TCF Financial 10-Q 30 Apr 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 17, 2015
Entity Information [Line Items]
Entity Registrant Name	CHEMICAL FINANCIAL CORP
Entity Central Index Key	19612
Document Type	10-Q
Document Period End Date	31-Mar-15
Amendment Flag	FALSE
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		33,711,700

Consolidated_Statements_of_Fin

Consolidated Statements of Financial Position (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Cash and cash equivalents:
Cash and cash due from banks	$121,796	$144,892	$122,288
Interest-bearing deposits with the Federal Reserve Bank and other banks	272,142	38,128	260,097
Total cash and cash equivalents	393,938	183,020	382,385
Investment securities:
Available-for-sale, at fair value	680,644	748,864	657,818
Held-to-maturity (fair value - $380,176 at March 31, 2015, $315,740 at December 31, 2014 and $272,407 at March 31, 2014)	381,450	316,413	278,099
Total investment securities	1,062,094	1,065,277	935,917
Loans held-for-sale, at fair value	9,675	9,128	3,814
Loans	5,702,874	5,688,230	4,753,289
Allowance for loan losses	-75,256	-75,683	-78,473
Net loans	5,627,618	5,612,547	4,674,816
Premises and equipment (net of accumulated depreciation of $111,270 at March 31, 2015, $108,826 at December 31, 2014 and $102,163 at March 31, 2014)	96,486	97,496	74,779
Goodwill	180,128	180,128	120,164
Other intangible assets	31,655	33,080	12,872
Interest receivable and other assets	150,041	141,467	133,581
Total Assets	7,551,635	7,322,143	6,338,328
Deposits:
Noninterest-bearing	1,614,319	1,591,661	1,219,081
Interest-bearing	4,706,034	4,487,310	4,012,212
Total deposits	6,320,353	6,078,971	5,231,293
Interest payable and other liabilities	48,545	56,572	40,209
Short-term borrowings	372,236	389,467	361,231
Total liabilities	6,741,134	6,525,010	5,632,733
Shareholders’ equity:
Preferred stock, no par value: Authorized - 200,000 shares, none issued	0	0	0
Issued and outstanding — 32,847,063 shares at March 31, 2015, 32,774,420 shares at December 31, 2014 and 29,865,841 shares at March 31, 2014	32,847	32,774	29,866
Additional paid-in capital	565,851	565,166	489,045
Retained earnings	241,582	231,646	205,985
Accumulated other comprehensive loss	-29,779	-32,453	-19,301
Total shareholders’ equity	810,501	797,133	705,595
Total Liabilities and Shareholders’ Equity	$7,551,635	$7,322,143	$6,338,328

Consolidated_Statements_of_Fin1

Consolidated Statements of Financial Position (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, except Share data, unless otherwise specified
Held-to-maturity, fair value	$380,176	$315,740	$272,407
Accumulated depreciation of premises and equipment	$111,270	$108,826	$102,163
Preferred stock, no par value
Preferred stock, shares authorized	200,000	200,000	200,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$1	$1	$1
Common stock, shares authorized	45,000,000	45,000,000	45,000,000
Common stock, shares issued	32,847,063	32,774,420	29,865,841
Common stock, shares outstanding	32,847,063	32,774,420	29,865,841

Consolidated_Statements_of_Inc

Consolidated Statements of Income (Unaudited) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Interest Income
Interest and fees on loans	$58,097	$49,195
Interest on investment securities:
Taxable	2,307	2,383
Tax-exempt	1,906	1,704
Dividends on nonmarketable equity securities	198	238
Interest on deposits with the Federal Reserve Bank and other banks	122	125
Total interest income	62,630	53,645
Interest Expense
Interest on deposits	3,352	3,745
Interest on short-term borrowings	98	121
Total interest expense	3,450	3,866
Net Interest Income	59,180	49,779
Provision for loan losses	1,500	1,600
Net interest income after provision for loan losses	57,680	48,179
Noninterest Income
Service charges and fees on deposit accounts	5,916	4,930
Wealth management revenue	5,071	3,631
Other charges and fees for customer services	5,990	4,194
Mortgage banking revenue	1,403	794
Gain on sale of investment securities	579	0
Other	316	167
Total noninterest income	19,275	13,716
Operating Expenses
Salaries, wages and employee benefits	29,268	24,184
Occupancy	4,426	4,374
Equipment and software	4,738	3,461
Other	12,588	10,163
Total operating expenses	51,020	42,182
Income before income taxes	25,935	19,713
Federal income tax expense	8,100	5,900
Net Income	$17,835	$13,813
Net Income Per Common Share:
Basic (in dollars per share)	$0.54	$0.46
Diluted (in dollars per share)	$0.54	$0.46
Cash Dividends Declared Per Common Share (dollars per share)	$0.24	$0.23

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net income	$17,835	$13,813
Other comprehensive income (loss), net of tax:
Net unrealized gains on investment securities available-for-sale, net of tax expense of $1,262 and $857 for the three months ended March 31, 2015 and 2014, respectively	2,344	1,593
Reclassification adjustment for realized gain on sale of investment securities available-for-sale included in net income, net of tax expense of $203 for the three months ended March 31, 2015	-376	0
Adjustment for pension and other postretirement benefits, net of tax expense (benefit) of $381 and $(201) for the three months ended March 31, 2015 and 2014, respectively	706	-374
Total other comprehensive income (loss), net of tax	2,674	1,219
Comprehensive income	$20,509	$15,032

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Tax expense (benefit) on net unrealized gains (losses) on investment securities available-for-sale	$1,262	$857
Tax expense (benefit) on reclassification adjustment for realized gains on sale of investment securities available-for-sale	-203	0
Tax expense (benefit) on adjustment for pension and other postretirement benefits	$381	($201)

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (USD $)	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
In Thousands, unless otherwise specified
Beginning Balance at Dec. 31, 2013	$696,500	$29,790	$488,177	$199,053	($20,520)
Changes in Stockholders' Equity [Roll Forward]
Comprehensive income	15,032			13,813	1,219
Cash dividends declared per share: $0.24 and $0.23 per share for the three months ended March 31, 2015 and March 31, 2014, respectively	-6,881			-6,881
Stock issued - stock options	557	27	530
Shares issued – directors’ stock plans	310	12	298
Shares issued – restricted stock units	-477	36	-513
Share-based compensation	554	1	553
Ending Balance at Mar. 31, 2014	705,595	29,866	489,045	205,985	-19,301
Beginning Balance at Dec. 31, 2014	797,133	32,774	565,166	231,646	-32,453
Changes in Stockholders' Equity [Roll Forward]
Comprehensive income	20,509			17,835	2,674
Cash dividends declared per share: $0.24 and $0.23 per share for the three months ended March 31, 2015 and March 31, 2014, respectively	-7,899			-7,899
Stock issued - stock options	131	13	118
Shares issued – directors’ stock plans	316	11	305
Shares issued – restricted stock units	-444	48	-492
Share-based compensation	755	1	754
Ending Balance at Mar. 31, 2015	$810,501	$32,847	$565,851	$241,582	($29,779)

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash dividends declared per share	$0.24	$0.23

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating Activities
Net income	$17,835	$13,813
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	1,500	1,600
Gains on sales of loans	-1,589	-647
Proceeds from sales of loans	54,280	22,080
Loans originated for sale	-53,238	-20,028
Net gains from sales/writedowns of other real estate and repossessed assets	-570	-379
Depreciation of premises and equipment	2,479	2,119
Amortization of intangible assets	1,825	695
Gain on sale of investment securities	-579	0
Net amortization of premiums and discounts on investment securities	1,373	1,093
Share-based compensation expense	755	554
Net increase in interest receivable and other assets	-9,562	-1,319
Net increase (decrease) in interest payable and other liabilities	-7,038	1,239
Net cash provided by operating activities	7,471	20,820
Investment securities – available-for-sale:
Proceeds from sales	13,172	0
Proceeds from maturities, calls and principal reductions	57,449	28,426
Investment securities – held-to-maturity:
Proceeds from maturities, calls and principal reductions	7,542	31,798
Purchases	-72,748	-36,309
Net increase in loans	-20,233	-109,965
Proceeds from sales of other real estate and repossessed assets	3,693	2,197
Purchases of premises and equipment, net of disposals	-1,469	-1,590
Net cash used in investing activities	-12,594	-85,443
Financing Activities
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	247,244	78,246
Net increase (decrease) in time deposits	-5,862	30,662
Net increase (decrease) in short-term borrowings	-17,231	33,803
Cash dividends paid	-7,899	-6,881
Proceeds from directors’ stock plans and exercise of stock options, net of shares withheld	447	867
Cash paid for payroll taxes upon conversion of share-based awards	-658	-477
Net cash provided by financing activities	216,041	136,220
Net increase in cash and cash equivalents	210,918	71,597
Cash and cash equivalents at beginning of period	183,020	310,788
Cash and cash equivalents at end of period	393,938	382,385
Supplemental Disclosure of Cash Flow Information:
Interest paid	3,426	3,858
Loans transferred to other real estate and repossessed assets	3,662	2,098
Income Taxes Paid	$9,800	$0

Significant_Accounting_Policie

Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies
	Nature of Operations
	Chemical Financial Corporation (Corporation) operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operated through one commercial bank, Chemical Bank, as of March 31, 2015. Monarch Community Bank was acquired in the April 1, 2015 acquisition of Monarch Community Bancorp, Inc. (Monarch). The Corporation intends to consolidate Monarch Community Bank with and into Chemical Bank during the second quarter of 2015. Chemical Bank operates within the State of Michigan as a state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of four regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’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 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 and wealth management revenue.
	Basis of Presentation
	The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the interim consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2014. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the three months ended March 31, 2015 are not necessarily indicative of the results that may be expected for the year ending December 31, 2015.
	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, fair value amounts related to business combinations, pension expense, income taxes, goodwill impairment and those assets that require fair value measurement. Actual results could differ from these estimates.
	Business Combinations
	Pursuant to the guidance of 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.
	ASC 805 affords a measurement period beyond the acquisition date that allows the Corporation the opportunity to finalize the acquisition accounting in the event that new information is identified that existed as of the acquisition date but was not known by the Corporation at that time. The Corporation anticipates that measurement period adjustments may arise from adjustments to the fair values of assets and liabilities recognized at the acquisition date for Northwestern Bancorp, Inc. (Northwestern) as additional information is obtained, such as appraisals of collateral securing loans and other borrower information. In the event that a measurement period adjustment is identified, the Corporation will recognize the adjustment as part of its acquisition accounting, which may result in an adjustment to goodwill being recorded.
	See Note 2 for further information regarding the Corporation's completed and pending acquisition transactions.
	Originated Loans
	Originated loans include all of the Corporation's portfolio loans, excluding loans acquired on October 31, 2014 in the acquisition of Northwestern and on April 30, 2010 in the acquisition of O.A.K. Financial Corporation (OAK). Originated loans also include loans acquired as part of the Corporation's branch acquisition on December 7, 2012, as these loans were performing and were considered high-quality loans in accordance with the Corporation's credit underwriting standards at that date. 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.
	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 more (except for a loan that is secured by residential real estate, which is transferred to nonaccrual status at 120 days past due), 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, 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 October 31, 2014 in the acquisition of Northwestern and on April 30, 2010 in the acquisition of 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, through a fair value discount that was, in part, attributable to deterioration in credit quality. 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 fair value discount was recorded as a reduction of the acquired loans’ outstanding principal balances in the consolidated statement of financial position at the acquisition date.
	The Corporation accounts for acquired loans, which are recorded at fair value at acquisition, in accordance with Accounting Standards Codification (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 4 pools in the acquisition of Northwestern and 14 pools in the acquisition of OAK 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. If an individual loan is removed from a pool of loans, the difference between its relative carrying amount and the cash, fair value of the collateral, or other assets received would not affect the effective yield used to recognize the accretable difference on the remaining pool. 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. 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 (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 or interest rate, which generally would not otherwise be considered. The Corporation’s TDRs include performing and nonperforming TDRs, which consist of originated loans that continue to accrue interest at the loan's original interest rate 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. At the time of modification (except for loans on nonaccrual status), a TDR is reported as a nonperforming TDR until a six-month payment history of principal and interest payments, in accordance with the terms of the loan modification, is sustained, at which time the Corporation moves the loan to a performing status (performing TDR). If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR. 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 refinancing is no longer reported as a TDR.
	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. 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 classified as a nonperforming TDR until a six-month payment history is sustained, at which time the loan is classified as a performing TDR. Since no loss is expected to be incurred on these loans, no additional provision for loan losses has been recognized related to these loans, and these loans accrue interest at their contractual interest rate. These loans are individually evaluated for impairment and 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.
	Loans in the Corporation’s consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a performing or nonperforming TDR generally consist of residential mortgage loans that 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. These loans are moved to nonaccrual status if they become 90 days past due as to principal or interest payments, or sooner if conditions warrant.
	Impaired Loans
	A loan is defined to be impaired when it is probable that payment of principal and interest will not be paid in accordance with the original contractual terms of the loan agreement. Impaired loans include nonaccrual loans (including nonaccrual TDRs), performing and nonperforming TDRs and acquired loans that were not performing in accordance with original contractual terms. 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 an allocation of the 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), accruing originated loans contractually past due 90 days or more as to interest or principal payments and nonperforming 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.
	Allowance for Loan Losses
	The allowance for loan losses (allowance) is presented as a reserve against loans. The allowance represents management’s assessment of probable loan losses inherent in the Corporation’s loan portfolio.
	Management’s evaluation of the adequacy of the allowance is based on a continuing review of the loan portfolio, actual loan loss experience, the underlying value of the collateral, risk characteristics of the loan portfolio, the level and composition of nonperforming loans, the financial condition of the borrowers, the balance of the loan portfolio, loan growth, economic conditions, employment levels in the Corporation’s local markets, and special factors affecting specific business sectors. The Corporation maintains formal policies and procedures to monitor and control credit risk. Management evaluates the allowance on a quarterly basis in an effort to ensure the level is appropriate to absorb probable losses inherent in the loan portfolio.
	The allowance provides for probable losses that have been identified with specific customer relationships and for probable losses believed to be incurred in the remainder of the originated loan portfolio, but that have not been specifically identified. The Corporation utilizes its own loss experience to estimate inherent losses on loans. Internal risk ratings are assigned to each loan in the commercial loan portfolio (commercial, commercial real estate, real estate construction and land development loans) at the time of origination and are subject to subsequent periodic reviews by senior management. The Corporation performs a detailed credit quality review quarterly on all loans greater than $0.25 million that have deteriorated below certain levels of credit risk, and may allocate a specific portion of the allowance to such loans based upon this review. A portion of the allowance is allocated to the remaining loans by applying projected loss ratios, based on numerous factors. Projected loss ratios incorporate factors such as charge-off experience, trends with respect to adversely risk-rated loans in the commercial loan portfolio, trends with respect to past due and nonaccrual loans, changes in economic conditions and trends, changes in the value of underlying collateral and other credit risk factors. This evaluation involves a high degree of uncertainty.
	In determining the allowance and the related provision for loan losses, the Corporation considers four principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans in the commercial loan portfolio, (ii) reserves established for adversely-rated loans in the commercial loan portfolio and nonaccrual residential mortgage, consumer installment and home equity loans based on loan loss experience of other adversely-rated loans, (iii) reserves, by loan classes, on all other loans based principally on a five-year historical loan loss experience, with higher weighting placed on the most recent years, loan loss trends giving consideration to estimated loss emergence periods and (iv) an unallocated allowance based on the imprecision in the overall allowance methodology for loans collectively evaluated for impairment.
	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 process, 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.
	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. The fair value option (i) may be applied instrument by instrument, with certain exceptions, allowing the Corporation to record identical financial assets and liabilities at fair value or by another measurement basis permitted under GAAP, (ii) is irrevocable (unless a new election date occurs) and (iii) is applied only to entire instruments and not to portions of instruments. At March 31, 2015, December 31, 2014 and March 31, 2014, the Corporation had elected the fair value option on all of its residential mortgage loans held-for-sale. The Corporation has not elected the fair value option for any other financial assets or liabilities.
	Share-Based Compensation
	The Corporation grants stock options, stock awards, restricted stock performance units and restricted stock service-based units 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 of the award. The fair values of both stock options and stock awards are recognized as compensation expense on a straight-line basis over the requisite service period. The Corporation accounts for restricted stock performance units 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 restricted stock performance units 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 restricted stock service-based units 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 restricted stock service-based units. The fair value of the restricted stock service-based units is recognized as compensation expense over the requisite service period.
	Cash flows realized from the tax benefits of exercised stock option awards that result from actual tax deductions that are in excess of the recorded tax benefits related to the compensation expense recognized for those options (excess tax benefits) are classified as financing activities on the consolidated statements of cash flows.
	Income and Other Taxes
	The Corporation is subject to the income and other tax laws of the United States, the State of Michigan 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.
	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% 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 March 31, 2015, December 31, 2014 or March 31, 2014. The tax periods open to examination by the Internal Revenue Service include the calendar years ended December 31, 2014, 2013, 2012 and 2011.
	Investments in Qualified Affordable Housing Projects
	The Corporation invests in qualified affordable housing projects solely for the purpose of obtaining tax credits and other tax benefits. Accordingly, the Corporation believes that amortizing its investments in qualified affordable housing projects as a component of income tax expense rather than as a component of operating expenses better reflects the nature and intent of these investments. The Corporation recognized additional income tax expense attributable to the amortization of investments in qualified affordable housing projects of $0.1 million during each of the three months ended March 31, 2015 and 2014. The Corporation's remaining investment in qualified affordable housing projects totaled $4.8 million at March 31, 2015, $4.9 million at December 31, 2014 and $3.2 million at March 31, 2014.
	Shareholders’ 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 March 31, 2015, there were 500,000 remaining shares available for repurchase under the Corporation’s stock repurchase program.
	Underwritten Public Offerings of Common Stock
	On June 24, 2014, the Corporation issued and sold 2,500,000 shares of common stock at a public offering price of $28.00 per share. An additional 375,000 shares were issued and sold on June 30, 2014 upon the exercise in full of the underwriters' over-allotment option. The net proceeds from the issuance and sale of the common stock of this $80.5 million offering, after deducting the underwriting discount and issuance-related expenses, totaled $76.2 million.
	On September 18, 2013, the Corporation issued and sold 2,213,750 shares of common stock, including 288,750 shares of common stock that were issued and sold upon the exercise in full of the underwriters' over-allotment option, at a public offering price of $26.00 per share. The net proceeds from the issuance and sale of the common stock, after deducting the underwriting discount and issuance-related expenses, totaled $53.9 million.
	Shelf Registration
	On June 12, 2014, the Corporation filed an automatic shelf registration statement on Form S-3 with the Securities and Exchange Commission (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, 2009, the shareholders of the Corporation authorized the board of directors of the Corporation to issue up to 200,000 shares of preferred stock in connection with either an acquisition by the Corporation of an entity that has shares of preferred stock issued and outstanding pursuant to any program established by the United States government or participation by the Corporation in any program established by the United States government. On April 20, 2015, the shareholders of the Corporation approved an amendment to the restated articles of incorporation which eliminates and replaces the previous class of 200,000 shares of preferred stock with a new class of 2,000,000 shares of preferred stock. At March 31, 2015, no shares of preferred stock were issued and outstanding.
	Common Stock
	On April 20, 2015, 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 45,000,000 to 60,000,000.
	Legal Matters
	The Corporation and Chemical Bank are subject to certain legal actions arising in the ordinary course of business. In the opinion of management, after consultation with legal counsel, the ultimate disposition of these matters is not expected to have a material adverse effect on the consolidated financial condition or results of operations of the Corporation.
	Adopted Accounting Pronouncements
In-Substance Foreclosures
In January 2014, the FASB issued ASU 2014-04, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40): Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-04). ASU 2014-04 clarifies that an in-substance foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (i) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (ii) the borrower conveying all interest in the residential real estate property to the creditor to satisfy the loan through completion of a deed in lieu of foreclosure or similar legal agreement. ASU 2014-04 also requires disclosure of both the amount of foreclosed residential real estate property held by the creditor and the recorded investment in loans collateralized by residential real estate property that are in the process of foreclosure. ASU 2014-04 is effective for public companies for interim and annual periods beginning after December 15, 2014, with early adoption permitted. Once adopted, an entity can elect either (i) a modified retrospective transition method or (ii) a prospective transition method. The modified retrospective transition method is applied by means of a cumulative-effect adjustment to residential mortgage loans and foreclosed residential real estate properties existing as of the beginning of the period for which the amendments of ASU 2014-04 are effective, with real estate reclassified to loans measured at the carrying value of the real estate at the date of adoption and loans reclassified to real estate measured at the lower of net carrying value of the loan or the fair value of the real estate less costs to sell at the date of adoption. The prospective transition method is applied by means of applying the amendments of ASU 2014-04 to all instances of receiving physical possession of residential real estate properties that occur after the date of adoption. The adoption of ASU 2014-04 on January 1, 2015 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
Share-Based Compensation
In June 2014, the FASB issued ASU 2014-12, Compensation—Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period, a consensus of the FASB Emerging Issues Task Force (ASU 2014-12). ASU 2014-12 requires that a performance target that affects vesting of share-based payment awards and that could be achieved after the requisite service period be treated as a performance condition. Compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which the requisite service has already been rendered. If the performance target becomes probable of being achieved before the end of the requisite service period, the remaining unrecognized compensation cost should be recognized prospectively over the remaining requisite service period. The total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest and should be adjusted to reflect those awards that ultimately vest. The requisite service period ends when the employee can cease rendering service and still be eligible to vest in the award if the performance target is achieved. ASU 2014-12 is effective for all entities for interim and annual periods beginning after December 15, 2015, with early adoption permitted. An entity may apply the amendments in ASU 2014-12 either (i) prospectively to all awards granted or modified after the effective date or (ii) retrospectively to all awards with performance targets that are outstanding as of the beginning of the earliest annual period presented in the financial statements and to all new or modified awards thereafter. The Corporation's early adoption of ASU 2014-12 on January 1, 2015 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
Government-Guaranteed Mortgage Loans
In August 2014, the FASB issued ASU 2014-14, Receivables-Troubled Debt Restructurings by Creditors (Subtopic 310-40): Classification of Certain Government Guaranteed Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-14). ASU 2014-14 provides clarifying guidance related to how creditors classify government-guaranteed loans upon foreclosure. Upon foreclosure of a government-guaranteed mortgage loan, the loan should be derecognized and a separate other receivable should be recognized if the following conditions are met: (i) the loan has a government guarantee that is not separable from the loan before foreclosure; (ii) at the time of foreclosure, the creditor has the intent to convey the real estate property to the guarantor and make a claim on the guarantee, and the creditor has the ability to recover under that claim; and (iii) at the time of foreclosure, any amount of the claim that is determined on the basis of the fair value of the real estate is fixed. The separate other receivable should be measured based on the amount of the loan balance (principal and interest) expected to be recovered from the guarantor at the time of foreclosure. ASU 2014-14 is effective for public companies for interim and annual periods beginning after December 15, 2014. An entity should adopt using either the modified retrospective method or the prospective transition method. An entity must apply the same method elected under ASU 2014-04. Early adoption is permitted if the entity has already adopted ASU 2014-04. The adoption of ASU 2014-14 on January 1, 2015 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
Pending Accounting Pronouncements
There are no recent accounting pronouncements that have been issued by the FASB that would have a material impact on the financial statements of the Corporation.

