-offs	(15)	(109)	(664)
Ending reserve balance	5,349	6,459	4,048
Liability for specific claims				$ 531	$ 730	$ 0
General allowance				4,818	5,729	4,048
Total reserve balance	$ 6,459	$ 4,048	$ 3,000	$ 5,349	$ 6,459	$ 4,048

Commitments, Contingencies a120

Commitments, Contingencies and Guarantees (Operating Leases and Other Noncancelable Contractual Obligations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Future Minimum Lease Payments
2,018	$ 22,973
2,019	21,487
2,020	18,808
2,021	16,794
2,022	20,112
Thereafter	33,775
Total	133,949
Future sublease income	900
Total expense recorded under operating leases and other noncancelable contractual obligations	$ 30,800	$ 20,400	$ 15,600

Deposits (Details)

Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of Deposits
Noninterest-bearing demand	$ 3,725,779	$ 3,341,520
Savings	1,697,762	1,662,115
Interest-bearing demand	2,724,415	2,825,801
Money market accounts	1,957,909	2,033,319
Brokered deposits	453,227	226,429
Other time deposits	3,083,711	2,783,938
Total deposits	13,642,803	12,873,122
Demand deposit overdrafts	5,900	5,000
Time Deposits, $250,000 or More	1,600,000	$ 975,400
Maturities of Time Deposits
2,018	2,168,858
2,019	646,514
2,020	183,101
2,021	134,806
2,022	81,169
Thereafter	2,759
Total	3,217,207
Executive officers, directors, principal shareholders and related interests
Summary of Deposits
Total deposits	$ 10,600

Borrowings (Schedule of Short-

Borrowings (Schedule of Short- and Long-term Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2016
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 372,882	$ 597,847
Long-term borrowings, Weighted Average Rate	1.47%	1.63%
Total short-term and long-term borrowings	$ 2,788,118	$ 1,765,894
Total short-term and long-term borrowings, Weighted Average Rate	1.26%	0.89%
FHLB advances: 1.25% - 1.50% fixed-rate notes | Minimum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	1.25%
FHLB advances: 1.25% - 1.50% fixed-rate notes | Maximum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	1.50%
Federal Home Loan Bank Advances | FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 337,204	$ 438,538
Long-term borrowings, Weighted Average Rate	1.26%	1.24%
Advances payable from Federal Home Loan Banks	$ 337,000	$ 437,800
Purchase accounting premiums	$ 200	700
Federal Home Loan Bank Advances | FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020 | Minimum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	0.92%
Federal Home Loan Bank Advances | FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020 | Maximum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	2.60%
Securities sold under agreements to repurchase | Securities sold under agreements to repurchase
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 0	$ 19,144
Long-term borrowings, Weighted Average Rate	0.00%	3.17%
Advances payable from Federal Home Loan Banks		$ 19,000
Purchase accounting premiums		100
Line of Credit
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 19,963	$ 124,625	$ 125,000
Long-term borrowings, Weighted Average Rate	3.10%	2.52%
Line of Credit | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis spread on variable rate	1.75%
Subordinated Debt Obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 11,425	$ 11,285
Long-term borrowings, Weighted Average Rate	3.69%	3.14%
Purchase accounting discounts	$ 3,600	$ 3,700
Advances payable	$ 15,000	15,000
Subordinated Debt Obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 | Minimum | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis spread on variable rate	1.45%
Subordinated Debt Obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 | Maximum | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis spread on variable rate	2.85%
Subordinated Debt Obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 3.25% due in 2032
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 4,290	$ 4,255
Long-term borrowings, Weighted Average Rate	4.59%	4.25%
Purchase accounting discounts	$ 700	$ 700
Advances payable	$ 5,000	5,000
Subordinated Debt Obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 3.25% due in 2032 | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis spread on variable rate	3.25%
Securities sold under agreements to repurchase
Short Term Borrowings and Long Term Debt [Line Items]
Short-term borrowings, Amount	$ 415,236	$ 343,047
Weighted average interest rate	0.44%	0.16%
Federal Home Loan Bank Advances | FHLB advances: 1.25% - 1.50% fixed-rate notes
Short Term Borrowings and Long Term Debt [Line Items]
Short-term borrowings, Amount	$ 2,000,000	$ 825,000
Weighted average interest rate	1.39%	0.65%

Income Taxes (Provision for Fed

Income Taxes (Provision for Federal Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax expense (benefit)
Federal													$ 14,665	$ 19,144	$ 31,300
State													20	(423)	0
Total current income tax expense													14,685	18,721	31,300
Deferred expense (benefit)
Federal													92,636	23,649	5,700
State													548	442	0
Total deferred income tax expense (benefit)													93,184	24,091	5,700
Change in valuation allowance													(1,089)	(706)	0
Income tax provision	$ 61,234	$ 10,253	$ 23,036	$ 12,257	$ 18,969	$ 2,848	$ 10,532	$ 9,757	$ 10,200	$ 9,600	$ 9,100	$ 8,100	$ 106,780	$ 42,106	$ 37,000

Borrowings (Additional Informat

Borrowings (Additional Information) (Details) - USD ($)	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
FHLB advances		$ 7,360,000,000
Additional borrowing availability through the FHLB		193,500,000
Debt Instrument [Line Items]
Long-term borrowings, Amount		372,882,000	$ 597,847,000
Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 145,000,000
Long-term borrowings, Amount	125,000,000	$ 19,963,000	$ 124,625,000
Repayment of debt	25,000,000
Line of Credit | Term Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	125,000,000
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	20,000,000
Line of Credit Acquired in Merger With Talmer | Line of Credit
Debt Instrument [Line Items]
Repayment of debt	$ 37,500,000

Income Taxes (Effective Tax Rat

Income Taxes (Effective Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount
Tax at statutory rate													$ 89,706	$ 52,548	$ 43,341
Tax-exempt interest income													(9,001)	(5,320)	(3,943)
State taxes, net of federal benefit													369	13	0
Change in valuation allowance													(1,089)	(706)	0
Bank-owned life insurance adjustments													(1,696)	(832)	(124)
Director plan change in control													0	(508)	0
Income tax credits, net													(11,449)	(2,454)	(2,557)
Nondeductible transaction expenses													156	2,100	411
Tax benefits in excess of compensation costs on share-based payments													(5,886)	(2,240)	0
Impact of Tax Cuts and Jobs Act													46,660	0	0
Other, net													(990)	(495)	(128)
Income tax provision	$ 61,234	$ 10,253	$ 23,036	$ 12,257	$ 18,969	$ 2,848	$ 10,532	$ 9,757	$ 10,200	$ 9,600	$ 9,100	$ 8,100	$ 106,780	$ 42,106	$ 37,000
Effective Income Tax Rate, Tax Rate Reconciliation, Percent
Tax at statutory rate													35.00%	35.00%	35.00%
Tax-exempt interest income													(3.50%)	(3.50%)	(3.20%)
State taxes, net of federal benefit													0.10%	0.00%	0.00%
Change in valuation allowance													(0.40%)	(0.50%)	0.00%
Bank-owned life insurance adjustments													(0.70%)	(0.60%)	(0.10%)
Director plan change in control													0.00%	(0.30%)	0.00%
Income tax credits, net													(4.40%)	(1.60%)	(2.10%)
Nondeductible transaction expenses													0.10%	1.40%	0.30%
Tax benefits in excess of compensation costs on share-based payments													(2.30%)	(1.50%)	(0.00%)
Impact of Tax Cuts and Jobs Act													18.20%	0.00%	0.00%
Other, net													(0.40%)	(0.40%)	0.00%
Income tax expense													41.70%	28.00%	29.90%

Income Taxes (Deferred Tax Asse

Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowance for loan losses	$ 20,446	$ 45,763
Acquisition-related fair value adjustments	27,607	54,704
Accrued stock-based compensation	4,082	18,891
Loss and tax credit carry forwards	57,969	76,446
Depreciation	2,954	11,270
Nonaccrual loan interest	6,155	9,465
Accrued expense	9,200	20,858
Other	9,127	15,751
Total deferred tax assets	137,540	253,148
Deferred tax liabilities:
Loan servicing rights	13,446	20,450
Core deposit intangible assets	6,022	11,844
Goodwill	4,076	6,373
Prepaid expenses	7,390	4,873
Other	7,735	2,762
Total deferred tax liabilities	38,669	46,302
Net deferred tax asset before valuation allowance	98,871	206,846
Valuation allowance	(1,150)	(2,239)
Net deferred tax asset	$ 97,721	$ 204,607

Borrowings (Long-term Debt by M

Borrowings (Long-term Debt by Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long-term Debt by Maturity
2,018	$ 147,065
2,019	100,058
2,020	110,044
2,021	0
2,022	0
Thereafter	15,715
Long-term Debt	$ 372,882	$ 597,847

Income Taxes (Textuals) (Detail

Income Taxes (Textuals) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2016	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Tax at statutory rate	35.00%	35.00%	35.00%
Impact of Tax Cuts and Jobs Act	$ 46,660,000	$ 0	$ 0
Impact of Tax Cuts and Jobs Act, revaluation of deferred tax asset	46,000,000
Impact of Tax Cuts and Jobs Act, accelerated amortization	700,000
Net deferred tax assets acquired	151,900,000
Realized Built-in Losses	77,292,000
Valuation allowance for deferred tax assets	1,150,000	2,239,000
Bad debt reserve	91,887,000	78,268,000	$ 73,328,000		$ 75,683,000
Unrecognized tax benefits	0	0
Liabilities accrued for interest or penalties	0	$ 0
Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	64,720,000
Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	25,829,000
Talmer
Operating Loss Carryforwards [Line Items]
Realized Built-in Losses				$ 88,700,000
Valuation allowance for deferred tax assets	1,200,000
Valuation allowance for tax credit carryforward	600,000
Talmer | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses				102,800,000
Tax credit carryforwards				1,000,000
Talmer | Subject to limitations under section 382
Operating Loss Carryforwards [Line Items]
Realized Built-in Losses	0
Valuation allowance for deferred tax assets	600,000
Talmer | Subject to limitations under section 382 | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	0
Talmer | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards				$ 14,900,000
Talmer | Alternative Minimum Tax Credits - no expiration | Subject to limitations under section 382
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	12,473,000
First Place Holdings/First Place Bank | Subject to limitations under section 382
Operating Loss Carryforwards [Line Items]
Realized Built-in Losses	68,356,000
Bad debt reserve	36,000,000
Potential unrecognized tax expense that would impact effective tax rate	7,500,000
First Place Holdings/First Place Bank | Subject to limitations under section 382 | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	0
First Place Holdings/First Place Bank | Alternative Minimum Tax Credits - no expiration | Subject to limitations under section 382
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	2,115,000
Talmer West Bank | Subject to limitations under section 382
Operating Loss Carryforwards [Line Items]
Realized Built-in Losses	8,936,000
Talmer West Bank | Subject to limitations under section 382 | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	47,284,000
Talmer West Bank | Alternative Minimum Tax Credits - no expiration | Subject to limitations under section 382
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 0

Income Taxes (Summary of Loss A

Income Taxes (Summary of Loss Attributes, Section 382 Limitations, and Tax Expiration Periods) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Aug. 31, 2016
Operating Loss Carryforwards [Line Items]
Realized Built-in Losses	$ 77,292
Less amounts not recorded due to Sec 382 Limitation	(5,166)
Valuation Allowance	(1,150)
Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	64,720
Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	3,514
Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	25,829
Talmer
Operating Loss Carryforwards [Line Items]
Realized Built-in Losses		$ 88,700
Estimated recognized built in gain	253,200
Talmer | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses		102,800
Tax Credit Carryforwards		1,000
Talmer | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards		$ 14,900
Monarch
Operating Loss Carryforwards [Line Items]
Estimated recognized built in gain	2,800
Subject to limitations under section 382 | Talmer
Operating Loss Carryforwards [Line Items]
Annual Section 382 limitation-base	34,668
Realized Built-in Losses	0
Less amounts not recorded due to Sec 382 Limitation	0
Valuation Allowance	0
Subject to limitations under section 382 | Talmer | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	0
Subject to limitations under section 382 | Talmer | Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | Talmer | Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	170
Subject to limitations under section 382 | Talmer | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	12,473
Subject to limitations under section 382 | Monarch
Operating Loss Carryforwards [Line Items]
Annual Section 382 limitation-base	673
Realized Built-in Losses	0
Less amounts not recorded due to Sec 382 Limitation	(1,738)
Valuation Allowance	0
Subject to limitations under section 382 | Monarch | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	15,047
Subject to limitations under section 382 | Monarch | Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | Monarch | Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	1,651
Subject to limitations under section 382 | Monarch | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	106
Subject to limitations under section 382 | First Place Holdings/First Place Bank
Operating Loss Carryforwards [Line Items]
Annual Section 382 limitation-base	6,650
Realized Built-in Losses	68,356
Less amounts not recorded due to Sec 382 Limitation	(65)
Valuation Allowance	0
Subject to limitations under section 382 | First Place Holdings/First Place Bank | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	0
Subject to limitations under section 382 | First Place Holdings/First Place Bank | Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | First Place Holdings/First Place Bank | Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	781
Subject to limitations under section 382 | First Place Holdings/First Place Bank | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	2,115
Subject to limitations under section 382 | Talmer West Bank
Operating Loss Carryforwards [Line Items]
Annual Section 382 limitation-base	3,028
Realized Built-in Losses	8,936
Less amounts not recorded due to Sec 382 Limitation	(3,218)
Valuation Allowance	(585)
Subject to limitations under section 382 | Talmer West Bank | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	47,284
Subject to limitations under section 382 | Talmer West Bank | Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | Talmer West Bank | Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | Talmer West Bank | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | First of Huron Corp./Signature Bank
Operating Loss Carryforwards [Line Items]
Annual Section 382 limitation-base	365
Realized Built-in Losses	0
Less amounts not recorded due to Sec 382 Limitation	0
Valuation Allowance	0
Subject to limitations under section 382 | First of Huron Corp./Signature Bank | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	649
Subject to limitations under section 382 | First of Huron Corp./Signature Bank | Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | First of Huron Corp./Signature Bank | Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | First of Huron Corp./Signature Bank | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	303
Subject to limitations under section 382 | From 2009 Ownership change
Operating Loss Carryforwards [Line Items]
Annual Section 382 limitation-base	145
Realized Built-in Losses	0
Less amounts not recorded due to Sec 382 Limitation	(145)
Valuation Allowance	0
Subject to limitations under section 382 | From 2009 Ownership change | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	1,740
Subject to limitations under section 382 | From 2009 Ownership change | Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | From 2009 Ownership change | Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Subject to limitations under section 382 | From 2009 Ownership change | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Not subject to limitations under section 382
Operating Loss Carryforwards [Line Items]
Realized Built-in Losses	0
Less amounts not recorded due to Sec 382 Limitation	0
Valuation Allowance	(565)
Not subject to limitations under section 382 | Federal
Operating Loss Carryforwards [Line Items]
Gross Federal Net Operating Losses	0
Not subject to limitations under section 382 | Gross Capital Losses
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	0
Not subject to limitations under section 382 | Business Tax Credits
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	912
Not subject to limitations under section 382 | Alternative Minimum Tax Credits - no expiration
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	$ 10,832