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Acquisitions	Acquisitions
	Pending Acquisition of Lake Michigan Financial Corporation
	On January 5, 2015, the Corporation entered into an Agreement and Plan of Merger with Lake Michigan Financial Corporation (Lake Michigan). Under the terms of the merger agreement, each Lake Michigan shareholder will receive $16.64 in cash and 1.326 shares of the Corporation's common stock for each share of Lake Michigan common stock. Based on the 30-day volume weighted price per share of the Corporation's common stock as of January 5, 2015, the merger has a transaction value of approximately $184.1 million. The merger has received regulatory approval. Completion of the merger is subject to the approval of Lake Michigan's shareholders, in addition to satisfaction of other customary closing conditions.
	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 approximately 861,000 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. There are no contingencies resulting from the acquisition.
	Monarch, a bank holding company, owned Monarch Community Bank, which operates five full service branch offices in Coldwater, Marshall, Hillsdale and Union City, Michigan. Monarch Community Bank will be operated as a separate subsidiary of the Corporation until its planned consolidation with and into Chemical Bank in May 2015. At March 31, 2015, and without the effect of fair value purchase accounting adjustments, Monarch had total assets of $170 million, total loans of $128 million and total deposits of $143 million.
	Certain disclosures are required by the Corporation for business combinations that have occurred after the reporting date but before the financial statements are issued, unless the initial accounting for the business combination is incomplete at the time the financial statements are issued. The Corporation is in the process of completing its initial accounting related to the acquisition of Monarch, including finalizing the fair values of the assets acquired and liabilities assumed, and expects to have this information available for disclosure when it files its Quarterly Report on Form 10-Q for the quarter ending June 30, 2015.
	Acquisition of Northwestern Bancorp, Inc.
	On October 31, 2014, the Corporation acquired all of the outstanding stock of Northwestern Bancorp, Inc. (Northwestern) for total cash consideration of $121 million. Northwestern, a bank holding company which owned Northwestern Bank, provided traditional banking services and products through 25 banking offices serving communities in the northwestern lower peninsula of Michigan. At the acquisition date, Northwestern added total assets of $815 million, including total loans of $475 million, and total deposits of $794 million to the Corporation. Northwestern Bank was consolidated with and into Chemical Bank as of the acquisition date. In connection with the acquisition of Northwestern, the Corporation recorded $60.0 million of goodwill, which was primarily attributable to the synergies and economies of scale expected from combining the operations of the Corporation and Northwestern. In addition, the Corporation recorded $12.9 million of core deposit intangible assets in conjunction with the acquisition.
	Upon acquisition, the Northwestern loan portfolio had contractually required principal and interest payments receivable of $507 million and $112 million, respectively, expected principal and interest cash flows of $481 million and $104 million, respectively, and a fair value of $475 million. The difference between the contractually required payments receivable and the expected cash flows represents the nonaccretable difference, which totaled $34 million at the acquisition date, with $26 million attributable to expected credit losses. The difference between the expected cash flows and fair value represents the accretable yield, which totaled $110 million at the acquisition date. The outstanding contractual principal balance and the carrying amount of the Northwestern acquired loan portfolio were $453 million and $421 million, respectively, at March 31, 2015, compared to $485 million and $452 million, respectively, at December 31, 2014.
	Acquisition of 21 Branches
	On December 7, 2012, Chemical Bank acquired 21 branches from Independent Bank, a subsidiary of Independent Bank Corporation, located in the Northeast and Battle Creek regions of Michigan, including $404 million in deposits and $44 million in loans (branch acquisition transaction). The purchase price of the branch offices, including equipment, was $8.1 million and the Corporation paid a premium on deposits of $11.5 million, or approximately 2.85% of total deposits. The loans were purchased at a discount of 1.75%. In connection with the branch acquisition transaction, the Corporation recorded goodwill of $6.8 million and other intangible assets attributable to customer core deposits of $5.6 million.
	Acquisition of O.A.K. Financial Corporation (OAK)
	On April 30, 2010, the Corporation acquired OAK in an all-stock transaction for total consideration of $83.7 million. OAK provided traditional banking services and products through 14 banking offices serving communities in Ottawa, Allegan and Kent counties in west Michigan. At the acquisition date, OAK added total assets of $820 million, including total loans of $627 million, and total deposits of $693 million, including brokered deposits of $193 million. Upon acquisition, the OAK loan portfolio had contractually required principal payments receivable of $683 million and a fair value of $627 million. The outstanding contractual principal balance and the carrying amount of the OAK acquired loan portfolio were $255 million and $234 million, respectively, at March 31, 2015, compared to $268 million and $246 million, respectively, at December 31, 2014 and $313 million and $289 million, respectively, at March 31, 2014.
	Accretable Yield
	Activity for the accretable yield, which includes contractually due interest for acquired loans that have been renewed or extended since the date of acquisition and continue to be accounted for in loan pools in accordance with ASC 310-30, follows:
			Three Months Ended March 31,
			2015									2014
			Northwestern			OAK			Total			OAK
			(In thousands)
	Balance at beginning of period		$	104,675		$	33,286		137,961			$	32,610
	Additions (reductions)*		(1,410		)	714			(696		)	821
	Accretion recognized in interest income		(4,998		)	(3,207		)	(8,205		)	(3,843		)
	Reclassification from nonaccretable difference		—			—			—			10,000
	Balance at end of period		$	98,267		$	30,793		$	129,060		$	39,588
	*	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.