Share-Based Compensation (Textu

Share-Based Compensation (Textual) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Apr. 26, 2017shares
Share-Based Compensation Plans (Textual) [Abstract]
Share-based compensation expense	$ 17.3	$ 14.7	$ 3.7
Excess tax benefit from share-based compensation	$ 6.1	2.2	0.5
Corporation granted shares of common stock (in shares) | shares	72,537
Common stock available for future grants under share-based compensation plans (in shares) | shares	1,681,101			1,750,000
Cash received from option exercises	$ 3.2	$ 2.7	$ 2.3
Shares issued from exercises (in shares) | shares	621,355	229,055	134,659
Granted after 2012
Share-Based Compensation Plans (Textual) [Abstract]
Stock option vesting period	5 years
Granted prior to 2013
Share-Based Compensation Plans (Textual) [Abstract]
Stock option vesting period	3 years
Stock Options
Share-Based Compensation Plans (Textual) [Abstract]
Stock option expiration period	10 years
Intrinsic value of outstanding in-the-money stock options	$ 26.6	$ 80.4	$ 7.6
Intrinsic value of exercisable in-the-money stock options	$ 21.4
Closing price of common stock (USD per share) | $ / shares	$ 53.47
Unrecognized compensation expense related to share-based compensation	$ 1.9
Unrecognized compensation expense related to share-based compensation, period for recognition	3 years 6 months
Stock Options | Non-vested stock options outstanding
Share-Based Compensation Plans (Textual) [Abstract]
Corporation granted options to purchase common stock (in shares) | shares	132,414	441,167	244,165
Restricted Stock Units
Share-Based Compensation Plans (Textual) [Abstract]
Corporation granted options to purchase restricted stock performance units (in shares) | shares	169,252
Shares issued from exercises (in shares) | shares	75,639
Unrecognized compensation expense related to share-based compensation	$ 9
Unrecognized compensation expense related to share-based compensation, period for recognition	2 years 8 months
Restricted Stock Units | Minimum
Share-Based Compensation Plans (Textual) [Abstract]
Restricted stock performance units eligible to vest as a multiple of number of units granted	0.5
Restricted Stock Units | Maximum
Share-Based Compensation Plans (Textual) [Abstract]
Restricted stock performance units eligible to vest as a multiple of number of units granted	1.5
Restricted Stock Awards
Share-Based Compensation Plans (Textual) [Abstract]
Unrecognized compensation expense related to share-based compensation	$ 2.2
Unrecognized compensation expense related to share-based compensation, period for recognition	1 year 1 month

Share-Based Compensation (Stock

Share-Based Compensation (Stock Options Outstanding Per Range of Exercise Prices) (Details) - Stock Options	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number Outstanding (in shares) | shares	1,110,918
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share)	$ 29.56
Options Outstanding, Weighted Average Contractual Term	6 years 5 months 1 day
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share)	$ 25.99
Options Exercisable, Weighted Average Contractual Term	5 years 6 months 21 days
Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, lower price range limit (USD per share)	$ 11.09
Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, upper price range limit (USD per share)	$ 53.72
$11.09 - 12.80
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number Outstanding (in shares) | shares	32,691
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share)	$ 12.37
Options Outstanding, Weighted Average Contractual Term	2 years 11 months 6 days
Options Exercisable, Number Exercisable (in shares) | shares	32,691
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share)	$ 12.37
Options Exercisable, Weighted Average Contractual Term	2 years 11 months 6 days
$11.09 - 12.80 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, lower price range limit (USD per share)	$ 11.09
$11.09 - 12.80 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, upper price range limit (USD per share)	$ 12.8
$13.20 - 16.24
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number Outstanding (in shares) | shares	136,604
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share)	$ 15.94
Options Outstanding, Weighted Average Contractual Term	4 years 11 months 2 days
Options Exercisable, Number Exercisable (in shares) | shares	136,604
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share)	$ 15.94
Options Exercisable, Weighted Average Contractual Term	4 years 11 months 2 days
$13.20 - 16.24 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, lower price range limit (USD per share)	$ 13.2
$13.20 - 16.24 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, upper price range limit (USD per share)	$ 16.24
$19.97 - 21.10
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number Outstanding (in shares) | shares	49,546
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share)	$ 20.36
Options Outstanding, Weighted Average Contractual Term	2 years 7 months 15 days
Options Exercisable, Number Exercisable (in shares) | shares	49,546
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share)	$ 20.36
Options Exercisable, Weighted Average Contractual Term	2 years 7 months 15 days
$19.97 - 21.10 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, lower price range limit (USD per share)	$ 19.97
$19.97 - 21.10 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, upper price range limit (USD per share)	$ 21.1
$23.78 - 25.14
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number Outstanding (in shares) | shares	232,582
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share)	$ 24.56
Options Outstanding, Weighted Average Contractual Term	4 years 3 months 29 days
Options Exercisable, Number Exercisable (in shares) | shares	232,582
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share)	$ 24.56
Options Exercisable, Weighted Average Contractual Term	4 years 3 months 29 days
$23.78 - 25.14 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, lower price range limit (USD per share)	$ 23.78
$23.78 - 25.14 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, upper price range limit (USD per share)	$ 25.14
$29.45 - 32.81
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number Outstanding (in shares) | shares	537,893
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share)	$ 31.68
Options Outstanding, Weighted Average Contractual Term	7 years 7 months 15 days
Options Exercisable, Number Exercisable (in shares) | shares	290,534
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share)	$ 30.72
Options Exercisable, Weighted Average Contractual Term	7 years 1 month 26 days
$29.45 - 32.81 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, lower price range limit (USD per share)	$ 29.45
$29.45 - 32.81 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, upper price range limit (USD per share)	$ 32.81
$46.95 - 53.72
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number Outstanding (in shares) | shares	121,602
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share)	$ 53.40
Options Outstanding, Weighted Average Contractual Term	9 years 3 months 1 day
Options Exercisable, Number Exercisable (in shares) | shares	38,091
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share)	$ 53.72
Options Exercisable, Weighted Average Contractual Term	9 years 2 months 23 days
$46.95 - 53.72 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, lower price range limit (USD per share)	$ 46.95
$46.95 - 53.72 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price per share, upper price range limit (USD per share)	$ 53.72

Share-Based Compensation (St132

Share-Based Compensation (Stock Option Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted- average grant date fair value per share
Granted, Weighted Average Grant Date Fair Value Per Share (USD per share)	$ 9.94	$ 6.15	$ 8.40
Stock Options | Non-vested stock options outstanding
Number of options
Beginning balance, Number of Options	407,939	479,755	432,199
Granted, Number of Options	132,414	441,167	244,165
Acquired, Number of Options		0	0
Exercised, Number of Options	0	0	0
Vested, Number of Options	(161,751)	(454,360)	(150,224)
Forfeited/expired, Number of Options	(47,732)	(58,623)	(46,385)
Ending balance, Number of Options	330,870	407,939	479,755
Weighted- average exercise price per share
Beginning balance, Weighted Average Exercise Price Per Share (USD per share)	$ 32.81	$ 28.75	$ 26.75
Granted, Weighted Average Exercise Price Per Share (USD per share)	53.43	32.81	30.18
Acquired, Weighted Average Exercise Price Per Share (USD per share)		0	0
Exercised, Weighted Average Exercise Price Per Share (USD per share)	0	0	0
Vested, Weighted Average Exercise Price Per Share (USD per share)	37.73	28.74	25.57
Forfeited/expired, Weighted Average Exercise Price Per Share (USD per share)	37.55	31.10	27.99
Ending balance, Weighted Average Exercise Price Per Share (USD per share)	37.97	32.81	28.75
Weighted- average grant date fair value per share
Beginning balance, Weighted Average Grant Date Fair Value Per Share (USD per share)	6.15	8.49	8.30
Granted, Weighted Average Grant Date Fair Value Per Share (USD per share)	9.94	6.15	8.40
Acquired, Weighted Average Grant Date Fair Value Per Share (USD per share)		0	0
Exercised, Granted, Weighted Average Grant Date Fair Value Per Share (USD per share)	0	0	0
Vested, Granted, Weighted Average Grant Date Fair Value Per Share (USD per share)	7.07	8.49	7.80
Forfeited/expired, Granted, Weighted Average Grant Date Fair Value Per Share (USD per share)	7.03	7.17	8.50
Ending balance, Weighted Average Grant Date Fair Value Per Share (USD per share)	$ 7.09	$ 6.15	$ 8.49
Stock Options | Stock options outstanding
Number of options
Beginning balance, Number of Options	2,453,395	1,054,739	1,037,311
Granted, Number of Options	132,414	441,167	244,165
Acquired, Number of Options		1,466,408	132,883
Exercised, Number of Options	(1,427,159)	(450,296)	(310,985)
Vested, Number of Options	0	0	0
Forfeited/expired, Number of Options	(47,732)	(58,623)	(48,635)
Ending balance, Number of Options	1,110,918	2,453,395	1,054,739
Weighted- average exercise price per share
Beginning balance, Weighted Average Exercise Price Per Share (USD per share)	$ 21.41	$ 25.38	$ 25.90
Granted, Weighted Average Exercise Price Per Share (USD per share)	53.43	32.81	30.18
Acquired, Weighted Average Exercise Price Per Share (USD per share)		15.08	12.93
Exercised, Weighted Average Exercise Price Per Share (USD per share)	17.50	20.02	25.10
Vested, Weighted Average Exercise Price Per Share (USD per share)	0	0	0
Forfeited/expired, Weighted Average Exercise Price Per Share (USD per share)	37.55	31.10	28.18
Ending balance, Weighted Average Exercise Price Per Share (USD per share)	$ 29.56	$ 21.41	$ 25.38
Weighted- average grant date fair value per share
Options Exercisable, Number Exercisable (in shares)	780,048
Exercisable/vested, Weighted Average Exercise Price Per Share (USD per share)	$ 25.99

Share-Based Compensation (Black

Share-Based Compensation (Black-Scholes Pricing Model Assumptions) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assumptions of Black-Scholes option pricing model
Expected dividend yield	3.31%	3.30%	3.50%
Risk-free interest rate	2.05%	1.39%	1.78%
Expected stock price volatility	26.70%	27.90%	39.10%
Expected life of options — in years	6 years	6 years 6 months	7 years
Weighted average fair value of options granted (USD per share)	$ 9.94	$ 6.15	$ 8.40

Share-Based Compensation (Restr

Share-Based Compensation (Restricted Stock Unit Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of units
Converted into shares of common stock, Number of Units	(621,355)	(229,055)	(134,659)
Restricted Stock Units
Number of units
Beginning balance, Number of Units	298,357
Granted, Number of Units	169,252
Converted into shares of common stock, Number of Units	(75,639)
Forfeited/expired, Number of Units	(11,030)
Ending balance, Number of Units	380,940	298,357
Weighted-average grant date fair value per unit
Beginning balance, Weighted Average Grant Date Fair Value Per Share (USD per share)	$ 32.81
Granted, Weighted Average Grant Date Fair Value Per Unit (USD per Unit)	51.93
Converted into shares of common stock, Weighted Average Grant Date Fair Value Per Unit (USD per Unit)	30.73
Forfeited/expired, Weighted Average Grant Date Fair Value Per Unit (USD per Unit)	47.62
Ending balance, Weighted Average Grant Date Fair Value Per Share (USD per share)	$ 41.29	$ 32.81

Share-Based Compensation (Re135

Share-Based Compensation (Restricted Stock Awards Activity) (Details) - Restricted Stock Awards	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Number of awards
Beginning balance, Number of Units | shares	365,891,000
Vested, Number of Units | shares	(277,821,000)
Forfeited, Number of Units | shares	(4,842,000)
Ending balance, Number of Units | shares	83,228,000
Weighted-average acquisition-date fair value
Beginning balance, Weighted Average Grant Date Fair Value Per Share (USD per share) | $ / shares	$ 46.23
Vested (USD per share) | $ / shares	46.23
Forfeited (USD per share) | $ / shares	46.23
Ending balance, Weighted Average Grant Date Fair Value Per Share (USD per share) | $ / shares	$ 46.23

Retirement Plans (401(k) Saving

Retirement Plans (401(k) Savings Plan) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Employer discretionary contribution percent	4.00%
Maximum annual contribution per employee percent	50.00%
Employer matching contribution percent	4.00%
Employer matching contribution amount	$ 2.9	$ 3	$ 1.6
Contribution to 401(k) savings plan	6.2	3.5	3.1
Employer total contribution amount	$ 9.1	$ 6.5	$ 4.7

Retirement Plans (Textual) (Det

Retirement Plans (Textual) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)employeeshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)
Defined Benefit Plan Disclosure [Line Items]
Common Stock, Shares Held by Plan | shares		71,207,114	70,599,133
Dividends paid (in dollars per share)		$ 78,498	$ 49,389	$ 36,918
Multiemployer Plan, Contributions by Employer		0
Multiemployer Plan, Participating Company, Allocation of Plan Liabilities		$ 3,700	2,600
Multiemployer Plan, Company's Asset Participation Level		0.10%
Employer discretionary contribution percent		4.00%
Employer total contribution amount		$ 9,100	6,500	4,700
Contribution to 401(k) savings plan		$ 6,200	3,500	3,100
Maximum annual contribution per employee percent		50.00%
Employer matching contribution percent		4.00%
Employer matching contribution amount		$ 2,900	3,000	1,600
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Number of Employees Covered (in employee) | employee		100
Pension Plan expense		$ (1,495)	73	$ 1,575
Employer contributions		$ 0	$ 0
Discount rate used in determining benefit obligation		3.68%	4.22%	4.55%
Discount rate used in determining expense		4.22%	4.55%	4.15%
Curtailment	$ 100	$ 11,911	$ 0
Pension plan actual asset allocations		100.00%	100.00%
Projected benefit obligation		$ 121,361	$ 123,968	$ 119,873
Accumulated benefit obligation		121,361	115,418
Settlement		$ 0	$ 0	0
Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan actual asset allocations		68.00%	69.00%
Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan actual asset allocations		28.00%	29.00%
Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Pension plan actual asset allocations		4.00%	2.00%
Pension Plan | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Common Stock, Shares Held by Plan | shares		0	210,663
Fair value of common stock		$ 0	$ 11,400
Pension plan actual asset allocations		0.00%	8.60%
SERP
Defined Benefit Plan Disclosure [Line Items]
Pension Plan expense		$ 529	$ 367	$ 417
Employer contributions		$ 0	$ 0
Discount rate used in determining benefit obligation		3.38%	3.63%	4.51%
Discount rate used in determining expense		0.00%	4.51%	4.07%
Curtailment		$ 0	$ 0
Number of employees covered by the pension plan | employee		1
Projected benefit obligation		$ 2,423	2,567	$ 2,160
Accumulated benefit obligation		2,423	2,567
Settlement		(322)	(120)	0
Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Pension Plan expense		(63)	158	$ 278
Employer contributions		$ 198	$ 309
Discount rate used in determining benefit obligation		3.41%	3.79%	4.23%
Discount rate used in determining expense		3.79%	4.23%	3.75%
Curtailment		$ 0	$ 0
Expected health care cost trend rate assumed for 2014		7.50%
Expected ultimate health care cost trend rate in 2020		5.00%
Projected benefit obligation		$ 2,512	2,601	$ 3,247
Accumulated benefit obligation		2,512	2,601
Settlement		$ 0	0	$ 0
Minimum retirement age (years)		50 years
Maximum benefit age of spouse (years)		65 years
Minimum retirement age with twenty-five years of service to be eligible for postretirement benefits (years)		60 years
Minimum years of service for retirees at age sixty to be eligible for postretirement benefits (years)		25 years
Chemical Financial Corporation | Pension Plan | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Dividends paid (in dollars per share)		$ 200	$ 200
Minimum | Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range		40.00%
Minimum | Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range		20.00%
Minimum | Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range		0.00%
Maximum | Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range		70.00%
Maximum | Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range		60.00%
Maximum | Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations range		10.00%
Qualified Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate used in determining expense	3.68%
Nonqualified Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefits owed related to change in control		$ 2,400