Investment_Securities

Investment Securities	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015, December 31, 2014 and March 31, 2014:
		Investment Securities Available-for-Sale
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	31-Mar-15
	U.S. Treasury securities	$	8,271	$	31	$	—	$	8,302
	Government sponsored agencies	249,642		889		101		250,430
	State and political subdivisions	31,701		624		3		32,322
	Residential mortgage-backed securities	218,299		1,358		56		219,601
	Collateralized mortgage obligations	133,713		305		718		133,300
	Corporate bonds	34,925		136		64		34,997
	Preferred stock	1,389		303		—		1,692
	Total	$	677,940	$	3,646	$	942	$	680,644
	31-Dec-14
	U.S. Treasury securities	$	8,272	$	—	$	13	$	8,259
	Government sponsored agencies	263,658		356		511		263,503
	State and political subdivisions	45,157		1,087		17		46,227
	Residential mortgage-backed securities	240,465		885		1,543		239,807
	Collateralized mortgage obligations	145,316		261		1,194		144,383
	Corporate bonds	44,930		213		48		45,095
	Preferred stock	1,389		201		—		1,590
	Total	$	749,187	$	3,003	$	3,326	$	748,864
	31-Mar-14
	Government sponsored agencies	$	91,613	$	295	$	298	$	91,610
	State and political subdivisions	42,369		1,408		—		43,777
	Residential mortgage-backed securities	291,187		1,023		3,472		288,738
	Collateralized mortgage obligations	167,622		393		1,296		166,719
	Corporate bonds	65,003		505		93		65,415
	Preferred stock	1,389		170		—		1,559
	Total	$	659,183	$	3,794	$	5,159	$	657,818
		Investment Securities Held-to-Maturity
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	31-Mar-15
	State and political subdivisions	$	370,950	$	6,852	$	4,926	$	372,876
	Trust preferred securities	10,500		—		3,200		7,300
	Total	$	381,450	$	6,852	$	8,126	$	380,176
	31-Dec-14
	State and political subdivisions	$	305,913	$	7,294	$	4,557	$	308,650
	Trust preferred securities	10,500		—		3,410		7,090
	Total	$	316,413	$	7,294	$	7,967	$	315,740
	31-Mar-14
	State and political subdivisions	$	267,599	$	5,331	$	6,983	$	265,947
	Trust preferred securities	10,500		—		4,040		6,460
	Total	$	278,099	$	5,331	$	11,023	$	272,407
	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).
	At March 31, 2015, the Corporation held $10.5 million of trust preferred investment securities that were recorded as held-to-maturity, with $10.0 million of these securities representing a 100% interest in a trust preferred investment security of a small non-public bank holding company in Michigan that has been assessed by the Corporation as financially strong. The remaining $0.5 million represents a 10% interest in another trust preferred investment security of a small non-public bank holding company located in Michigan that was categorized as well-capitalized under regulatory guidelines at March 31, 2015.
	At March 31, 2015, it was the Corporation’s opinion that the market for trust preferred investment securities was not active, and thus, in accordance with GAAP, when there is a significant decrease in the volume and activity for an asset or liability in relation to normal market activity, adjustments to transaction or quoted prices may be necessary or a change in valuation technique or multiple valuation techniques may be appropriate. The Corporation obtained pricing information for its trust preferred investment securities from an independent third-party pricing source. The pricing information was based on both observable inputs and unobservable inputs, including appropriate risk adjustments that market participants would make for possible nonperformance, illiquidity and issuer specifics such as size, leverage position and location. The observable inputs were based on the existing market and insight into appropriate rate of return adjustments that market participants would require for the additional risk associated with a single issue investment security of this nature. Based on the information obtained from the independent third-party pricing source, the Corporation calculated a fair value at March 31, 2015 of $7.0 million on its $10.0 million trust preferred investment security and $0.3 million on its $0.5 million trust preferred investment security, resulting in a combined unrealized loss of $3.2 million at that date.
	The following is a summary of the amortized cost and fair value of investment securities at March 31, 2015, 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.
		31-Mar-15
		Amortized		Fair Value
		Cost
		(In thousands)
	Investment Securities Available-for-Sale:
	Due in one year or less	$	180,558	$	180,869
	Due after one year through five years	442,088		443,752
	Due after five years through ten years	50,902		51,302
	Due after ten years	3,003		3,029
	Preferred stock	1,389		1,692
	Total	$	677,940	$	680,644
	Investment Securities Held-to-Maturity:
Due in one year or less	$	35,293	$	35,365
Due after one year through five years	171,557		172,699
Due after five years through ten years	120,799		122,512
Due after ten years	53,801		49,600
Total	$	381,450	$	380,176
The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at March 31, 2015, December 31, 2014 and March 31, 2014, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position.
	Less Than 12 Months				12 Months or More				Total
	Fair		Gross		Fair		Gross		Fair		Gross
	Value		Unrealized		Value		Unrealized		Value		Unrealized
			Losses				Losses				Losses
	(In thousands)
31-Mar-15
U.S. Treasury securities	$	—	$	—	$	—	$	—	$	—	$	—
Government sponsored agencies	27,889		64		18,896		37		46,785		101
State and political subdivisions	156,010		1,989		49,839		2,940		205,849		4,929
Residential mortgage-backed securities	82,303		28		3,847		28		86,150		56
Collateralized mortgage obligations	22,694		22		41,061		696		63,755		718
Corporate bonds	4,989		11		14,946		53		19,935		64
Trust preferred securities	—		—		7,300		3,200		7,300		3,200
Total	$	293,885	$	2,114	$	135,889	$	6,954	$	429,774	$	9,068
31-Dec-14
U.S. Treasury securities	$	8,259	$	13	$	—	$	—	$	8,259	$	13
Government sponsored agencies	166,963		406		31,927		105		198,890		511
State and political subdivisions	62,310		3,348		36,847		1,226		99,157		4,574
Residential mortgage-backed securities	17,276		52		180,194		1,491		197,470		1,543
Collateralized mortgage obligations	63,077		179		31,620		1,015		94,697		1,194
Corporate bonds	—		—		14,952		48		14,952		48
Trust preferred securities	—		—		7,090		3,410		7,090		3,410
Total	$	317,885	$	3,998	$	302,630	$	7,295	$	620,515	$	11,293
31-Mar-14
Government sponsored agencies	$	45,396	$	110	$	15,204	$	188	$	60,600	$	298
State and political subdivisions	79,787		4,942		56,180		2,041		135,967		6,983
Residential mortgage-backed securities	247,397		3,472		—		—		247,397		3,472
Collateralized mortgage obligations	76,900		885		12,833		411		89,733		1,296
Corporate bonds	—		—		14,907		93		14,907		93
Trust preferred securities	—		—		6,460		4,040		6,460		4,040
Total	$	449,480	$	9,409	$	105,584	$	6,773	$	555,064	$	16,182
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 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, as of March 31, 2015, represented an other-than-temporary impairment (OTTI). Management believed that the unrealized losses on investment securities at March 31, 2015 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. Unrealized losses of $3.2 million in the trust preferred securities portfolio, related to trust preferred securities of two well-capitalized bank holding companies in Michigan, were attributable to illiquidity in financial markets for these types of investments. The Corporation performed an analysis of the creditworthiness of these issuers and concluded that, at March 31, 2015, the Corporation expected to recover the entire amortized cost basis of these investment securities.
At March 31, 2015, 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 March 31, 2015, 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	3 Months Ended
	Mar. 31, 2015
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 seven 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 — 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 — 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 March 31, 2015, December 31, 2014 and March 31, 2014 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. 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 loans follows:
			March 31,				December 31,				March 31,
			2015				2014				2014
			(In thousands)
	Commercial loan portfolio:
	Commercial		$	1,356,169			$	1,354,881			$	1,208,641
	Commercial real estate		1,616,923				1,557,648				1,279,167
	Real estate construction		95,923				152,745				85,084
	Land development		12,916				18,750				13,761
	Subtotal		3,081,931				3,084,024				2,586,653
	Consumer loan portfolio:
	Residential mortgage		1,117,445				1,110,390				962,009
	Consumer installment		844,066				829,570				675,412
	Home equity		659,432				664,246				529,215
	Subtotal		2,620,943				2,604,206				2,166,636
	Total loans		$	5,702,874			$	5,688,230			$	4,753,289
	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 across the lower peninsula of Michigan, except for the southeastern portion of Michigan. The Corporation has no foreign loans.
	The Corporation 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 $1.0 million requiring group loan authority approval, except for six executive and senior officers who have varying limits exceeding $1.5 million and up to $3.5 million. During the first quarter of 2015, the Corporation increased the upper range for each level of group loan authority by$5.0 million, resulting in group loan authorities as follows. The Corporation has a loan committee, consisting of certain executive and senior officers, that meets weekly to consider loans ranging in amounts from $1.0 million to $10.0 million, depending on risk rating and credit action required. A directors’ loan committee, consisting of eight independent members of the board of directors, the chief executive officer and senior credit officer, meets bi-weekly to consider loans in amounts over $10.0 million, and certain loans under $10.0 million depending on a loan’s risk rating and credit action required. Loans over $15.0 million require majority 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
	The Corporation uses a nine grade risk rating system to monitor the ongoing credit quality of its commercial loan portfolio. These loan grades rank the credit quality of a borrower by measuring liquidity, debt capacity, coverage and payment behavior as shown in the borrower’s financial statements. The loan grades also measure the quality of the borrower’s management and the repayment support offered by any guarantors. A summary of the Corporation’s loan grades (or characteristics of the loans within each grade) follows:
	Risk Grades 1-5 (Acceptable Credit Quality) — All loans in risk grades 1 through 5 are considered to be acceptable credit risks by the Corporation and are grouped for purposes of allowance for loan loss considerations and financial reporting. The five grades essentially represent a ranking of loans that are all viewed to be of acceptable credit quality, taking into consideration the various factors mentioned above, but with varying degrees of financial strength, debt coverage, management and factors that could impact credit quality. Business credits within risk grades 1 through 5 range from Risk Grade 1: Prime Quality (factors include: excellent business credit; excellent debt capacity and coverage; outstanding management; strong guarantors; superior liquidity and net worth; favorable loan-to-value ratios; debt secured by cash or equivalents, or backed by the full faith and credit of the U.S. Government) to Risk Grade 5: Acceptable Quality With Care (factors include: acceptable business credit, but with added risk due to specific industry or internal situations).
	Risk Grade 6 (Watch) — A business credit that is not acceptable within the Corporation’s loan origination criteria; cash flow may not be adequate or is continually inconsistent to service current debt; financial condition has deteriorated as company trends/management have become inconsistent; the company is slow in furnishing quality financial information; working capital needs of the company are reliant on short-term borrowings; personal guarantees are weak and/or with little or no liquidity; the net worth of the company has deteriorated after recent or continued losses; the loan requires constant monitoring and attention from the Corporation; payment delinquencies becoming more serious; if left uncorrected, these potential weaknesses may, at some future date, result in deterioration of repayment prospects.
	Risk Grade 7 (Substandard — Accrual) — A business credit that is inadequately protected by the current financial net worth and paying capacity of the obligor or of the collateral pledged, if any; management has deteriorated or has become non-existent; quality financial information is not available; a high level of maintenance is required by the Corporation; cash flow can no longer support debt requirements; loan payments are continually and/or severely delinquent; negative net worth; personal guaranty has become insignificant; a credit that has a well-defined weakness or weaknesses that jeopardize the liquidation of the debt. The Corporation still expects a full recovery of all contractual principal and interest payments; however, a possibility exists that the Corporation will sustain some loss if deficiencies are not corrected.
	Risk Grade 8 (Substandard — Nonaccrual) — A business credit accounted for on a nonaccrual basis that has all the weaknesses inherent in a loan classified as risk grade 7 with the added characteristic that the weaknesses are so pronounced that, on the basis of current financial information, conditions, and values, collection in full is highly questionable; a partial loss is possible and interest is no longer being accrued. This loan meets the definition of an impaired loan. The risk of loss requires analysis to determine whether a valuation allowance needs to be established.
	Risk Grade 9 (Substandard — Doubtful) — A business credit that has all the weaknesses inherent in a loan classified as risk grade 8 and interest is no longer being accrued, but additional deficiencies make it highly probable that liquidation will not satisfy the majority of the obligation; the primary source of repayment is nonexistent and there is doubt as to the value of the secondary source of repayment; the possibility of loss is likely, but current pending factors could strengthen the credit. This loan meets the definition of an impaired loan. A loan charge-off is recorded when management deems an amount uncollectible; however, the Corporation will establish a valuation allowance for probable losses, if required.
	The Corporation considers all loans graded 1 through 5 as acceptable credit risks and structures and manages such relationships accordingly. Periodic financial and operating data combined with regular loan officer interactions are deemed adequate to monitor borrower performance. Loans graded 6 and 7 are considered higher-risk credits than loans graded 1 through 5 and the frequency of loan officer contact and receipt of financial data is increased to stay abreast of borrower performance. Loans graded 8 and 9 are considered problematic and require special care. Further, loans graded 6 through 9 are managed and monitored regularly through a number of processes, procedures and committees, including oversight by a loan administration committee comprised of executive and senior management of the Corporation, which include highly structured reporting of financial and operating data, intensive loan officer intervention and strategies to exit, as well as potential management by the Corporation’s special assets group.
	The following schedule presents the recorded investment of loans in the commercial loan portfolio by risk rating categories at March 31, 2015, December 31, 2014 and March 31, 2014:
			Commercial				Commercial Real Estate				Real Estate			Land			Total
											Construction			Development
			(In thousands)
	31-Mar-15
	Originated Portfolio:
	Risk Grades 1-5		$	1,176,021			$	1,175,373			$	93,864		$	2,633		$	2,447,891
	Risk Grade 6		40,999				44,248				—			738			85,985
	Risk Grade 7		28,983				27,961				1,396			601			58,941
	Risk Grade 8		18,904				24,760				663			290			44,617
	Risk Grade 9		—				6				—			—			6
	Subtotal		1,264,907				1,272,348				95,923			4,262			2,637,440
	Acquired Portfolio:
	Risk Grades 1-5		71,422				318,113				—			6,724			396,259
	Risk Grade 6		11,299				7,786				—			253			19,338
	Risk Grade 7		6,509				12,735				—			140			19,384
	Risk Grade 8		2,032				5,941				—			1,537			9,510
	Risk Grade 9		—				—				—			—			—
	Subtotal		91,262				344,575				—			8,654			444,491
	Total		$	1,356,169			$	1,616,923			$	95,923		$	12,916		$	3,081,931
	31-Dec-14
	Originated Portfolio:
	Risk Grades 1-5		$	1,171,817			$	1,114,529			$	134,668		$	2,952		$	2,423,966
	Risk Grade 6		37,800				34,996				1,408			738			74,942
Risk Grade 7		29,863				29,935				2,502			613			62,913
Risk Grade 8		16,417				24,958				162			225			41,762
Risk Grade 9		1				8				—			—			9
Subtotal		1,255,898				1,204,426				138,740			4,528			2,603,592
Acquired Portfolio:
Risk Grades 1-5		76,780				321,018				14,005			11,789			423,592
Risk Grade 6		12,687				8,698				—			583			21,968
Risk Grade 7		4,089				12,478				—			197			16,764
Risk Grade 8		5,427				11,028				—			1,653			18,108
Risk Grade 9		—				—				—			—			—
Subtotal		98,983				353,222				14,005			14,222			480,432
Total		$	1,354,881			$	1,557,648			$	152,745		$	18,750		$	3,084,024
31-Mar-14
Originated Portfolio:
Risk Grades 1-5		$	1,060,743			$	1,034,517			$	70,750		$	3,831		$	2,169,841
Risk Grade 6		18,359				33,962				680			968			53,969
Risk Grade 7		33,768				32,671				815			700			67,954
Risk Grade 8		17,301				27,552				160			2,267			47,280
Risk Grade 9		950				16				—			—			966
Subtotal		1,131,121				1,128,718				72,405			7,766			2,340,010
Acquired Portfolio:
Risk Grades 1-5		67,326				139,130				12,679			3,906			223,041
Risk Grade 6		2,423				2,627				—			—			5,050
Risk Grade 7		3,635				7,753				—			—			11,388
Risk Grade 8		4,136				939				—			2,089			7,164
Risk Grade 9		—				—				—			—			—
Subtotal		77,520				150,449				12,679			5,995			246,643
Total		$	1,208,641			$	1,279,167			$	85,084		$	13,761		$	2,586,653
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 or classified as a nonperforming TDR are considered to be in a nonperforming status. Nonaccrual TDRs in the consumer loan portfolio are included with nonaccrual loans, while other TDRs in the consumer loan portfolio are considered in a nonperforming status until they meet the Corporation’s definition of a performing TDR, at which time they are considered in a performing 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 March 31, 2015, December 31, 2014 and March 31, 2014:
		Residential Mortgage				Consumer				Home Equity			Total
						Installment							Consumer
		(In thousands)
31-Mar-15
Originated Loans:
Performing		$	998,196			$	834,926			$	565,992		$	2,399,114
Nonperforming		9,376				433				2,299			12,108
Subtotal		1,007,572				835,359				568,291			2,411,222
Acquired Loans:
Performing		109,005				8,696				90,686			208,387
Nonperforming		868				11				455			1,334
Subtotal		109,873				8,707				91,141			209,721
Total		$	1,117,445			$	844,066			$	659,432		$	2,620,943
31-Dec-14
Originated Loans:
Performing		$	987,542			$	818,878			$	566,083		$	2,372,503
Nonperforming		10,459				500				3,013			13,972
Subtotal		998,001				819,378				569,096			2,386,475
Acquired Loans:
Performing		111,101				10,174				94,696			215,971
Nonperforming		1,288				18				454			1,760
Subtotal		112,389				10,192				95,150			217,731
Total		$	1,110,390			$	829,570			$	664,246		$	2,604,206
31-Mar-14
Originated Loans:
Performing		$	937,968			$	672,984			$	497,196		$	2,108,148
Nonperforming		12,833				806				2,668			16,307
Subtotal		950,801				673,790				499,864			2,124,455
Acquired Loans:
Performing		11,150				1,622				29,020			41,792
Nonperforming		58				—				331			389
Subtotal		11,208				1,622				29,351			42,181
Total		$	962,009			$	675,412			$	529,215		$	2,166,636
Nonperforming Loans
A summary of nonperforming loans follows:
		March 31,				December 31,				March 31,
		2015				2014				2014
		(In thousands)
Nonaccrual loans:
Commercial		$	18,904			$	16,418			$	18,251
Commercial real estate		24,766				24,966				27,568
Real estate construction		663				162				160
Land development		290				225				2,267
Residential mortgage		6,514				6,706				6,589
Consumer installment		433				500				806
Home equity		1,870				1,667				2,046
Total nonaccrual loans		53,440				50,644				57,687
Accruing loans contractually past due 90 days or more as to interest or principal payments:
Commercial		52				170				43
Commercial real estate		148				—				730
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		172				557				—
Consumer installment		—				—				—
Home equity		429				1,346				622
Total accruing loans contractually past due 90 days or more as to interest or principal payments		801				2,073				1,395
Nonperforming TDRs:
Commercial loan portfolio		15,810				15,271				11,218
Consumer loan portfolio		2,690				3,196				6,244
Total nonperforming TDRs		18,500				18,467				17,462
Total nonperforming loans		$	72,741			$	71,184			$	76,544
The Corporation’s nonaccrual loans at March 31, 2015, December 31, 2014 and March 31, 2014 included $37.3 million, $37.2 million and $44.4 million, respectively, of nonaccrual TDRs.
The Corporation had $2.2 million of residential mortgage loans that were in the process of foreclosure at March 31, 2015.
Impaired Loans
The following schedule presents impaired loans by classes of loans at March 31, 2015, December 31, 2014 and March 31, 2014:
		Recorded				Unpaid				Related
		Investment				Principal				Valuation
						Balance				Allowance
		(In thousands)
31-Mar-15
Impaired loans with a valuation allowance:
Commercial		$	3,433			$	3,527			$	1,119
Commercial real estate		1,780				1,961				496
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		19,887				19,887				297
Subtotal		25,100				25,375				1,912
Impaired loans with no related valuation allowance:
Commercial		33,733				39,382				—
Commercial real estate		57,628				79,696				—
Real estate construction		663				836				—
Land development		1,877				3,428				—
Residential mortgage		7,382				7,382				—
Consumer installment		444				444				—
Home equity		2,325				2,325				—
Subtotal		104,052				133,493				—
Total impaired loans:
Commercial		37,166				42,909				1,119
Commercial real estate		59,408				81,657				496
Real estate construction		663				836				—
Land development		1,877				3,428				—
Residential mortgage		27,269				27,269				297
Consumer installment		444				444				—
Home equity		2,325				2,325				—
Total		$	129,152			$	158,868			$	1,912
31-Dec-14
Impaired loans with a valuation allowance:
Commercial		$	966			$	1,040			$	293
Commercial real estate		2,587				2,927				710
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		19,681				19,681				335
Subtotal		23,234				23,648				1,338
Impaired loans with no related valuation allowance:
Commercial		38,094				44,557				—
Commercial real estate		60,616				82,693				—
Real estate construction		162				255				—
Land development		1,928				3,484				—
Residential mortgage		7,994				7,994				—
Consumer installment		518				518				—
Home equity		2,121				2,121				—
Subtotal		111,433				141,622				—
Total impaired loans:
Commercial		39,060				45,597				293
Commercial real estate		63,203				85,620				710
Real estate construction		162				255				—
Land development		1,928				3,484				—
Residential mortgage		27,675				27,675				335
Consumer installment		518				518				—
Home equity		2,121				2,121				—
Total		$	134,667			$	165,270			$	1,338
		Recorded				Unpaid				Related
		Investment				Principal				Valuation
						Balance				Allowance
		(In thousands)
31-Mar-14
Impaired loans with a valuation allowance:
Commercial		$	3,534			$	3,704			$	1,250
Commercial real estate		3,720				3,878				371
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		19,944				19,944				444
Subtotal		27,198				27,526				2,065
Impaired loans with no related valuation allowance:
Commercial		38,150				42,914				—
Commercial real estate		49,074				62,207				—
Real estate construction		160				366				—
Land development		4,472				7,773				—
Residential mortgage		6,589				6,589				—
Consumer installment		806				806				—
Home equity		2,046				2,046				—
Subtotal		101,297				122,701				—
Total impaired loans:
Commercial		41,684				46,618				1,250
Commercial real estate		52,794				66,085				371
Real estate construction		160				366				—
Land development		4,472				7,773				—
Residential mortgage		26,533				26,533				444
Consumer installment		806				806				—
Home equity		2,046				2,046				—
Total		$	128,495			$	150,227			$	2,065
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, and for acquired loans that meet the definition of an impaired loan represents fair value adjustments recognized at the acquisition date attributable to expected credit losses and the discounting of expected cash flows at market interest rates. The difference between the recorded investment and the unpaid principal balance of $29.7 million, $30.6 million and $21.7 million at March 31, 2015, December 31, 2014 and March 31, 2014, respectively, includes confirmed losses (partial charge-offs) of $14.8 million, $15.4 million and $17.8 million, respectively, and fair value discount adjustments of $14.9 million, $15.2 million and $3.9 million, respectively.
Impaired loans included $11.2 million, $19.9 million and $11.5 million at March 31, 2015, December 31, 2014 and March 31, 2014, respectively, of acquired loans that were not performing in accordance with original contractual terms. Acquired loans that are not performing in accordance with contractual terms are not reported as nonperforming loans 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. Impaired loans also included $46.0 million, $45.7 million and $41.8 million at March 31, 2015, December 31, 2014 and March 31, 2014, respectively, of performing TDRs.
The following schedule presents information related to impaired loans for the three months ended March 31, 2015 and 2014:
		Three Months Ended March 31, 2015
		Average				Interest Income
		Recorded				Recognized
		Investment				While on
						Impaired Status
		(In thousands)
Commercial		$	38,576			$	289
Commercial real estate		60,240				525
Real estate construction		640				—
Land development		1,875				27
Residential mortgage		27,352				331
Consumer installment		499				—
Home equity		2,352				8
Total		$	131,534			$	1,180
		Three Months Ended March 31, 2014
		Average				Interest Income
		Recorded				Recognized
		Investment				While on
						Impaired Status
		(In thousands)
Commercial		$	41,607			$	333
Commercial real estate		53,320				361
Real estate construction		167				—
Land development		4,643				37
Residential mortgage		26,781				303
Consumer installment		773				—
Home equity		2,168				—
Total		$	129,459			$	1,034
The following schedule presents the aging status of the recorded investment in loans by classes of loans at March 31, 2015, December 31, 2014 and March 31, 2014:
		31-60				61-89				Accruing			Non-accrual			Total		Current		Total
		Days				Days				Loans			Loans			Past Due				Loans
		Past Due				Past Due				Past Due
										90 Days
										or More
		(In thousands)
31-Mar-15
Originated Portfolio:
Commercial		$	10,121			$	729			$	52		$	18,904		$	29,806	$	1,235,101	$	1,264,907
Commercial real estate		7,238				2,267				148			24,766			34,419		1,237,929		1,272,348
Real estate construction		340				—				—			663			1,003		94,920		95,923
Land development		—				—				—			290			290		3,972		4,262
Residential mortgage		1,246				88				172			6,514			8,020		999,552		1,007,572
Consumer installment		2,143				344				—			433			2,920		832,439		835,359
Home equity		1,728				197				429			1,870			4,224		564,067		568,291
Total		$	22,816			$	3,625			$	801		$	53,440		$	80,682	$	4,967,980	$	5,048,662
Acquired Portfolio:
Commercial		$	59			$	5			$	2,089		$	—		$	2,153	$	89,109	$	91,262
Commercial real estate		1,784				138				6,271			—			8,193		336,382		344,575
Real estate construction		—				—				—			—			—		—		—
Land development		—				—				1,537			—			1,537		7,117		8,654
Residential mortgage		104				—				868			—			972		108,901		109,873
Consumer installment		3				1				11			—			15		8,692		8,707
Home equity		349				234				455			—			1,038		90,103		91,141
Total		$	2,299			$	378			$	11,231		$	—		$	13,908	$	640,304	$	654,212
		31-60				61-89				Accruing			Non-accrual			Total		Current		Total
		Days				Days				Loans			Loans			Past Due				Loans
		Past Due				Past Due				Past Due
										90 Days
										or More
		(In thousands)
31-Dec-14
Originated Portfolio:
Commercial		$	4,033			$	743			$	170		$	16,418		$	21,364	$	1,234,534	$	1,255,898
Commercial real estate		7,515				1,383				—			24,966			33,864		1,170,562		1,204,426
Real estate construction		262				—				—			162			424		138,316		138,740
Land development		—				—				—			225			225		4,303		4,528
Residential mortgage		2,126				54				557			6,706			9,443		988,558		998,001
Consumer installment		3,620				512				—			500			4,632		814,746		819,378
Home equity		3,039				660				1,346			1,667			6,712		562,384		569,096
Total		$	20,595			$	3,352			$	2,073		$	50,644		$	76,664	$	4,913,403	$	4,990,067
Acquired Portfolio:
Commercial		$	133			$	—			$	5,427		$	—		$	5,560	$	93,423	$	98,983
Commercial real estate		2,014				352				11,052			—			13,418		339,804		353,222
Real estate construction		—				—				—			—			—		14,005		14,005
Land development		—				—				1,653			—			1,653		12,569		14,222
Residential mortgage		156				—				18			—			174		112,215		112,389
Consumer installment		55				3				454			—			512		9,680		10,192
Home equity		636				106				1,288			—			2,030		93,120		95,150
Total		$	2,994			$	461			$	19,892		$	—		$	23,347	$	674,816	$	698,163
31-Mar-14
Originated Portfolio:
Commercial		$	6,003			$	1,832			$	43		$	18,251		$	26,129	$	1,104,992	$	1,131,121
Commercial real estate		4,094				1,098				730			27,568			33,490		1,095,228		1,128,718
Real estate construction		18				—				—			160			178		72,227		72,405
Land development		—				—				—			2,267			2,267		5,499		7,766
Residential mortgage		1,259				1,138				—			6,589			8,986		941,815		950,801
Consumer installment		1,950				313				—			806			3,069		670,721		673,790
Home equity		1,500				256				622			2,046			4,424		495,440		499,864
Total		$	14,824			$	4,637			$	1,395		$	57,687		$	78,543	$	4,385,922	$	4,464,465
Acquired Portfolio:
Commercial		$	—			$	—			$	6,496		$	—		$	6,496	$	71,024	$	77,520
Commercial real estate		—				—				2,549			—			2,549		147,900		150,449
Real estate construction		—				—				—			—			—		12,679		12,679
Land development		—				—				2,089			—			2,089		3,906		5,995
Residential mortgage		—				—				58			—			58		11,150		11,208
Consumer installment		49				—				—			—			49		1,573		1,622
Home equity		49				—				331			—			380		28,971		29,351
Total		$	98			$	—			$	11,523		$	—		$	11,621	$	277,203	$	288,824
Loans Modified Under Troubled Debt Restructurings (TDRs)
The following schedule presents the Corporation’s loans reported as TDRs at March 31, 2015, December 31, 2014 and March 31, 2014:
		Performing TDRs				Non-Performing TDRs				Nonaccrual TDRs			Total
		(In thousands)
31-Mar-15
Commercial loan portfolio		$	28,784			$	15,810			$	32,917		$	77,511
Consumer loan portfolio		17,197				2,690				4,426			24,313
Total		$	45,981			$	18,500			$	37,343		$	101,824
31-Dec-14
Commercial loan portfolio		$	29,179			$	15,271			$	32,597		$	77,047
Consumer loan portfolio		16,485				3,196				4,594			24,275
Total		$	45,664			$	18,467			$	37,191		$	101,322
31-Mar-14
Commercial loan portfolio		$	28,123			$	11,218			$	40,511		$	79,852
Consumer loan portfolio		13,700				6,244				3,875			23,819
Total		$	41,823			$	17,462			$	44,386		$	103,671
The following schedule provides information on the Corporation's TDRs that were modified during the three months ended March 31, 2015 and 2014:
	Number			Pre-				Post-
	of Loans			Modification				Modification
				Recorded				Recorded
				Investment				Investment
	(Dollars in thousands)
Three Months Ended March 31, 2015
Commercial loan portfolio:
Commercial	5			$	1,932			$	1,932
Commercial real estate	5			2,534				2,534
Land development	—			—				—
Subtotal – commercial loan portfolio	10			4,466				4,466
Consumer loan portfolio	10			336				336
Total	20			$	4,802			$	4,802
Three Months Ended March 31, 2014
Commercial loan portfolio:
Commercial	12			$	8,356			$	8,356
Commercial real estate	9			2,790				2,790
Real estate construction	—			—				—
Land development	1			72				72
Subtotal – commercial loan portfolio	22			11,218				11,218
Consumer loan portfolio	30			987				978
Total	52			$	12,205			$	12,196
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 includes TDRs for which there was a payment default during the three months ended March 31, 2015 and 2014, 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:
		Number of			Principal Balance at End of Period
		Loans
		(Dollars in thousands)
Three Months Ended March 31, 2015
Commercial loan portfolio:
Commercial		—			$	—
Commercial real estate		3			759
Subtotal – commercial loan portfolio		3			759
Consumer loan portfolio		1			33
Total		4			$	792
Three Months Ended March 31, 2014
Commercial loan portfolio:
Commercial		1			$	104
Commercial real estate		2			1,670
Real estate construction		—			—
Land development		—			—
Subtotal – commercial loan portfolio		3			1,774
Consumer loan portfolio		—			—
Total		3			$	1,774
Allowance for Loan Losses
The following schedule presents, by loan portfolio segment, the changes in the allowance for the three months ended March 31, 2015 and details regarding the balance in the allowance and the recorded investment in loans at March 31, 2015 by impairment evaluation method.
		Commercial				Consumer				Unallocated			Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
Changes in allowance for loan losses for the three months ended March 31, 2015:
Beginning balance		$	44,156			$	28,803			$	2,724		$	75,683
Provision for loan losses		3,593				(3,227		)		1,134			1,500
Charge-offs		(1,504		)		(1,639		)		—			(3,143		)
Recoveries		574				642				—			1,216
Ending balance		$	46,819			$	24,579			$	3,858		$	75,256
Allowance for loan losses balance at March 31, 2015 attributable to:
Loans individually evaluated for impairment		$	1,615			$	297			$	—		$	1,912
Loans collectively evaluated for impairment		45,204				24,282				3,858			73,344
Loans acquired with deteriorated credit quality		—				—				—			—
Total		$	46,819			$	24,579			$	3,858		$	75,256
Recorded investment (loan balance) at March 31, 2015:
Loans individually evaluated for impairment		$	89,217			$	19,887			$	—		$	109,104
Loans collectively evaluated for impairment		2,548,223				2,391,335				—			4,939,558
Loans acquired with deteriorated credit quality		444,491				209,721				—			654,212
Total		$	3,081,931			$	2,620,943			$	—		$	5,702,874
The following schedule presents, by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2014 by impairment evaluation method.
		Commercial				Consumer				Unallocated			Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
Allowance for loan losses balance at December 31, 2014 attributable to:
Loans individually evaluated for impairment		$	1,003			$	335			$	—		$	1,338
Loans collectively evaluated for impairment		43,153				27,968				2,724			73,845
Loans acquired with deteriorated credit quality		—				500				—			500
Total		$	44,156			$	28,803			$	2,724		$	75,683
Recorded investment (loan balance) at December 31, 2014:
Loans individually evaluated for impairment		$	86,221			$	19,681			$	—		$	105,902
Loans collectively evaluated for impairment		2,517,371				2,366,794				—			4,884,165
Loans acquired with deteriorated credit quality		480,432				217,731				—			698,163
Total		$	3,084,024			$	2,604,206			$	—		$	5,688,230
The following schedule presents, by loan portfolio segment, the changes in the allowance for the three months ended March 31, 2014 and details regarding the balance in the allowance and the recorded investment in loans at March 31, 2014 by impairment evaluation method.
		Commercial				Consumer				Unallocated			Total
		Loan				Loan
		Portfolio				Portfolio
		(In thousands)
Changes in allowance for loan losses for the three months ended March 31, 2014:
Beginning balance		$	44,482			$	30,145			$	4,445		$	79,072
Provision for loan losses		960				855				(215		)	1,600
Charge-offs		(1,209		)		(2,263		)		—			(3,472		)
Recoveries		777				496				—			1,273
Ending balance		$	45,010			$	29,233			$	4,230		$	78,473
Allowance for loan losses balance at March 31, 2014 attributable to:
Loans individually evaluated for impairment		$	1,621			$	444			$	—		$	2,065
Loans collectively evaluated for impairment		43,389				28,289				4,230			75,908
Loans acquired with deteriorated credit quality		—				500				—			500
Total		$	45,010			$	29,233			$	4,230		$	78,473
Recorded investment (loan balance) at March 31, 2014:
Loans individually evaluated for impairment		$	87,587			$	19,944			$	—		$	107,531
Loans collectively evaluated for impairment		2,252,423				2,104,511				—			4,356,934
Loans acquired with deteriorated credit quality		246,643				42,181				—			288,824
Total		$	2,586,653			$	2,166,636			$	—		$	4,753,289
The allowance attributable to acquired loans of $0.5 million at December 31, 2014 and March 31, 2014 was primarily attributable to two consumer loan pools in the acquired loan portfolio that had a decline in expected cash flows. There were no material changes in expected cash flows for the remaining acquired loan pools at March 31, 2015, December 31, 2014 or March 31, 2014.

Intangible_Assets

Intangible Assets	3 Months Ended
	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible Assets
	The Corporation has the following types of intangible assets: goodwill, core deposit intangible assets and mortgage servicing rights (MSRs). Goodwill and core deposit intangible assets arose as a result of business combinations or other acquisitions. MSRs arose as a result of selling residential mortgage loans in the secondary market while retaining the right to service these loans and receive servicing income over the life of the loan. Amortization is recorded on the core deposit intangible assets and MSRs. Goodwill is not amortized but is evaluated at least annually for impairment. The Corporation’s most recent annual goodwill impairment test performed as of October 31, 2014 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 March 31, 2015 and that the Corporation's goodwill was not impaired at March 31, 2015.
	The following table shows the net carrying value of the Corporation’s intangible assets:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Goodwill	$	180,128		$	180,128		$	120,164
	Other intangible assets:
	Core deposit intangible assets	$	20,072		$	20,863		$	9,556
	Mortgage servicing rights	11,583			12,217			3,316
	Total other intangible assets	$	31,655		$	33,080		$	12,872
	The following table sets forth the carrying amount, accumulated amortization and amortization expense of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Gross original amount	$	30,122		$	31,550		$	18,659
	Accumulated amortization	10,050			10,687			9,103
	Carrying amount	$	20,072		$	20,863		$	9,556
	Amortization expense for the three months ended March 31	$	791					$	445
	The estimated future amortization expense on core deposit intangible assets for periods ending after March 31, 2015 is as follows: 2015 — $2.4 million; 2016 — $2.9 million; 2017 — $2.6 million; 2018 — $2.5 million; 2019 — $2.4 million; 2020 and thereafter — $7.2 million.
	The following shows the net carrying value and fair value of MSRs and the total loans that the Corporation is servicing for others:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Net carrying value of MSRs	$	11,583		$	12,217		$	3,316
	Fair value of MSRs	$	14,378		$	14,979		$	6,706
	Loans serviced for others that have servicing rights capitalized	$	2,062,544		$	2,093,140		$	877,530
	The following table shows the activity for capitalized MSRs:
		Three Months Ended March 31,
		2015			2014
		(In thousands)
	Balance at beginning of period	$	12,217		$	3,423
	Additions	400			143
	Amortization	(1,034		)	(250		)
	Balance at end of period	$	11,583		$	3,316
	MSRs are stratified into servicing assets originated by the Corporation and those acquired in acquisitions of other institutions and further stratified into relatively homogeneous pools based on products with similar characteristics. There was a valuation allowance of $0.2 million as of March 31, 2015 and December 31, 2014 related to impairment within certain pools attributable to the Corporation's servicing portfolio that was acquired in the Northwestern transaction. There was no impairment valuation allowance recorded on the Corporation's MSRs at March 31, 2014.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss, net of related tax benefit/expense, were as follows:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Net unrealized gains (losses) on investment securities – available-for-sale, net of related tax expense (benefit) of $946 at March 31, 2015, $(113) at December 31, 2014 and $(478) at March 31, 2014	$	1,758		$	(210	)	$	(887	)
	Pension and other postretirement benefits adjustment, net of related tax benefit of $16,981 at March 31, 2015, $17,362 at December 31, 2014 and $9,915 at March 31, 2014	(31,537		)	(32,243		)	(18,414		)
	Accumulated other comprehensive loss	$	(29,779	)	$	(32,453	)	$	(19,301	)

Regulatory_Capital

Regulatory Capital	3 Months Ended
	Mar. 31, 2015
Banking and Thrift [Abstract]
Regulatory Capital	Regulatory Capital
	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 March 31, 2015, substantially all of the assets of Chemical Bank were restricted from transfer to the Corporation in the form of loans or advances. Dividends from Chemical Bank are the principal source of funds for the Corporation. At March 31, 2015, Chemical Bank was "well-capitalized" as defined by federal banking regulations. In addition to the statutory limits, the Corporation considers the overall financial and capital position of Chemical Bank prior to making any cash dividend decisions.
	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 Corporation’s consolidated financial statements.
	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 of the Corporation totaled $5.58 billion, $5.70 billion and $4.76 billion at March 31, 2015, December 31, 2014 and March 31, 2014, respectively.
	In July 2013, the Federal Reserve Board and FDIC approved final rules implementing the Basel Committee on Banking Supervision's (BCBS) capital guidelines for U.S. banks. The final rules, which are subject to a multi-year phase-in period, began for the Corporation and Chemical Bank on January 1, 2015. The final rules include a new minimum common equity Tier 1 capital to risk-weighted assets (CET) ratio of 4.5%, in addition to raising the minimum ratio of Tier 1 capital to risk-weighted assets from 4.0% to 6.0% and requiring a minimum leverage ratio of 4.0%. The final rules also establish 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.
	At March 31, 2015, December 31, 2014 and March 31, 2014, 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.
	The summary below compares the Corporation’s and Chemical Bank’s actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy:
		Actual				Minimum Required for Capital Adequacy Purposes				Required to be Well Capitalized Under Prompt Corrective Action Regulations
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
		(Dollars in thousands)
	31-Mar-15
	Total Capital to Risk-Weighted Assets:
	Corporation	$	727,090	13	%	$	446,173	8	%	N/A		N/A
	Chemical Bank	676,488		12.1		445,471		8		$	556,838	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	657,307		11.8		334,630		6		N/A		N/A
	Chemical Bank	606,813		10.9		334,103		6		445,471		8
	Common Equity Tier 1 Capital to Risk-Weighted Assets:
	Corporation	657,307		11.8		250,972		4.5		N/A		N/A
	Chemical Bank	606,813		10.9		250,577		4.5		361,945		6.5
	Leverage Ratio:
	Corporation	657,307		9.1		289,948		4		N/A		N/A
	Chemical Bank	606,813		8.4		289,840		4		362,300		5
	31-Dec-14
	Total Capital to Risk-Weighted Assets:
	Corporation	$	705,130	12.4	%	$	456,302	8	%	N/A		N/A
	Chemical Bank	654,031		11.5		455,633		8		$	569,541	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	633,779		11.1		228,151		4		N/A		N/A
	Chemical Bank	582,783		10.2		227,816		4		341,725		6
	Leverage Ratio:
	Corporation	633,779		9.3		273,226		4		N/A		N/A
	Chemical Bank	582,783		8.5		273,048		4		341,310		5
	31-Mar-14
	Total Capital to Risk-Weighted Assets:
	Corporation	$	659,644	13.8	%	$	381,146	8	%	N/A		N/A
	Chemical Bank	589,254		12.4		380,542		8		$	475,678	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	599,856		12.6		190,573		4		N/A		N/A
	Chemical Bank	529,560		11.1		190,271		4		285,407		6
	Leverage Ratio:
	Corporation	599,856		9.9		243,070		4		N/A		N/A
	Chemical Bank	529,560		8.7		242,939		4		303,673		5

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
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 to determine fair value disclosures. Investment securities — available-for-sale and loans held-for-sale 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 would 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 and preferred stock. Valuations are obtained from a third-party pricing service for these investment securities.
	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, trust preferred investment securities, impaired loans, goodwill, core deposit intangible assets, MSRs 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. 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 — 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.
	The Corporation elected the fair value option for all residential mortgage loans held-for-sale originated on or after July 1, 2012. 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.
	Disclosure of Recurring Basis Fair Value Measurements
	For assets measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets were as follows:
			Fair Value Measurements – Recurring Basis
			Quoted Prices			Significant			Significant			Total
			In Active			Other			Unobservable
			Markets for			Observable			Inputs
			Identical			Inputs			(Level 3)
			Assets			(Level 2)
			(Level 1)
			(In thousands)
	31-Mar-15
	Investment securities – available-for-sale:
	U.S. Treasury securities		$	8,302		$	—		$	—		$	8,302
	Government sponsored agencies		—			250,430			—			250,430
	State and political subdivisions		—			32,322			—			32,322
	Residential mortgage-backed securities		—			219,601			—			219,601
	Collateralized mortgage obligations		—			133,300			—			133,300
	Corporate bonds		—			34,997			—			34,997
	Preferred stock		—			1,692			—			1,692
	Total investment securities – available-for-sale		8,302			672,342			—			680,644
	Loans held-for-sale		—			9,675			—			9,675
	Total assets measured at fair value on a recurring basis		$	8,302		$	682,017		$	—		$	690,319
	31-Dec-14
	Investment securities – available-for-sale:
	U.S. Treasury securities		$	8,259		$	—		$	—		$	8,259
	Government sponsored agencies		—			263,503			—			263,503
	State and political subdivisions		—			46,227			—			46,227
	Residential mortgage-backed securities		—			239,807			—			239,807
	Collateralized mortgage obligations		—			144,383			—			144,383
	Corporate bonds		—			45,095			—			45,095
	Preferred stock		—			1,590			—			1,590
	Total investment securities – available-for-sale		8,259			740,605			—			748,864
	Loans held-for-sale		—			9,128			—			9,128
	Total assets measured at fair value on a recurring basis		$	8,259		$	749,733		$	—		$	757,992
	31-Mar-14
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	91,610		$	—		$	91,610
	State and political subdivisions		—			43,777			—			43,777
	Residential mortgage-backed securities		—			288,738			—			288,738
	Collateralized mortgage obligations		—			166,719			—			166,719
	Corporate bonds		—			65,415			—			65,415
	Preferred stock		—			1,559			—			1,559
	Total investment securities – available-for-sale		—			657,818			—			657,818
	Loans held-for-sale		—			3,814			—			3,814
	Total assets measured at fair value on a recurring basis		$	—		$	661,632		$	—		$	661,632
	There were no liabilities recorded at fair value on a recurring basis at March 31, 2015, December 31, 2014 or March 31, 2014.
	Assets and Liabilities Recorded at Fair Value on a Nonrecurring Basis
	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 independent appraised value, or management determines the fair value of the collateral is further impaired below the appraised value. When management determines the fair value of the collateral is further impaired below appraised value, discount factors ranging between 70% and 80% of the appraised value are used depending on the nature of the collateral and the age of the most recent appraisal.
	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 March 31, 2015, December 31, 2014 and March 31, 2014, no goodwill was impaired, and therefore, goodwill was not recorded at fair value on a nonrecurring basis.
	Other intangible assets consist of core deposit intangible assets and MSRs. These items are both recorded at fair value when initially recorded. Subsequently, core deposit intangible assets are amortized primarily on an accelerated basis over periods ranging from ten to fifteen years 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 impairment is identified, the Corporation classifies impaired core deposit intangible assets subject to nonrecurring fair value measurements as Level 3 valuations. At March 31, 2015, December 31, 2014 and March 31, 2014, there was no impairment identified for core deposit intangible assets. The fair value of MSRs is 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, MSRs are adjusted to fair value, as determined by the model, through a valuation allowance. The Corporation classifies MSRs subject to nonrecurring fair value measurements as Level 3 valuations. At March 31, 2015 and December 31, 2014, the Corporation recognized a valuation allowance of $0.2 million related to impairment within certain pools attributable to the Corporation's servicing portfolio that was acquired in the Northwestern transaction. At March 31, 2014, there was no impairment identified for MSRs and, therefore, no other intangible assets were recorded at fair value on a nonrecurring basis at that date.
	The carrying amounts for other real estate (ORE) and repossessed assets (RA) are reported in the consolidated statements of financial position under “Interest receivable and other assets.” ORE and RA include real estate and other types of assets repossessed by the Corporation. ORE and RA are recorded at the lower of cost or fair value upon the transfer of a loan to ORE or RA and, subsequently, ORE and RA 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 ORE and RA 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, discount factors ranging between 70% and 75% 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 were as follows:
		Fair Value Measurements – Nonrecurring Basis
		Quoted Prices			Significant			Significant			Total
		In Active			Other			Unobservable
		Markets for			Observable			Inputs
		Identical			Inputs			(Level 3)
		Assets			(Level 2)
		(Level 1)
		(In thousands)
31-Mar-15
Impaired originated loans		$	—		$	—		$	23,730		$	23,730
Other real estate/repossessed assets		—			—			14,744			14,744
Mortgage servicing rights		—			—			8,115			8,115
Total		$	—		$	—		$	46,589		$	46,589
31-Dec-14
Impaired originated loans		$	—		$	—		$	21,323		$	21,323
Other real estate/repossessed assets		—			—			14,205			14,205
Mortgage servicing rights		—			—			8,691			8,691
Total		$	—		$	—		$	44,219		$	44,219
31-Mar-14
Impaired originated loans		$	—		$	—		$	29,461		$	29,461
Other real estate/repossessed assets		—			—			10,056			10,056
Total		$	—		$	—		$	39,517		$	39,517
There were no liabilities recorded at fair value on a nonrecurring basis at March 31, 2015, December 31, 2014 and March 31, 2014.
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 ASC 820, Fair Value Measurements and Disclosures, 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 March 31, 2015, December 31, 2014 and March 31, 2014, 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.
Fair value measurement for investment securities — held-to-maturity is based upon quoted prices, if available. If quoted prices are not available, 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 the majority of the Corporation's investment securities issued by state and political subdivisions. Level 3 valuations include certain securities issued by state and political subdivisions and trust preferred investment securities.
Fair value measurements of nonmarketable equity securities, which consisted 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 held-for-sale are carried at fair value, as the Corporation elected the fair value option on these loans. 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.
The fair value of variable interest rate loans that reprice regularly with changes in market interest rates are based on carrying values. The fair values for fixed interest rate loans are estimated using discounted cash flow analyses, using the Corporation’s interest rates currently being offered for loans with similar terms to borrowers of similar credit quality. The resulting fair value amounts are adjusted to estimate the impact of changes in the credit quality of borrowers after the loans were originated. The fair value measurements for loans are Level 3 valuations.
The fair values of deposit accounts without defined maturities, such as interest- and noninterest-bearing checking, savings and money market accounts, are equal to the amounts payable on demand. 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 Level 3 valuations. The fair values for variable-interest rate time deposits with defined maturities approximate their carrying amounts.
Short-term borrowings consist of securities sold under agreements to repurchase, short-term FHLB advances and federal funds purchased. 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.
Fair value measurements for long-term FHLB advances are estimated 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.
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.
Fair value measurements have not been made for items that are not defined by GAAP as financial instruments, including such items as the value of the Corporation’s Wealth Management department and the value of the Corporation’s core deposit base. The Corporation believes it is impractical to estimate a representative fair value for these types of assets, even though management believes they add significant value to the Corporation.
A summary of carrying amounts and estimated fair values of the Corporation’s financial instruments included in the consolidated statements of financial position was as follows:
	Level in Fair Value Measurement		31-Mar-15						31-Dec-14					31-Mar-14
	Hierarchy		Carrying			Fair			Carrying			Fair		Carrying		Fair
			Amount			Value			Amount			Value		Amount		Value
			(In thousands)
Assets:
Cash and cash equivalents	Level 1		$	393,938		$	393,938		$	183,020		$	183,020	$	382,385	$	382,385
Investment securities:
Available-for-sale	Level 1		8,302			8,302			8,259			8,259		—		—
Available-for-sale	Level 2		672,342			672,342			740,605			740,605		657,818		657,818
Held-to-maturity	Level 2		370,950			372,876			305,913			308,650		267,599		265,947
Held-to-maturity	Level 3		10,500			7,300			10,500			7,090		10,500		6,460
Nonmarketable equity securities	NA		31,249			31,249			27,369			27,369		25,572		25,572
Loans held-for-sale	Level 2		9,675			9,675			9,128			9,128		3,814		3,814
Net loans	Level 3		5,627,618			5,633,217			5,612,547			5,623,454		4,674,816		4,688,814
Interest receivable	Level 2		19,816			19,816			17,492			17,492		16,945		16,945
Liabilities:
Deposits without defined maturities	Level 2		$	4,988,268		$	4,988,268		$	4,741,024		$	4,741,024	$	3,868,700	$	3,868,700
Time deposits	Level 3		1,332,085			1,335,605			1,337,947			1,340,015		1,362,593		1,371,312
Interest payable	Level 2		779			779			755			755		876		876
Short-term borrowings	Level 2		372,236			372,236			389,467			389,467		361,231		361,231

Earnings_Per_Common_Share

Earnings Per Common Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share
	Basic earnings per common share for the Corporation is computed by dividing net income by the weighted average number of common shares outstanding during the period. Basic earnings per common share excludes any dilutive effect of common stock equivalents.
	Diluted earnings per common share for the Corporation is computed by dividing net income by the sum of the weighted average number of common shares outstanding and the dilutive effect of common stock equivalents using the treasury stock method. 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, stock to be issued under the deferred stock compensation plan for non-employee directors and stock to be issued under the stock purchase plan for non-employee advisory directors. For any period in which a net loss is recorded, the assumed exercise of stock options, restricted stock units that may be converted to stock and stock to be issued under the deferred stock compensation plan and the stock purchase plan would have an anti-dilutive impact on the net loss per common share and thus are excluded in the diluted earnings per common share calculation.
	The following summarizes the numerator and denominator of the basic and diluted earnings per common share computations:
		Three Months Ended March 31,
		2015		2014
		(In thousands, except per share data)
	Numerator for both basic and diluted earnings per common share, net income	$	17,835	$	13,813
	Denominator for basic earnings per common share, weighted average common shares outstanding	32,809		29,825
	Weighted average common stock equivalents	235		212
	Denominator for diluted earnings per common share	33,044		30,037
	Basic earnings per common share	$	0.54	$	0.46
	Diluted earnings per common share	0.54		0.46
	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 121,050 and 259,288 for the three months ended March 31, 2015 and 2014, respectively.