Retirement Plans (Changes in th

Retirement Plans (Changes in the Projected Benefit Obligation and Plan Assets) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Projected benefit obligation:
Settlement and other		$ 0
Pension Plan
Projected benefit obligation:
Benefit obligation at beginning of year		123,968	$ 119,873
Service cost		639	1,041	$ 1,021
Interest cost		4,966	5,335	5,242
Settlement and other			0
Net actuarial loss (gain)		10,131	2,684
Benefits paid		(6,432)	(4,965)
Curtailment	$ (100)	(11,911)	0
Benefit obligation at end of year		121,361	123,968	119,873
Fair value of plan assets:
Fair value of plan assets at beginning of year		132,751	126,930
Actual return on plan assets		19,582	10,786
Employer contributions		0	0
Benefits paid		(6,432)	(4,965)
Fair value of plan assets at end of year		145,901	132,751	126,930
Funded (unfunded) status at December 31		24,540	8,783
Accumulated benefit obligation		121,361	115,418
Postretirement Plan
Projected benefit obligation:
Benefit obligation at beginning of year		2,601	3,247
Service cost		5	9	16
Interest cost		94	132	133
Settlement and other			0
Net actuarial loss (gain)		10	(478)
Benefits paid		(198)	(309)
Curtailment		0	0
Benefit obligation at end of year		2,512	2,601	3,247
Fair value of plan assets:
Fair value of plan assets at beginning of year		0	0
Actual return on plan assets		0	0
Employer contributions		198	309
Benefits paid		(198)	(309)
Fair value of plan assets at end of year		0	0	0
Funded (unfunded) status at December 31		(2,512)	(2,601)
Accumulated benefit obligation		2,512	2,601
SERP
Projected benefit obligation:
Benefit obligation at beginning of year		2,567	2,160
Service cost		61	77	70
Interest cost		69	92	85
Settlement and other			(264)
Net actuarial loss (gain)		(274)	536
Benefits paid		0	(34)
Curtailment		0	0
Benefit obligation at end of year		2,423	2,567	2,160
Fair value of plan assets:
Fair value of plan assets at beginning of year		0	0
Actual return on plan assets		0	0
Employer contributions		0	0
Benefits paid		0	0
Fair value of plan assets at end of year		0	0	$ 0
Funded (unfunded) status at December 31		(2,423)	(2,567)
Accumulated benefit obligation		$ 2,423	$ 2,567

Retirement Plans (Weighted-aver

Retirement Plans (Weighted-average rate assumptions of the Pension and Postretirement Plans) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate used in determining benefit obligation — December 31	3.68%	4.22%	4.55%
Discount rate used in determining expense	4.22%	4.55%	4.15%
Discount rate used in determining expense — prior to remeasurement	3.81%	0.00%	0.00%
Expected long-term return on Pension Plan assets	6.75%	6.75%	6.75%
Rate of compensation increase used in determining benefit obligation — December 31	0.00%	3.50%	3.50%
Rate of compensation increase used in determining pension expense	3.50%	3.50%	3.50%
Year 1 increase in cost of postretirement benefits	0.00%	0.00%	0.00%
Postretirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate used in determining benefit obligation — December 31	3.41%	3.79%	4.23%
Discount rate used in determining expense	3.79%	4.23%	3.75%
Discount rate used in determining expense — prior to remeasurement	0.00%	0.00%	0.00%
Expected long-term return on Pension Plan assets	0.00%	0.00%	0.00%
Rate of compensation increase used in determining benefit obligation — December 31	0.00%	0.00%	0.00%
Rate of compensation increase used in determining pension expense	0.00%	0.00%	0.00%
Year 1 increase in cost of postretirement benefits	6.50%	7.00%	7.50%
SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate used in determining benefit obligation — December 31	3.38%	3.63%	4.51%
Discount rate used in determining expense	0.00%	4.51%	4.07%
Discount rate used in determining expense — prior to remeasurement	3.63%	2.87%	0.00%
Expected long-term return on Pension Plan assets	0.00%	0.00%	0.00%
Rate of compensation increase used in determining benefit obligation — December 31	0.00%	3.50%	3.50%
Rate of compensation increase used in determining pension expense	3.50%	3.50%	3.50%
Year 1 increase in cost of postretirement benefits	0.00%	0.00%	0.00%

Retirement Plans (Net Periodic

Retirement Plans (Net Periodic Pension Cost (Income)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan
Service cost	$ 639	$ 1,041	$ 1,021
Interest cost	4,966	5,335	5,242
Expected return on plan assets	(8,938)	(8,562)	(8,645)
Amortization of prior service credit	0	0	(5)
Amortization of net actuarial loss (gain)	1,837	2,259	3,962
Curtailment	1	0	0
Settlement	0	0	0
Net cost (income)	(1,495)	73	1,575
Postretirement Plan
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan
Service cost	5	9	16
Interest cost	94	132	133
Expected return on plan assets	0	0	0
Amortization of prior service credit	0	117	130
Amortization of net actuarial loss (gain)	(162)	(100)	(1)
Curtailment	0	0	0
Settlement	0	0	0
Net cost (income)	(63)	158	278
SERP
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan
Service cost	61	77	70
Interest cost	69	92	85
Expected return on plan assets	0	0	0
Amortization of prior service credit	0	0	0
Amortization of net actuarial loss (gain)	77	78	262
Curtailment	0	0	0
Settlement	322	120	0
Net cost (income)	$ 529	$ 367	$ 417

Retirement Plans (Schedule of E

Retirement Plans (Schedule of Estimated Future Benefit Payments) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Pension Plan
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2,018	$ 6,001
2,019	6,297
2,020	6,392
2,021	6,657
2,022	6,787
2023 - 2027	35,689
Total	67,823
Postretirement Plan
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2,018	230
2,019	230
2,020	231
2,021	230
2,022	227
2023 - 2027	973
Total	2,121
SERP
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2,018	2,063
2,019	22
2,020	22
2,021	22
2,022	22
2023 - 2027	107
Total	$ 2,258

Retirement Plans (Impact of One

Retirement Plans (Impact of One Percentage Point Change in Assumed Health Care and Dental Cost Trend Rates) (Details) - Postretirement Plan $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effect of one percentage point increase on service and interest cost components	$ 8
Effect of one percentage point decrease on service and interest cost components	(8)
Effect of one percentage point increase on postretirement benefit obligation	196
Effect of one percentage point decrease on postretirement benefit obligation	$ (177)

Retirement Plans (Pension Plan

Retirement Plans (Pension Plan Asset Allocations) (Details) - Pension Plan	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	100.00%	100.00%
Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	68.00%	69.00%
Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	28.00%	29.00%
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	4.00%	2.00%