ShareBased_Compensation

Share-Based Compensation	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation
	The Corporation maintains a share-based compensation plan 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 three-month periods ended March 31, 2015 and 2014, share-based compensation expense related to stock options, restricted stock units and other share-based awards totaled $0.8 million and $0.6 million, respectively.
	During the three-month period ended March 31, 2015, the Corporation granted options to purchase 244,165 shares of common stock and 76,286 restricted stock units to certain officers. At March 31, 2015, there were 32,953 shares of common stock available for future grants under the share-based compensation plan. On April 20, 2015, the shareholders of the Corporation approved the Stock Incentive Plan of 2015, which provides for 1,300,000 shares of the Corporation's common stock to be made available for future equity-based awards and cancels the amount of shares available for future grant under prior share-based compensation plans.
	Stock Options
	The Corporation issues stock options to certain officers. Stock options are issued at the current market price of the Corporation's common stock on the date of grant and 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.
	A summary of activity for the Corporation’s stock options as of and for the three months ended March 31, 2015 is presented below:
			Non-Vested						Stock Options Outstanding
			Stock Options Outstanding
			Number of		Weighted-		Weighted-		Number of		Weighted-
			Options		Average		Average		Options		Average
					Exercise		Grant Date				Exercise
					Price		Fair Value Per Share				Price
					Per Share						Per Share
	Outstanding at December 31, 2014		432,199		$	26.75	$	8.3	1,037,311		$	25.9
	Granted		244,165		30.18		8.4		244,165		30.18
	Exercised		—		—		—		(37,191	)	23.11
	Vested		(150,224	)	25.57		7.8		—		—
	Forfeited/expired		(3,049	)	27.42		8.59		(3,049	)	27.42
	Outstanding at March 31, 2015		523,091		$	28.69	$	8.49	1,241,236		$	26.82
	Exercisable/vested at March 31, 2015								718,145		$	25.46
	The weighted-average remaining contractual terms were 6.6 years for all outstanding stock options and 4.7 years for exercisable stock options at March 31, 2015. The intrinsic value of all outstanding in-the-money stock options and exercisable in-the-money stock options was $5.7 million and $4.4 million, respectively, at March 31, 2015. The aggregate intrinsic values of outstanding and exercisable options at March 31, 2015 were calculated based on the closing market price of the Corporation’s common stock on March 31, 2015 of $31.36 per share less the exercise price. Options with intrinsic values less than zero, or “out-of-the-money” options, were not included in the aggregate intrinsic value reported.
	At March 31, 2015, unrecognized compensation expense related to stock options totaled $4.4 million and is expected to be recognized over a remaining weighted average period of 4.2 years.
	The fair value of the stock options granted during the three months ended March 31, 2015 was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions.
	Expected dividend yield	3.5		%
	Risk-free interest rate	1.78		%
	Expected stock price volatility	39.1		%
	Expected life of options – in years	7
	Weighted average fair value of options granted	$	8.4
	Restricted Stock Units
	In addition to stock options, the Corporation grants restricted stock performance units and restricted stock service-based units (collectively referred to as restricted stock units) to certain officers. The restricted stock performance units vest based on the Corporation achieving certain performance target levels. The restricted stock performance units are eligible to vest from 0.25x to 1.5x the number of units originally granted depending on which, if any, of the performance target levels are met. However, if the minimum performance target level is not achieved, no shares will become vested or be issued for that respective year’s restricted stock performance units. The restricted stock service-based units vest upon satisfaction of a service condition. Upon achievement of the performance target level and/or satisfaction of a service condition, if applicable, the restricted stock units are converted into shares of the Corporation’s common stock on a one-to-one basis. Compensation expense related to restricted stock units is recognized over the expected requisite performance or service period, as applicable.
	A summary of the activity for restricted stock units as of and for the three months ended March 31, 2015 is presented below:
			Number of		Weighted-
			Units		Average
					Grant Date
					Fair Value
					Per Unit
	Outstanding at December 31, 2014		204,319		$	24.14
	Granted		76,286		28.15
	Converted into shares of common stock		(66,769	)	22.32
	Forfeited/expired		(405	)	25.17
	Outstanding at March 31, 2015		213,431		$	26.14
	At March 31, 2015, unrecognized compensation expense related to restricted stock unit awards totaled $4.1 million and is expected to be recognized over a remaining weighted average period of 3.0 years.

Pension_and_Other_Postretireme

Pension and Other Postretirement Benefit Plans	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Benefit Plans	Pension and Other Postretirement Benefit Plans
	The components of net periodic benefit cost for the Corporation’s qualified and nonqualified pension plans and nonqualified postretirement benefit plan are as follows:
		Three Months Ended March 31,
		2015			2014
		(In thousands)
	Defined Benefit Pension Plans
	Service cost	$	273		$	250
	Interest cost	1,332			1,312
	Expected return on plan assets	(2,161		)	(2,078		)
	Amortization of prior service credit	(1		)	—
	Amortization of unrecognized net loss	1,056			569
	Net periodic benefit cost	$	499		$	53
	Postretirement Benefit Plan
	Service cost	$	4		$	5
	Interest cost	33			35
	Amortization of prior service cost	32			32
	Amortization of unrecognized net gain	—			(26		)
	Net periodic benefit cost	$	69		$	46
	The Corporation’s pension plan does not have a contribution requirement in 2015. The Corporation did not make a contribution to the pension plan during 2014. The discount rate used to compute the Corporation's pension plan expense for 2015 is 4.15%.
	401(k) Savings Plan expense for the Corporation’s match of participants’ base compensation contributions and a 4% of eligible pay contribution to certain employees who are not grandfathered under the pension plan was $1.1 million and $0.8 million for the three months ended March 31, 2015 and 2014, respectively.

Financial_Guarantees

Financial Guarantees	3 Months Ended
	Mar. 31, 2015
Guarantees [Abstract]
Financial Guarantees	Financial Guarantees
	In the normal course of business, the Corporation is a party to financial instruments containing credit risk that are not required to be reflected in the consolidated statements of financial position. For the Corporation, these financial instruments are financial and performance 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 March 31, 2015, December 31, 2014 and March 31, 2014, the Corporation had $38 million, $41 million and $45 million, respectively, of outstanding financial and performance standby letters of credit that expire in five years or less. 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 March 31, 2015, December 31, 2014 and March 31, 2014.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations
	Chemical Financial Corporation (Corporation) operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operated through one commercial bank, Chemical Bank, as of March 31, 2015. Monarch Community Bank was acquired in the April 1, 2015 acquisition of Monarch Community Bancorp, Inc. (Monarch). The Corporation intends to consolidate Monarch Community Bank with and into Chemical Bank during the second quarter of 2015. Chemical Bank operates within the State of Michigan as a state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of four regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’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 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 and wealth management revenue.
Basis of Presentation	Basis of Presentation
	The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the interim consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2014. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the three months ended March 31, 2015 are not necessarily indicative of the results that may be expected for the year ending December 31, 2015.
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, fair value amounts related to business combinations, pension expense, income taxes, goodwill impairment and those assets that require fair value measurement. Actual results could differ from these estimates.
Business Combinations Policy [Policy Text Block]	Business Combinations
	Pursuant to the guidance of 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.
	ASC 805 affords a measurement period beyond the acquisition date that allows the Corporation the opportunity to finalize the acquisition accounting in the event that new information is identified that existed as of the acquisition date but was not known by the Corporation at that time. The Corporation anticipates that measurement period adjustments may arise from adjustments to the fair values of assets and liabilities recognized at the acquisition date for Northwestern Bancorp, Inc. (Northwestern) as additional information is obtained, such as appraisals of collateral securing loans and other borrower information. In the event that a measurement period adjustment is identified, the Corporation will recognize the adjustment as part of its acquisition accounting, which may result in an adjustment to goodwill being recorded.
	See Note 2 for further information regarding the Corporation's completed and pending acquisition transactions.
Originated Loans	Originated Loans
	Originated loans include all of the Corporation's portfolio loans, excluding loans acquired on October 31, 2014 in the acquisition of Northwestern and on April 30, 2010 in the acquisition of O.A.K. Financial Corporation (OAK). Originated loans also include loans acquired as part of the Corporation's branch acquisition on December 7, 2012, as these loans were performing and were considered high-quality loans in accordance with the Corporation's credit underwriting standards at that date. 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.
	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 more (except for a loan that is secured by residential real estate, which is transferred to nonaccrual status at 120 days past due), 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, 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 October 31, 2014 in the acquisition of Northwestern and on April 30, 2010 in the acquisition of 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, through a fair value discount that was, in part, attributable to deterioration in credit quality. 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 fair value discount was recorded as a reduction of the acquired loans’ outstanding principal balances in the consolidated statement of financial position at the acquisition date.
	The Corporation accounts for acquired loans, which are recorded at fair value at acquisition, in accordance with Accounting Standards Codification (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 4 pools in the acquisition of Northwestern and 14 pools in the acquisition of OAK 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. If an individual loan is removed from a pool of loans, the difference between its relative carrying amount and the cash, fair value of the collateral, or other assets received would not affect the effective yield used to recognize the accretable difference on the remaining pool. 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. 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 troubled debt restructurings (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 or interest rate, which generally would not otherwise be considered. The Corporation’s TDRs include performing and nonperforming TDRs, which consist of originated loans that continue to accrue interest at the loan's original interest rate 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. At the time of modification (except for loans on nonaccrual status), a TDR is reported as a nonperforming TDR until a six-month payment history of principal and interest payments, in accordance with the terms of the loan modification, is sustained, at which time the Corporation moves the loan to a performing status (performing TDR). If the Corporation does not expect to collect all principal and interest on the loan, the modified loan is classified as a nonaccrual TDR. 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 refinancing is no longer reported as a TDR.
	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. 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 classified as a nonperforming TDR until a six-month payment history is sustained, at which time the loan is classified as a performing TDR. Since no loss is expected to be incurred on these loans, no additional provision for loan losses has been recognized related to these loans, and these loans accrue interest at their contractual interest rate. These loans are individually evaluated for impairment and 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.
	Loans in the Corporation’s consumer loan portfolio (comprised of residential mortgage, consumer installment and home equity loans) that meet the definition of a performing or nonperforming TDR generally consist of residential mortgage loans that 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. These loans are moved to nonaccrual status if they become 90 days past due as to principal or interest payments, or sooner if conditions warrant.
Impaired Loans	Impaired Loans
	A loan is defined to be impaired when it is probable that payment of principal and interest will not be paid in accordance with the original contractual terms of the loan agreement. Impaired loans include nonaccrual loans (including nonaccrual TDRs), performing and nonperforming TDRs and acquired loans that were not performing in accordance with original contractual terms. 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 an allocation of the 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), accruing originated loans contractually past due 90 days or more as to interest or principal payments and nonperforming 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.
Allowance for Loan Losses	Allowance for Loan Losses
	The allowance for loan losses (allowance) is presented as a reserve against loans. The allowance represents management’s assessment of probable loan losses inherent in the Corporation’s loan portfolio.
	Management’s evaluation of the adequacy of the allowance is based on a continuing review of the loan portfolio, actual loan loss experience, the underlying value of the collateral, risk characteristics of the loan portfolio, the level and composition of nonperforming loans, the financial condition of the borrowers, the balance of the loan portfolio, loan growth, economic conditions, employment levels in the Corporation’s local markets, and special factors affecting specific business sectors. The Corporation maintains formal policies and procedures to monitor and control credit risk. Management evaluates the allowance on a quarterly basis in an effort to ensure the level is appropriate to absorb probable losses inherent in the loan portfolio.
	The allowance provides for probable losses that have been identified with specific customer relationships and for probable losses believed to be incurred in the remainder of the originated loan portfolio, but that have not been specifically identified. The Corporation utilizes its own loss experience to estimate inherent losses on loans. Internal risk ratings are assigned to each loan in the commercial loan portfolio (commercial, commercial real estate, real estate construction and land development loans) at the time of origination and are subject to subsequent periodic reviews by senior management. The Corporation performs a detailed credit quality review quarterly on all loans greater than $0.25 million that have deteriorated below certain levels of credit risk, and may allocate a specific portion of the allowance to such loans based upon this review. A portion of the allowance is allocated to the remaining loans by applying projected loss ratios, based on numerous factors. Projected loss ratios incorporate factors such as charge-off experience, trends with respect to adversely risk-rated loans in the commercial loan portfolio, trends with respect to past due and nonaccrual loans, changes in economic conditions and trends, changes in the value of underlying collateral and other credit risk factors. This evaluation involves a high degree of uncertainty.
	In determining the allowance and the related provision for loan losses, the Corporation considers four principal elements: (i) valuation allowances based upon probable losses identified during the review of impaired loans in the commercial loan portfolio, (ii) reserves established for adversely-rated loans in the commercial loan portfolio and nonaccrual residential mortgage, consumer installment and home equity loans based on loan loss experience of other adversely-rated loans, (iii) reserves, by loan classes, on all other loans based principally on a five-year historical loan loss experience, with higher weighting placed on the most recent years, loan loss trends giving consideration to estimated loss emergence periods and (iv) an unallocated allowance based on the imprecision in the overall allowance methodology for loans collectively evaluated for impairment.
	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 process, 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.
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. The fair value option (i) may be applied instrument by instrument, with certain exceptions, allowing the Corporation to record identical financial assets and liabilities at fair value or by another measurement basis permitted under GAAP, (ii) is irrevocable (unless a new election date occurs) and (iii) is applied only to entire instruments and not to portions of instruments. At March 31, 2015, December 31, 2014 and March 31, 2014, the Corporation had elected the fair value option on all of its residential mortgage loans held-for-sale. The Corporation has not elected the fair value option for any other financial assets or liabilities.
Share-Based Compensation	Share-Based Compensation
	The Corporation grants stock options, stock awards, restricted stock performance units and restricted stock service-based units 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 of the award. The fair values of both stock options and stock awards are recognized as compensation expense on a straight-line basis over the requisite service period. The Corporation accounts for restricted stock performance units 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 restricted stock performance units 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 restricted stock service-based units 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 restricted stock service-based units. The fair value of the restricted stock service-based units is recognized as compensation expense over the requisite service period.
	Cash flows realized from the tax benefits of exercised stock option awards that result from actual tax deductions that are in excess of the recorded tax benefits related to the compensation expense recognized for those options (excess tax benefits) are classified as financing activities on the consolidated statements of cash flows.
Income and Other Taxes	Income and Other Taxes
	The Corporation is subject to the income and other tax laws of the United States, the State of Michigan 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.
	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% 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 March 31, 2015, December 31, 2014 or March 31, 2014. The tax periods open to examination by the Internal Revenue Service include the calendar years ended December 31, 2014, 2013, 2012 and 2011.
Investments in Qualified Affordable Housing Projects [Policy Text Block]	Investments in Qualified Affordable Housing Projects
	The Corporation invests in qualified affordable housing projects solely for the purpose of obtaining tax credits and other tax benefits. Accordingly, the Corporation believes that amortizing its investments in qualified affordable housing projects as a component of income tax expense rather than as a component of operating expenses better reflects the nature and intent of these investments. The Corporation recognized additional income tax expense attributable to the amortization of investments in qualified affordable housing projects of $0.1 million during each of the three months ended March 31, 2015 and 2014. The Corporation's remaining investment in qualified affordable housing projects totaled $4.8 million at March 31, 2015, $4.9 million at December 31, 2014 and $3.2 million at March 31, 2014.
Shareholders' Equity	Shareholders’ 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 March 31, 2015, there were 500,000 remaining shares available for repurchase under the Corporation’s stock repurchase program.
	Underwritten Public Offerings of Common Stock
	On June 24, 2014, the Corporation issued and sold 2,500,000 shares of common stock at a public offering price of $28.00 per share. An additional 375,000 shares were issued and sold on June 30, 2014 upon the exercise in full of the underwriters' over-allotment option. The net proceeds from the issuance and sale of the common stock of this $80.5 million offering, after deducting the underwriting discount and issuance-related expenses, totaled $76.2 million.
	On September 18, 2013, the Corporation issued and sold 2,213,750 shares of common stock, including 288,750 shares of common stock that were issued and sold upon the exercise in full of the underwriters' over-allotment option, at a public offering price of $26.00 per share. The net proceeds from the issuance and sale of the common stock, after deducting the underwriting discount and issuance-related expenses, totaled $53.9 million.
	Shelf Registration
	On June 12, 2014, the Corporation filed an automatic shelf registration statement on Form S-3 with the Securities and Exchange Commission (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, 2009, the shareholders of the Corporation authorized the board of directors of the Corporation to issue up to 200,000 shares of preferred stock in connection with either an acquisition by the Corporation of an entity that has shares of preferred stock issued and outstanding pursuant to any program established by the United States government or participation by the Corporation in any program established by the United States government. On April 20, 2015, the shareholders of the Corporation approved an amendment to the restated articles of incorporation which eliminates and replaces the previous class of 200,000 shares of preferred stock with a new class of 2,000,000 shares of preferred stock. At March 31, 2015, no shares of preferred stock were issued and outstanding.
	Common Stock
	On April 20, 2015, 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 45,000,000 to 60,000,000.
Legal Matters	Legal Matters
	The Corporation and Chemical Bank are subject to certain legal actions arising in the ordinary course of business. In the opinion of management, after consultation with legal counsel, the ultimate disposition of these matters is not expected to have a material adverse effect on the consolidated financial condition or results of operations of the Corporation.
Adopted Accounting Pronouncements	Adopted Accounting Pronouncements
	In-Substance Foreclosures
	In January 2014, the FASB issued ASU 2014-04, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40): Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-04). ASU 2014-04 clarifies that an in-substance foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (i) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (ii) the borrower conveying all interest in the residential real estate property to the creditor to satisfy the loan through completion of a deed in lieu of foreclosure or similar legal agreement. ASU 2014-04 also requires disclosure of both the amount of foreclosed residential real estate property held by the creditor and the recorded investment in loans collateralized by residential real estate property that are in the process of foreclosure. ASU 2014-04 is effective for public companies for interim and annual periods beginning after December 15, 2014, with early adoption permitted. Once adopted, an entity can elect either (i) a modified retrospective transition method or (ii) a prospective transition method. The modified retrospective transition method is applied by means of a cumulative-effect adjustment to residential mortgage loans and foreclosed residential real estate properties existing as of the beginning of the period for which the amendments of ASU 2014-04 are effective, with real estate reclassified to loans measured at the carrying value of the real estate at the date of adoption and loans reclassified to real estate measured at the lower of net carrying value of the loan or the fair value of the real estate less costs to sell at the date of adoption. The prospective transition method is applied by means of applying the amendments of ASU 2014-04 to all instances of receiving physical possession of residential real estate properties that occur after the date of adoption. The adoption of ASU 2014-04 on January 1, 2015 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
	Share-Based Compensation
	In June 2014, the FASB issued ASU 2014-12, Compensation—Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period, a consensus of the FASB Emerging Issues Task Force (ASU 2014-12). ASU 2014-12 requires that a performance target that affects vesting of share-based payment awards and that could be achieved after the requisite service period be treated as a performance condition. Compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which the requisite service has already been rendered. If the performance target becomes probable of being achieved before the end of the requisite service period, the remaining unrecognized compensation cost should be recognized prospectively over the remaining requisite service period. The total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest and should be adjusted to reflect those awards that ultimately vest. The requisite service period ends when the employee can cease rendering service and still be eligible to vest in the award if the performance target is achieved. ASU 2014-12 is effective for all entities for interim and annual periods beginning after December 15, 2015, with early adoption permitted. An entity may apply the amendments in ASU 2014-12 either (i) prospectively to all awards granted or modified after the effective date or (ii) retrospectively to all awards with performance targets that are outstanding as of the beginning of the earliest annual period presented in the financial statements and to all new or modified awards thereafter. The Corporation's early adoption of ASU 2014-12 on January 1, 2015 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
	Government-Guaranteed Mortgage Loans
	In August 2014, the FASB issued ASU 2014-14, Receivables-Troubled Debt Restructurings by Creditors (Subtopic 310-40): Classification of Certain Government Guaranteed Mortgage Loans upon Foreclosure, a consensus of the FASB Emerging Issues Task Force (ASU 2014-14). ASU 2014-14 provides clarifying guidance related to how creditors classify government-guaranteed loans upon foreclosure. Upon foreclosure of a government-guaranteed mortgage loan, the loan should be derecognized and a separate other receivable should be recognized if the following conditions are met: (i) the loan has a government guarantee that is not separable from the loan before foreclosure; (ii) at the time of foreclosure, the creditor has the intent to convey the real estate property to the guarantor and make a claim on the guarantee, and the creditor has the ability to recover under that claim; and (iii) at the time of foreclosure, any amount of the claim that is determined on the basis of the fair value of the real estate is fixed. The separate other receivable should be measured based on the amount of the loan balance (principal and interest) expected to be recovered from the guarantor at the time of foreclosure. ASU 2014-14 is effective for public companies for interim and annual periods beginning after December 15, 2014. An entity should adopt using either the modified retrospective method or the prospective transition method. An entity must apply the same method elected under ASU 2014-04. Early adoption is permitted if the entity has already adopted ASU 2014-04. The adoption of ASU 2014-14 on January 1, 2015 did not have a material impact on the Corporation's consolidated financial condition or results of operations.
Pending Accounting Pronouncements	Pending Accounting Pronouncements
	There are no recent accounting pronouncements that have been issued by the FASB that would have a material impact on the financial statements of the Corporation.