Retirement Plans (Fair Value of

Retirement Plans (Fair Value of Plan Assets by Fair Value Level) (Details) - Pension Plan - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 145,901,000	$ 132,751,000	$ 126,930,000
Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	145,901,000	132,751,000
Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	145,353,000	130,442,000
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	548,000	2,309,000
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,238,000	2,825,000
Cash | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,238,000	2,825,000
Cash | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. large- and mid-cap stocks
Defined Benefit Plan Disclosure [Line Items]
Minimum market capitalization for investments	3,000,000,000
U.S. large- and mid-cap stocks | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	68,909,000	55,389,000
U.S. large- and mid-cap stocks | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	68,909,000	55,389,000
U.S. large- and mid-cap stocks | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. large- and mid-cap stocks | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. small-cap mutual funds | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,377,000	5,687,000
U.S. small-cap mutual funds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,377,000	5,687,000
U.S. small-cap mutual funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. small-cap mutual funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International large-cap mutual funds | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18,341,000	13,701,000
International large-cap mutual funds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18,341,000	13,701,000
International large-cap mutual funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
International large-cap mutual funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Emerging markets mutual funds | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,363,000	5,147,000
Emerging markets mutual funds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,363,000	5,147,000
Emerging markets mutual funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Emerging markets mutual funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Chemical Financial Corporation common stock | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		11,412,000
Chemical Financial Corporation common stock | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		11,412,000
Chemical Financial Corporation common stock | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Chemical Financial Corporation common stock | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
U.S. Treasury and government sponsored agency bonds and notes | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	548,000	806,000
U.S. Treasury and government sponsored agency bonds and notes | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. Treasury and government sponsored agency bonds and notes | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	548,000	806,000
U.S. Treasury and government sponsored agency bonds and notes | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,503,000
Corporate bonds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Corporate bonds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,503,000
Corporate bonds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Mutual funds | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,046,000	36,220,000
Mutual funds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,046,000	36,220,000
Mutual funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other | Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79,000	61,000
Other | Quoted Prices In Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79,000	61,000
Other | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0

Retirement Plans (Changes in Ac

Retirement Plans (Changes in Accumulated Other Comprehensive Income (Loss) Related to Retirement Plans) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax
Reclassification of certain income tax effects	$ 0	[1]
Pension Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	(26,123)
Prior service costs (credits)	0
Net actuarial (income) loss	1,528
Curtailment	7,742
Settlement	0
Reclassification of certain income tax effects	(3,630)
Comprehensive income (loss) adjustment	9,270
Accumulated other comprehensive income (loss) at end of year	(20,483)
Postretirement Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	724
Prior service costs (credits)	0
Net actuarial (income) loss	(112)
Curtailment	0
Settlement	0
Reclassification of certain income tax effects	132
Comprehensive income (loss) adjustment	(112)
Accumulated other comprehensive income (loss) at end of year	744
SERP
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	(495)
Prior service costs (credits)	0
Net actuarial (income) loss	229
Curtailment	0
Settlement	209
Reclassification of certain income tax effects	(12)
Comprehensive income (loss) adjustment	438
Accumulated other comprehensive income (loss) at end of year	(69)
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	(25,894)
Prior service costs (credits)	0
Net actuarial (income) loss	1,645
Curtailment	7,742
Settlement	209
Reclassification of certain income tax effects	(3,510)
Comprehensive income (loss) adjustment	9,596
Accumulated other comprehensive income (loss) at end of year	$ (19,808)
[1]	The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, refer to Note 1 for further details on the adoption.

Retirement Plans (Income (Loss)

Retirement Plans (Income (Loss) Estimated to be Amortized from Accumulated Other Comprehensive Income (Loss) into Net Periodic Cost) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	$ 0
Net gain (loss)	(448)
Total	(448)
Pension Plan
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	0
Net gain (loss)	(561)
Total	(561)
Postretirement Plan
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	0
Net gain (loss)	113
Total	113
SERP
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Twelve Months
Prior service (costs) credits	0
Net gain (loss)	0
Total	$ 0

Equity (Details)

Equity (Details) - shares	12 Months Ended
	Dec. 31, 2017	Apr. 26, 2017	Apr. 25, 2017	Dec. 31, 2016	Jul. 19, 2016	Jul. 18, 2016	Apr. 20, 2015	Apr. 20, 2009	Jan. 31, 2008
Class of Stock [Line Items]
Preferred stock, shares authorized	2,000,000			2,000,000			2,000,000	200,000
Preferred stock, shares issued	0			0
Preferred stock, shares outstanding	0
Common sock, shares authorized	135,000,000	135,000,000	100,000,000	100,000,000	100,000,000	60,000,000
Common Stock
Class of Stock [Line Items]
Stock repurchased during the period	0
Number of remaining shares authorized to be repurchased	500,000
Common Stock
Class of Stock [Line Items]
Number of shares authorized to be repurchased									500,000

Regulatory Capital and Reser148

Regulatory Capital and Reserve Requirements (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 23, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Minimum average regulatory cash reserve balance		$ 71,700											$ 71,700	$ 52,300
Leverage Ratio:
Cash dividends declared per share (in dollars per share)		$ 0.27	$ 0.28	$ 0.27	$ 0.27	$ 0.27	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.24	$ 0.24	$ 1.10	$ 1.06	$ 1
Subsequent Event
Leverage Ratio:
Cash dividends declared per share (in dollars per share)	$ 0.28
Chemical Financial Corporation
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk weighted assets		$ 14,740,000											$ 14,740,000	$ 13,420,000
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount		$ 1,614,046											$ 1,614,046	$ 1,543,018
Actual, Ratio		11.00%											11.00%	11.50%
Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 1,179,076											$ 1,179,076	$ 1,073,431
Minimum Required for Capital Adequacy Purposes, Ratio		8.00%											8.00%	8.00%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 1,363,307											$ 1,363,307	$ 1,157,293
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		9.30%											9.30%	8.60%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount		$ 1,498,463											$ 1,498,463	$ 1,441,209
Actual, Ratio		10.20%											10.20%	10.70%
Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 884,307											$ 884,307	$ 805,073
Minimum Required for Capital Adequacy Purposes, Ratio		6.00%											6.00%	6.00%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 1,068,538											$ 1,068,538	$ 888,935
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		7.30%											7.30%	6.60%
Common Equity Tier 1 Capital to Risk-Weighted Assets
Actual, Capital Amount		$ 1,498,463											$ 1,498,463	$ 1,441,209
Minimum Required for Capital Adequacy Purposes, Capital Amount		10.20%											10.20%	10.70%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount		$ 663,230											$ 663,230	$ 603,805
Actual, Ratio		4.50%											4.50%	4.50%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 847,461											$ 847,461	$ 687,667
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		5.80%											5.80%	5.10%
Leverage Ratio:
Actual, Capital Amount		$ 1,498,463											$ 1,498,463	$ 1,441,209
Actual, Ratio		8.30%											8.30%	9.00%
Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 720,890											$ 720,890	$ 643,603
Minimum Required for Capital Adequacy Purposes, Ratio		4.00%											4.00%	4.00%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 720,890											$ 720,890	$ 643,603
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		4.00%											4.00%	4.00%
Cash dividends from subsidiaries													$ 165,000	$ 110,450	$ 56,860
Chemical Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk weighted assets		$ 14,700,000											14,700,000	13,360,000
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount		$ 1,613,087											$ 1,613,087	$ 1,608,980
Actual, Ratio		11.00%											11.00%	12.00%
Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 1,176,361											$ 1,176,361	$ 1,068,560
Minimum Required for Capital Adequacy Purposes, Ratio		8.00%											8.00%	8.00%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 1,360,167											$ 1,360,167	$ 1,152,041
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		9.30%											9.30%	8.60%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount		$ 1,470,451											$ 1,470,451	$ 1,335,700
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio		10.00%											10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount		$ 1,513,219											$ 1,513,219	$ 1,522,711
Actual, Ratio		10.30%											10.30%	11.40%
Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 882,271											$ 882,271	$ 801,420
Minimum Required for Capital Adequacy Purposes, Ratio		6.00%											6.00%	6.00%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 1,066,077											$ 1,066,077	$ 884,901
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		7.30%											7.30%	6.60%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount		$ 1,176,361											$ 1,176,361	$ 1,068,560
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio		8.00%											8.00%	8.00%
Common Equity Tier 1 Capital to Risk-Weighted Assets
Actual, Capital Amount		$ 1,513,219											$ 1,513,219	$ 1,522,711
Minimum Required for Capital Adequacy Purposes, Capital Amount		10.30%											10.30%	11.40%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount		$ 661,703											$ 661,703	$ 601,065
Actual, Ratio		4.50%											4.50%	4.50%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 845,509											$ 845,509	$ 684,546
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		5.80%											5.80%	5.10%
Minimum Required for Capital Adequacy Purposes, Ratio		$ 955,793											$ 955,793	$ 868,205
Required to be Well Capital Under Prompt Corrective Action Regulations, Ratio		6.50%											6.50%	6.50%
Leverage Ratio:
Actual, Capital Amount		$ 1,513,219											$ 1,513,219	$ 1,522,711
Actual, Ratio		8.40%											8.40%	9.50%
Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 720,043											$ 720,043	$ 641,457
Minimum Required for Capital Adequacy Purposes, Ratio		4.00%											4.00%	4.00%
For Capital Adequacy Purposes Plus Capital Conservation Buffer Amount		$ 720,043											$ 720,043	$ 641,457
For Capital Adequacy Purposes Plus Capital Conservation Buffer Ratio		4.00%											4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount		$ 900,053											$ 900,053	$ 801,822
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio		5.00%											5.00%	5.00%

Parent Company Only Financia149

Parent Company Only Financial Statements (Financial Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Premises and equipment	$ 126,896	$ 145,012
Goodwill	1,134,568	1,133,534
Other assets	709,154	650,973
Total assets	19,280,873	17,355,179
Liabilities and Equity [Abstract]
Other liabilities	181,203	134,637
Total liabilities	16,612,124	14,773,653
Shareholders' equity	2,668,749	2,581,526	$ 1,015,974	$ 797,133
Total liabilities and shareholders' equity	19,280,873	17,355,179
Chemical Financial Corporation
Assets
Cash at subsidiary bank	5,761	16,851
Investment in subsidiaries	2,673,858	2,654,458
Premises and equipment	3,931	4,051
Goodwill	1,092	1,092
Deferred tax asset	7,203	30,715
Other assets	31,459	32,869
Total assets	2,723,304	2,740,036
Liabilities and Equity [Abstract]
Other liabilities	18,877	18,345
Non-revolving line-of-credit	19,963	124,625
Subordinated debentures	15,715	15,540
Total liabilities	54,555	158,510
Shareholders' equity	2,668,749	2,581,526
Total liabilities and shareholders' equity	$ 2,723,304	$ 2,740,036

Parent Company Only Financia150

Parent Company Only Financial Statements (Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Other income													$ 25,918	$ 11,988	$ 1,907
Interest expense	$ 23,257	$ 21,316	$ 17,185	$ 12,799	$ 11,969	$ 6,753	$ 5,442	$ 5,134	$ 5,153	$ 5,234	$ 3,944	$ 3,450	74,557	29,298	17,781
Operating expenses	100,022	119,539	98,237	104,196	114,302	106,144	59,085	58,887	57,824	58,265	56,785	51,020	421,994	338,418	223,894
Income tax benefit	(61,234)	(10,253)	(23,036)	(12,257)	(18,969)	(2,848)	(10,532)	(9,757)	(10,200)	(9,600)	(9,100)	(8,100)	(106,780)	(42,106)	(37,000)
Net income	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	149,523	108,032	86,830
Chemical Financial Corporation
Condensed Financial Statements, Captions [Line Items]
Cash dividends from subsidiaries													165,000	110,450	56,860
Other income													921	151	144
Total income													165,921	110,601	57,004
Interest expense													3,076	1,816	761
Operating expenses													23,298	30,589	7,794
Total expenses													26,374	32,405	8,555
Income before income taxes and equity in undistributed net income of subsidiaries													139,547	78,196	48,449
Income tax benefit													12,670	11,378	2,582
Equity in undistributed net (loss) income of subsidiaries													(2,694)	18,458	35,799
Net income													$ 149,523	$ 108,032	$ 86,830

Parent Company Only Financia151

Parent Company Only Financial Statements (Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows From Operating Activities
Net Income	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	$ 149,523	$ 108,032	$ 86,830
Share-based compensation expense													17,346	13,452	3,478
Depreciation of premises and equipment													17,722	13,270	11,028
Net cash from operating activities													275,009	280,578	103,049
Cash Flows From Investing Activities
Purchases of premises and equipment, net													(12,852)	(18,098)	(8,527)
Net cash used in investing activities													(1,983,079)	(542,946)	(408,784)
Cash Flows From Financing Activities
Cash dividends paid													(78,498)	(49,389)	(36,918)
Repayments of other borrowings													(224,850)	(351,018)	(6,000)
Proceeds from issuance of other borrowings													0	375,000	125,000
Proceeds from directors' stock purchase plan and exercise of stock options													3,991	1,572	2,473
Cash paid for payroll taxes upon conversion of restricted stock units													(27,854)	(1,065)	(571)
Net cash from financing activities													1,689,659	497,981	361,504
Net increase (decrease) in cash and cash equivalents													(18,411)	235,613	55,769
Cash and cash equivalents at beginning of year				474,402				238,789				183,020	474,402	238,789	183,020
Cash and cash equivalents at end of year	455,991				474,402				238,789				455,991	474,402	238,789
Business combinations:
Fair value of tangible assets acquired (noncash)													420	6,371,781	1,282,420
Liabilities assumed													1,454	6,100,901	1,258,051
Common stock and stock options issued													0	1,504,811	159,904
Chemical Financial Corporation
Cash Flows From Operating Activities
Net Income													149,523	108,032	86,830
Share-based compensation expense													17,346	13,452	3,478
Depreciation of premises and equipment													408	355	318
Equity in undistributed net loss (income) of subsidiaries													2,694	(18,458)	(35,799)
Net decrease in other assets													1,410	9,752	2,873
Net increase (decrease) in other liabilities													25,178	(11,830)	(19,033)
Net cash from operating activities													196,559	101,303	38,667
Cash Flows From Investing Activities
Cash acquired, net of cash paid, in business combinations													0	(107,622)	(45,267)
Purchases of premises and equipment, net													(288)	(774)	(320)
Net cash used in investing activities													(288)	(108,396)	(45,587)
Cash Flows From Financing Activities
Cash dividends paid													(78,498)	(49,389)	(36,918)
Proceeds from issuance of common stock, net of issuance costs													0	0	0
Repayment of subordinated debt obligations													0	(18,558)	0
Repayments of other borrowings													(105,000)	(62,500)	0
Proceeds from issuance of other borrowings													0	125,000	25,000
Proceeds from directors' stock purchase plan and exercise of stock options													3,991	1,572	2,473
Cash paid for payroll taxes upon conversion of restricted stock units													(27,854)	(1,065)	(571)
Net cash from financing activities													(207,361)	(4,940)	(10,016)
Net increase (decrease) in cash and cash equivalents													(11,090)	(12,033)	(16,936)
Cash and cash equivalents at beginning of year				$ 16,851				$ 28,884				$ 45,820	16,851	28,884	45,820
Cash and cash equivalents at end of year	$ 5,761				$ 16,851				$ 28,884				5,761	16,851	28,884
Business combinations:
Fair value of tangible assets acquired (noncash)													0	46,898	10,304
Liabilities assumed													0	58,309	42,019
Common stock and stock options issued													$ 0	$ 1,504,811	$ 159,904