Acquisitions_Tables

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Activity for accretable yield includes contractually due interest of acquired loans	Activity for the accretable yield, which includes contractually due interest for acquired loans that have been renewed or extended since the date of acquisition and continue to be accounted for in loan pools in accordance with ASC 310-30, follows:
			Three Months Ended March 31,
			2015									2014
			Northwestern			OAK			Total			OAK
			(In thousands)
	Balance at beginning of period		$	104,675		$	33,286		137,961			$	32,610
	Additions (reductions)*		(1,410		)	714			(696		)	821
	Accretion recognized in interest income		(4,998		)	(3,207		)	(8,205		)	(3,843		)
	Reclassification from nonaccretable difference		—			—			—			10,000
	Balance at end of period		$	98,267		$	30,793		$	129,060		$	39,588
	*	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.

Investment_Securities_Tables

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015, December 31, 2014 and March 31, 2014:
		Investment Securities Available-for-Sale
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	31-Mar-15
	U.S. Treasury securities	$	8,271	$	31	$	—	$	8,302
	Government sponsored agencies	249,642		889		101		250,430
	State and political subdivisions	31,701		624		3		32,322
	Residential mortgage-backed securities	218,299		1,358		56		219,601
	Collateralized mortgage obligations	133,713		305		718		133,300
	Corporate bonds	34,925		136		64		34,997
	Preferred stock	1,389		303		—		1,692
	Total	$	677,940	$	3,646	$	942	$	680,644
	31-Dec-14
	U.S. Treasury securities	$	8,272	$	—	$	13	$	8,259
	Government sponsored agencies	263,658		356		511		263,503
	State and political subdivisions	45,157		1,087		17		46,227
	Residential mortgage-backed securities	240,465		885		1,543		239,807
	Collateralized mortgage obligations	145,316		261		1,194		144,383
	Corporate bonds	44,930		213		48		45,095
	Preferred stock	1,389		201		—		1,590
	Total	$	749,187	$	3,003	$	3,326	$	748,864
	31-Mar-14
	Government sponsored agencies	$	91,613	$	295	$	298	$	91,610
	State and political subdivisions	42,369		1,408		—		43,777
	Residential mortgage-backed securities	291,187		1,023		3,472		288,738
	Collateralized mortgage obligations	167,622		393		1,296		166,719
	Corporate bonds	65,003		505		93		65,415
	Preferred stock	1,389		170		—		1,559
	Total	$	659,183	$	3,794	$	5,159	$	657,818
Held-to-maturity Securities
		Investment Securities Held-to-Maturity
		Amortized		Unrealized		Unrealized		Fair
		Cost		Gains		Losses		Value
		(In thousands)
	31-Mar-15
	State and political subdivisions	$	370,950	$	6,852	$	4,926	$	372,876
	Trust preferred securities	10,500		—		3,200		7,300
	Total	$	381,450	$	6,852	$	8,126	$	380,176
	31-Dec-14
	State and political subdivisions	$	305,913	$	7,294	$	4,557	$	308,650
	Trust preferred securities	10,500		—		3,410		7,090
	Total	$	316,413	$	7,294	$	7,967	$	315,740
	31-Mar-14
	State and political subdivisions	$	267,599	$	5,331	$	6,983	$	265,947
	Trust preferred securities	10,500		—		4,040		6,460
	Total	$	278,099	$	5,331	$	11,023	$	272,407
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 March 31, 2015, 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.
		31-Mar-15
		Amortized		Fair Value
		Cost
		(In thousands)
	Investment Securities Available-for-Sale:
	Due in one year or less	$	180,558	$	180,869
	Due after one year through five years	442,088		443,752
	Due after five years through ten years	50,902		51,302
	Due after ten years	3,003		3,029
	Preferred stock	1,389		1,692
	Total	$	677,940	$	680,644
	Investment Securities Held-to-Maturity:
	Due in one year or less	$	35,293	$	35,365
	Due after one year through five years	171,557		172,699
	Due after five years through ten years	120,799		122,512
	Due after ten years	53,801		49,600
	Total	$	381,450	$	380,176
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 March 31, 2015, December 31, 2014 and March 31, 2014, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position.
		Less Than 12 Months				12 Months or More				Total
		Fair		Gross		Fair		Gross		Fair		Gross
		Value		Unrealized		Value		Unrealized		Value		Unrealized
				Losses				Losses				Losses
		(In thousands)
	31-Mar-15
	U.S. Treasury securities	$	—	$	—	$	—	$	—	$	—	$	—
	Government sponsored agencies	27,889		64		18,896		37		46,785		101
	State and political subdivisions	156,010		1,989		49,839		2,940		205,849		4,929
	Residential mortgage-backed securities	82,303		28		3,847		28		86,150		56
	Collateralized mortgage obligations	22,694		22		41,061		696		63,755		718
	Corporate bonds	4,989		11		14,946		53		19,935		64
	Trust preferred securities	—		—		7,300		3,200		7,300		3,200
	Total	$	293,885	$	2,114	$	135,889	$	6,954	$	429,774	$	9,068
	31-Dec-14
	U.S. Treasury securities	$	8,259	$	13	$	—	$	—	$	8,259	$	13
	Government sponsored agencies	166,963		406		31,927		105		198,890		511
	State and political subdivisions	62,310		3,348		36,847		1,226		99,157		4,574
	Residential mortgage-backed securities	17,276		52		180,194		1,491		197,470		1,543
	Collateralized mortgage obligations	63,077		179		31,620		1,015		94,697		1,194
	Corporate bonds	—		—		14,952		48		14,952		48
	Trust preferred securities	—		—		7,090		3,410		7,090		3,410
	Total	$	317,885	$	3,998	$	302,630	$	7,295	$	620,515	$	11,293
	31-Mar-14
	Government sponsored agencies	$	45,396	$	110	$	15,204	$	188	$	60,600	$	298
	State and political subdivisions	79,787		4,942		56,180		2,041		135,967		6,983
	Residential mortgage-backed securities	247,397		3,472		—		—		247,397		3,472
	Collateralized mortgage obligations	76,900		885		12,833		411		89,733		1,296
	Corporate bonds	—		—		14,907		93		14,907		93
	Trust preferred securities	—		—		6,460		4,040		6,460		4,040
	Total	$	449,480	$	9,409	$	105,584	$	6,773	$	555,064	$	16,182