Earnings Per Common Share (Deta

Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net Income	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	$ 149,523	$ 108,032	$ 86,830
Net income allocated to participating securities													495	166	0
Net income allocated to common shareholders													$ 149,028	$ 107,866	$ 86,830
Weighted average common shares - issued (in shares)													71,103,000	49,091,000	36,081,000
Average unvested restricted share awards (in shares)													(238,000)	(139,000)	0
Weighted average common shares outstanding - basic (in shares)													70,865,000	48,952,000	36,081,000
Effect of dilutive securities
Weighted average common stock equivalents (in shares)													648,000	651,000	272,000
Weighted average common shares outstanding - diluted (in shares)													71,513,000	49,603,000	36,353,000
EPS available to common shareholders
Basic earnings per common share (usd per share)	$ 0.13	$ 0.57	$ 0.73	$ 0.67	$ 0.67	$ 0.23	$ 0.67	$ 0.61	$ 0.67	$ 0.64	$ 0.54	$ 0.54	$ 2.11	$ 2.21	$ 2.41
Diluted earnings per common share (usd per share)	$ 0.13	$ 0.56	$ 0.73	$ 0.67	$ 0.66	$ 0.23	$ 0.67	$ 0.60	$ 0.66	$ 0.64	$ 0.54	$ 0.54	2.08	2.17	2.39
Schedule Of Earnings Per Share By Common Class [Line Items]
Average stock valuation (usd per share)													$ 50.26	$ 40.58	$ 32.17
Stock Option
Schedule Of Earnings Per Share By Common Class [Line Items]
Average number of exercisable employee stock option awards that were not included in the computation of diluted earnings per common share (in shares)													107,272	0	54,771

Accumulated Other Comprehens153

Accumulated Other Comprehensive Loss (Changes in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		$ 2,581,526	$ 1,015,974	$ 797,133
Other comprehensive loss before reclassifications		12,054	(12,399)	1,174
Amounts reclassified from accumulated other comprehensive income		7,002	1,395	2,247
Net current period other comprehensive income (loss)		19,056	(11,004)	3,421
Reclassification of certain income tax effects	[1]	0
Ending balance		2,668,749	2,581,526	1,015,974
Total
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		(40,036)	(29,032)	(32,453)
Reclassification of certain income tax effects	[1]	4,518
Ending balance		(25,498)	(40,036)	(29,032)
Unrealized gains (losses) on securities available-for-sale, net of tax
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		(14,142)	(1,888)	(210)
Other comprehensive loss before reclassifications		826	(12,170)	(1,269)
Amounts reclassified from accumulated other comprehensive income		4,802	(84)	(409)
Net current period other comprehensive income (loss)		5,628	(12,254)	(1,678)
Reclassification of certain income tax effects		1,834
Ending balance		(10,348)	(14,142)	(1,888)
Defined Benefit Pension Plans
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		(25,894)	(27,144)	(32,243)
Other comprehensive loss before reclassifications		8,457	(229)	2,443
Amounts reclassified from accumulated other comprehensive income		1,139	1,479	2,656
Net current period other comprehensive income (loss)		9,596	1,250	5,099
Reclassification of certain income tax effects		3,510
Ending balance		(19,808)	(25,894)	(27,144)
Unrealized gains (losses) on cash flow hedges, net of tax
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Beginning balance		0	0	0
Other comprehensive loss before reclassifications		2,771	0	0
Amounts reclassified from accumulated other comprehensive income		1,061	0	0
Net current period other comprehensive income (loss)		3,832	0	0
Reclassification of certain income tax effects		(826)
Ending balance		4,658	$ 0	$ 0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)
Components of accumulated other comprehensive income (loss), net of related tax benefit/expense
Reclassification of certain income tax effects		$ 4,518
[1]	The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, refer to Note 1 for further details on the adoption.

Accumulated Other Comprehens154

Accumulated Other Comprehensive Loss (Reclassifications Out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense)/benefit	$ (61,234)	$ (10,253)	$ (23,036)	$ (12,257)	$ (18,969)	$ (2,848)	$ (10,532)	$ (9,757)	$ (10,200)	$ (9,600)	$ (9,100)	$ (8,100)	$ (106,780)	$ (42,106)	$ (37,000)
Net (loss) gain on sale of investment securities													(7,388)	129	630
Net Income													(7,002)	(1,395)	(2,247)
Interest on short-term borrowings													20,321	1,660	453
Net Income	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	149,523	108,032	86,830
Unrealized gains (losses) on securities available-for-sale, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income													(4,802)	84	409
Unrealized gains (losses) on securities available-for-sale, net of tax | Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains and losses on available-for-sale securities													(7,388)	129	630
Income tax (expense)/benefit													2,586	(45)	(221)
Net Income													(4,802)	84	409
Amortization of defined benefit pension plan items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries, wages and employee benefits (operating expenses)													(1,752)	(2,276)	(4,086)
Income tax (expense)/benefit													613	797	1,430
Net Income													(1,139)	(1,479)	(2,656)
Unrealized gains (losses) on cash flow hedges, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income													(1,061)	0	0
Unrealized gains (losses) on cash flow hedges, net of tax | Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense)/benefit													(572)	0	0
Interest on short-term borrowings													1,633	0	0
Net Income													$ 1,061	$ 0	$ 0

Summary of Quarterly Stateme155

Summary of Quarterly Statements of Income (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information [Abstract]
Interest income	$ 169,162	$ 164,944	$ 155,133	$ 142,896	$ 144,416	$ 103,562	$ 82,937	$ 79,464	$ 80,629	$ 78,851	$ 69,679	$ 62,630	$ 632,135	$ 410,379	$ 291,789
Interest expense	23,257	21,316	17,185	12,799	11,969	6,753	5,442	5,134	5,153	5,234	3,944	3,450	74,557	29,298	17,781
Net interest income	145,905	143,628	137,948	130,097	132,447	96,809	77,495	74,330	75,476	73,617	65,735	59,180	557,578	381,081	274,008
Provision for loan losses	7,522	5,499	6,229	4,050	6,272	4,103	3,000	1,500	2,000	1,500	1,500	1,500	23,300	14,875	6,500
Noninterest income	32,319	32,122	41,568	38,010	54,264	27,770	20,897	19,419	20,052	20,215	20,674	19,275	144,019	122,350	80,216
Operating expenses	100,022	119,539	98,237	104,196	114,302	106,144	59,085	58,887	57,824	58,265	56,785	51,020	421,994	338,418	223,894
Income before income taxes	70,680	50,712	75,050	59,861	66,137	14,332	36,307	33,362	35,704	34,067	28,124	25,935	256,303	150,138	123,830
Income tax expense	61,234	10,253	23,036	12,257	18,969	2,848	10,532	9,757	10,200	9,600	9,100	8,100	106,780	42,106	37,000
Net income	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	$ 149,523	$ 108,032	$ 86,830
Basic earnings per common share (usd per share)	$ 0.13	$ 0.57	$ 0.73	$ 0.67	$ 0.67	$ 0.23	$ 0.67	$ 0.61	$ 0.67	$ 0.64	$ 0.54	$ 0.54	$ 2.11	$ 2.21	$ 2.41
Diluted earnings per common share (usd per share)	0.13	0.56	0.73	0.67	$ 0.66	0.23	0.67	0.60	0.66	0.64	0.54	0.54	2.08	2.17	2.39
Cash dividends declared per share (in dollars per share)	$ 0.27	$ 0.28	$ 0.27	$ 0.27		$ 0.27	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.24	$ 0.24	$ 1.10	$ 1.06	$ 1