Loans_Tables

Loans (Tables)	3 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Summary of loans under portfolio	A summary of loans follows:
			March 31,				December 31,				March 31,
			2015				2014				2014
			(In thousands)
	Commercial loan portfolio:
	Commercial		$	1,356,169			$	1,354,881			$	1,208,641
	Commercial real estate		1,616,923				1,557,648				1,279,167
	Real estate construction		95,923				152,745				85,084
	Land development		12,916				18,750				13,761
	Subtotal		3,081,931				3,084,024				2,586,653
	Consumer loan portfolio:
	Residential mortgage		1,117,445				1,110,390				962,009
	Consumer installment		844,066				829,570				675,412
	Home equity		659,432				664,246				529,215
	Subtotal		2,620,943				2,604,206				2,166,636
	Total loans		$	5,702,874			$	5,688,230			$	4,753,289
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 risk rating categories at March 31, 2015, December 31, 2014 and March 31, 2014:
			Commercial				Commercial Real Estate				Real Estate			Land			Total
											Construction			Development
			(In thousands)
	31-Mar-15
	Originated Portfolio:
	Risk Grades 1-5		$	1,176,021			$	1,175,373			$	93,864		$	2,633		$	2,447,891
	Risk Grade 6		40,999				44,248				—			738			85,985
	Risk Grade 7		28,983				27,961				1,396			601			58,941
	Risk Grade 8		18,904				24,760				663			290			44,617
	Risk Grade 9		—				6				—			—			6
	Subtotal		1,264,907				1,272,348				95,923			4,262			2,637,440
	Acquired Portfolio:
	Risk Grades 1-5		71,422				318,113				—			6,724			396,259
	Risk Grade 6		11,299				7,786				—			253			19,338
	Risk Grade 7		6,509				12,735				—			140			19,384
	Risk Grade 8		2,032				5,941				—			1,537			9,510
	Risk Grade 9		—				—				—			—			—
	Subtotal		91,262				344,575				—			8,654			444,491
	Total		$	1,356,169			$	1,616,923			$	95,923		$	12,916		$	3,081,931
	31-Dec-14
	Originated Portfolio:
	Risk Grades 1-5		$	1,171,817			$	1,114,529			$	134,668		$	2,952		$	2,423,966
	Risk Grade 6		37,800				34,996				1,408			738			74,942
	Risk Grade 7		29,863				29,935				2,502			613			62,913
	Risk Grade 8		16,417				24,958				162			225			41,762
	Risk Grade 9		1				8				—			—			9
	Subtotal		1,255,898				1,204,426				138,740			4,528			2,603,592
	Acquired Portfolio:
	Risk Grades 1-5		76,780				321,018				14,005			11,789			423,592
	Risk Grade 6		12,687				8,698				—			583			21,968
	Risk Grade 7		4,089				12,478				—			197			16,764
	Risk Grade 8		5,427				11,028				—			1,653			18,108
	Risk Grade 9		—				—				—			—			—
	Subtotal		98,983				353,222				14,005			14,222			480,432
	Total		$	1,354,881			$	1,557,648			$	152,745		$	18,750		$	3,084,024
	31-Mar-14
	Originated Portfolio:
	Risk Grades 1-5		$	1,060,743			$	1,034,517			$	70,750		$	3,831		$	2,169,841
	Risk Grade 6		18,359				33,962				680			968			53,969
	Risk Grade 7		33,768				32,671				815			700			67,954
	Risk Grade 8		17,301				27,552				160			2,267			47,280
	Risk Grade 9		950				16				—			—			966
	Subtotal		1,131,121				1,128,718				72,405			7,766			2,340,010
	Acquired Portfolio:
	Risk Grades 1-5		67,326				139,130				12,679			3,906			223,041
	Risk Grade 6		2,423				2,627				—			—			5,050
	Risk Grade 7		3,635				7,753				—			—			11,388
	Risk Grade 8		4,136				939				—			2,089			7,164
	Risk Grade 9		—				—				—			—			—
	Subtotal		77,520				150,449				12,679			5,995			246,643
	Total		$	1,208,641			$	1,279,167			$	85,084		$	13,761		$	2,586,653
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 March 31, 2015, December 31, 2014 and March 31, 2014:
			Residential Mortgage				Consumer				Home Equity			Total
							Installment							Consumer
			(In thousands)
	31-Mar-15
	Originated Loans:
	Performing		$	998,196			$	834,926			$	565,992		$	2,399,114
	Nonperforming		9,376				433				2,299			12,108
	Subtotal		1,007,572				835,359				568,291			2,411,222
	Acquired Loans:
	Performing		109,005				8,696				90,686			208,387
	Nonperforming		868				11				455			1,334
	Subtotal		109,873				8,707				91,141			209,721
	Total		$	1,117,445			$	844,066			$	659,432		$	2,620,943
	31-Dec-14
	Originated Loans:
	Performing		$	987,542			$	818,878			$	566,083		$	2,372,503
	Nonperforming		10,459				500				3,013			13,972
	Subtotal		998,001				819,378				569,096			2,386,475
	Acquired Loans:
	Performing		111,101				10,174				94,696			215,971
	Nonperforming		1,288				18				454			1,760
	Subtotal		112,389				10,192				95,150			217,731
	Total		$	1,110,390			$	829,570			$	664,246		$	2,604,206
	31-Mar-14
	Originated Loans:
	Performing		$	937,968			$	672,984			$	497,196		$	2,108,148
	Nonperforming		12,833				806				2,668			16,307
	Subtotal		950,801				673,790				499,864			2,124,455
	Acquired Loans:
	Performing		11,150				1,622				29,020			41,792
	Nonperforming		58				—				331			389
	Subtotal		11,208				1,622				29,351			42,181
	Total		$	962,009			$	675,412			$	529,215		$	2,166,636
Summary of nonperforming loans	A summary of nonperforming loans follows:
			March 31,				December 31,				March 31,
			2015				2014				2014
			(In thousands)
	Nonaccrual loans:
	Commercial		$	18,904			$	16,418			$	18,251
	Commercial real estate		24,766				24,966				27,568
	Real estate construction		663				162				160
	Land development		290				225				2,267
	Residential mortgage		6,514				6,706				6,589
	Consumer installment		433				500				806
	Home equity		1,870				1,667				2,046
	Total nonaccrual loans		53,440				50,644				57,687
	Accruing loans contractually past due 90 days or more as to interest or principal payments:
	Commercial		52				170				43
	Commercial real estate		148				—				730
	Real estate construction		—				—				—
	Land development		—				—				—
	Residential mortgage		172				557				—
	Consumer installment		—				—				—
	Home equity		429				1,346				622
	Total accruing loans contractually past due 90 days or more as to interest or principal payments		801				2,073				1,395
	Nonperforming TDRs:
	Commercial loan portfolio		15,810				15,271				11,218
	Consumer loan portfolio		2,690				3,196				6,244
	Total nonperforming TDRs		18,500				18,467				17,462
	Total nonperforming loans		$	72,741			$	71,184			$	76,544
Schedule of Impaired loans by classes	The following schedule presents impaired loans by classes of loans at March 31, 2015, December 31, 2014 and March 31, 2014:
			Recorded				Unpaid				Related
			Investment				Principal				Valuation
							Balance				Allowance
			(In thousands)
	31-Mar-15
	Impaired loans with a valuation allowance:
	Commercial		$	3,433			$	3,527			$	1,119
	Commercial real estate		1,780				1,961				496
	Real estate construction		—				—				—
	Land development		—				—				—
	Residential mortgage		19,887				19,887				297
	Subtotal		25,100				25,375				1,912
	Impaired loans with no related valuation allowance:
	Commercial		33,733				39,382				—
	Commercial real estate		57,628				79,696				—
	Real estate construction		663				836				—
	Land development		1,877				3,428				—
	Residential mortgage		7,382				7,382				—
	Consumer installment		444				444				—
	Home equity		2,325				2,325				—
	Subtotal		104,052				133,493				—
	Total impaired loans:
	Commercial		37,166				42,909				1,119
	Commercial real estate		59,408				81,657				496
	Real estate construction		663				836				—
	Land development		1,877				3,428				—
	Residential mortgage		27,269				27,269				297
	Consumer installment		444				444				—
	Home equity		2,325				2,325				—
	Total		$	129,152			$	158,868			$	1,912
	31-Dec-14
	Impaired loans with a valuation allowance:
	Commercial		$	966			$	1,040			$	293
	Commercial real estate		2,587				2,927				710
	Real estate construction		—				—				—
	Land development		—				—				—
	Residential mortgage		19,681				19,681				335
	Subtotal		23,234				23,648				1,338
	Impaired loans with no related valuation allowance:
	Commercial		38,094				44,557				—
	Commercial real estate		60,616				82,693				—
	Real estate construction		162				255				—
	Land development		1,928				3,484				—
	Residential mortgage		7,994				7,994				—
	Consumer installment		518				518				—
	Home equity		2,121				2,121				—
	Subtotal		111,433				141,622				—
	Total impaired loans:
	Commercial		39,060				45,597				293
	Commercial real estate		63,203				85,620				710
	Real estate construction		162				255				—
	Land development		1,928				3,484				—
	Residential mortgage		27,675				27,675				335
	Consumer installment		518				518				—
	Home equity		2,121				2,121				—
	Total		$	134,667			$	165,270			$	1,338
			Recorded				Unpaid				Related
			Investment				Principal				Valuation
							Balance				Allowance
			(In thousands)
	31-Mar-14
	Impaired loans with a valuation allowance:
	Commercial		$	3,534			$	3,704			$	1,250
Commercial real estate		3,720				3,878				371
Real estate construction		—				—				—
Land development		—				—				—
Residential mortgage		19,944				19,944				444
Subtotal		27,198				27,526				2,065
Impaired loans with no related valuation allowance:
Commercial		38,150				42,914				—
Commercial real estate		49,074				62,207				—
Real estate construction		160				366				—
Land development		4,472				7,773				—
Residential mortgage		6,589				6,589				—
Consumer installment		806				806				—
Home equity		2,046				2,046				—
Subtotal		101,297				122,701				—
Total impaired loans:
Commercial		41,684				46,618				1,250
Commercial real estate		52,794				66,085				371
Real estate construction		160				366				—
Land development		4,472				7,773				—
Residential mortgage		26,533				26,533				444
Consumer installment		806				806				—
Home equity		2,046				2,046				—
Total		$	128,495			$	150,227			$	2,065
Schedule presents information related to impaired loans	The following schedule presents information related to impaired loans for the three months ended March 31, 2015 and 2014:
			Three Months Ended March 31, 2015
			Average				Interest Income
			Recorded				Recognized
			Investment				While on
							Impaired Status
			(In thousands)
	Commercial		$	38,576			$	289
	Commercial real estate		60,240				525
	Real estate construction		640				—
	Land development		1,875				27
	Residential mortgage		27,352				331
	Consumer installment		499				—
	Home equity		2,352				8
	Total		$	131,534			$	1,180
			Three Months Ended March 31, 2014
			Average				Interest Income
			Recorded				Recognized
			Investment				While on
							Impaired Status
			(In thousands)
	Commercial		$	41,607			$	333
	Commercial real estate		53,320				361
	Real estate construction		167				—
	Land development		4,643				37
	Residential mortgage		26,781				303
	Consumer installment		773				—
	Home equity		2,168				—
	Total		$	129,459			$	1,034
Schedule representing the aging status of the recorded investment in loans by classes	The following schedule presents the aging status of the recorded investment in loans by classes of loans at March 31, 2015, December 31, 2014 and March 31, 2014:
			31-60				61-89				Accruing			Non-accrual			Total		Current		Total
			Days				Days				Loans			Loans			Past Due				Loans
			Past Due				Past Due				Past Due
											90 Days
											or More
			(In thousands)
	31-Mar-15
	Originated Portfolio:
	Commercial		$	10,121			$	729			$	52		$	18,904		$	29,806	$	1,235,101	$	1,264,907
	Commercial real estate		7,238				2,267				148			24,766			34,419		1,237,929		1,272,348
	Real estate construction		340				—				—			663			1,003		94,920		95,923
	Land development		—				—				—			290			290		3,972		4,262
	Residential mortgage		1,246				88				172			6,514			8,020		999,552		1,007,572
	Consumer installment		2,143				344				—			433			2,920		832,439		835,359
	Home equity		1,728				197				429			1,870			4,224		564,067		568,291
	Total		$	22,816			$	3,625			$	801		$	53,440		$	80,682	$	4,967,980	$	5,048,662
	Acquired Portfolio:
	Commercial		$	59			$	5			$	2,089		$	—		$	2,153	$	89,109	$	91,262
	Commercial real estate		1,784				138				6,271			—			8,193		336,382		344,575
	Real estate construction		—				—				—			—			—		—		—
	Land development		—				—				1,537			—			1,537		7,117		8,654
	Residential mortgage		104				—				868			—			972		108,901		109,873
	Consumer installment		3				1				11			—			15		8,692		8,707
	Home equity		349				234				455			—			1,038		90,103		91,141
	Total		$	2,299			$	378			$	11,231		$	—		$	13,908	$	640,304	$	654,212
			31-60				61-89				Accruing			Non-accrual			Total		Current		Total
			Days				Days				Loans			Loans			Past Due				Loans
			Past Due				Past Due				Past Due
											90 Days
											or More
			(In thousands)
	31-Dec-14
	Originated Portfolio:
	Commercial		$	4,033			$	743			$	170		$	16,418		$	21,364	$	1,234,534	$	1,255,898
	Commercial real estate		7,515				1,383				—			24,966			33,864		1,170,562		1,204,426
	Real estate construction		262				—				—			162			424		138,316		138,740
	Land development		—				—				—			225			225		4,303		4,528
	Residential mortgage		2,126				54				557			6,706			9,443		988,558		998,001
	Consumer installment		3,620				512				—			500			4,632		814,746		819,378
	Home equity		3,039				660				1,346			1,667			6,712		562,384		569,096
	Total		$	20,595			$	3,352			$	2,073		$	50,644		$	76,664	$	4,913,403	$	4,990,067
	Acquired Portfolio:
	Commercial		$	133			$	—			$	5,427		$	—		$	5,560	$	93,423	$	98,983
	Commercial real estate		2,014				352				11,052			—			13,418		339,804		353,222
	Real estate construction		—				—				—			—			—		14,005		14,005
	Land development		—				—				1,653			—			1,653		12,569		14,222
	Residential mortgage		156				—				18			—			174		112,215		112,389
	Consumer installment		55				3				454			—			512		9,680		10,192
	Home equity		636				106				1,288			—			2,030		93,120		95,150
	Total		$	2,994			$	461			$	19,892		$	—		$	23,347	$	674,816	$	698,163
	31-Mar-14
	Originated Portfolio:
	Commercial		$	6,003			$	1,832			$	43		$	18,251		$	26,129	$	1,104,992	$	1,131,121
	Commercial real estate		4,094				1,098				730			27,568			33,490		1,095,228		1,128,718
	Real estate construction		18				—				—			160			178		72,227		72,405
	Land development		—				—				—			2,267			2,267		5,499		7,766
	Residential mortgage		1,259				1,138				—			6,589			8,986		941,815		950,801
	Consumer installment		1,950				313				—			806			3,069		670,721		673,790
	Home equity		1,500				256				622			2,046			4,424		495,440		499,864
	Total		$	14,824			$	4,637			$	1,395		$	57,687		$	78,543	$	4,385,922	$	4,464,465
	Acquired Portfolio:
	Commercial		$	—			$	—			$	6,496		$	—		$	6,496	$	71,024	$	77,520
	Commercial real estate		—				—				2,549			—			2,549		147,900		150,449
Real estate construction		—				—				—			—			—		12,679		12,679
Land development		—				—				2,089			—			2,089		3,906		5,995
Residential mortgage		—				—				58			—			58		11,150		11,208
Consumer installment		49				—				—			—			49		1,573		1,622
Home equity		49				—				331			—			380		28,971		29,351
Total		$	98			$	—			$	11,523		$	—		$	11,621	$	277,203	$	288,824
Schedule of Corporation's TDRs	The following schedule presents the Corporation’s loans reported as TDRs at March 31, 2015, December 31, 2014 and March 31, 2014:
			Performing TDRs				Non-Performing TDRs				Nonaccrual TDRs			Total
			(In thousands)
	31-Mar-15
	Commercial loan portfolio		$	28,784			$	15,810			$	32,917		$	77,511
	Consumer loan portfolio		17,197				2,690				4,426			24,313
	Total		$	45,981			$	18,500			$	37,343		$	101,824
	31-Dec-14
	Commercial loan portfolio		$	29,179			$	15,271			$	32,597		$	77,047
	Consumer loan portfolio		16,485				3,196				4,594			24,275
	Total		$	45,664			$	18,467			$	37,191		$	101,322
	31-Mar-14
	Commercial loan portfolio		$	28,123			$	11,218			$	40,511		$	79,852
	Consumer loan portfolio		13,700				6,244				3,875			23,819
	Total		$	41,823			$	17,462			$	44,386		$	103,671
Schedule providing information on TDRs	The following schedule provides information on the Corporation's TDRs that were modified during the three months ended March 31, 2015 and 2014:
		Number			Pre-				Post-
		of Loans			Modification				Modification
					Recorded				Recorded
					Investment				Investment
		(Dollars in thousands)
	Three Months Ended March 31, 2015
	Commercial loan portfolio:
	Commercial	5			$	1,932			$	1,932
	Commercial real estate	5			2,534				2,534
	Land development	—			—				—
	Subtotal – commercial loan portfolio	10			4,466				4,466
	Consumer loan portfolio	10			336				336
	Total	20			$	4,802			$	4,802
	Three Months Ended March 31, 2014
	Commercial loan portfolio:
	Commercial	12			$	8,356			$	8,356
	Commercial real estate	9			2,790				2,790
	Real estate construction	—			—				—
	Land development	1			72				72
	Subtotal – commercial loan portfolio	22			11,218				11,218
	Consumer loan portfolio	30			987				978
	Total	52			$	12,205			$	12,196
Troubled debt restructurings on financing receivables with defaults payment	The following schedule includes TDRs for which there was a payment default during the three months ended March 31, 2015 and 2014, 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:
			Number of			Principal Balance at End of Period
			Loans
			(Dollars in thousands)
	Three Months Ended March 31, 2015
	Commercial loan portfolio:
	Commercial		—			$	—
	Commercial real estate		3			759
	Subtotal – commercial loan portfolio		3			759
	Consumer loan portfolio		1			33
	Total		4			$	792
	Three Months Ended March 31, 2014
	Commercial loan portfolio:
	Commercial		1			$	104
	Commercial real estate		2			1,670
	Real estate construction		—			—
	Land development		—			—
	Subtotal – commercial loan portfolio		3			1,774
	Consumer loan portfolio		—			—
	Total		3			$	1,774
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment	The following schedule presents, by loan portfolio segment, the changes in the allowance for the three months ended March 31, 2015 and details regarding the balance in the allowance and the recorded investment in loans at March 31, 2015 by impairment evaluation method.
			Commercial				Consumer				Unallocated			Total
			Loan				Loan
			Portfolio				Portfolio
			(In thousands)
	Changes in allowance for loan losses for the three months ended March 31, 2015:
	Beginning balance		$	44,156			$	28,803			$	2,724		$	75,683
	Provision for loan losses		3,593				(3,227		)		1,134			1,500
	Charge-offs		(1,504		)		(1,639		)		—			(3,143		)
	Recoveries		574				642				—			1,216
	Ending balance		$	46,819			$	24,579			$	3,858		$	75,256
	Allowance for loan losses balance at March 31, 2015 attributable to:
	Loans individually evaluated for impairment		$	1,615			$	297			$	—		$	1,912
	Loans collectively evaluated for impairment		45,204				24,282				3,858			73,344
	Loans acquired with deteriorated credit quality		—				—				—			—
	Total		$	46,819			$	24,579			$	3,858		$	75,256
	Recorded investment (loan balance) at March 31, 2015:
	Loans individually evaluated for impairment		$	89,217			$	19,887			$	—		$	109,104
	Loans collectively evaluated for impairment		2,548,223				2,391,335				—			4,939,558
	Loans acquired with deteriorated credit quality		444,491				209,721				—			654,212
	Total		$	3,081,931			$	2,620,943			$	—		$	5,702,874
	The following schedule presents, by loan portfolio segment, details regarding the balance in the allowance and the recorded investment in loans at December 31, 2014 by impairment evaluation method.
			Commercial				Consumer				Unallocated			Total
			Loan				Loan
			Portfolio				Portfolio
			(In thousands)
	Allowance for loan losses balance at December 31, 2014 attributable to:
	Loans individually evaluated for impairment		$	1,003			$	335			$	—		$	1,338
	Loans collectively evaluated for impairment		43,153				27,968				2,724			73,845
	Loans acquired with deteriorated credit quality		—				500				—			500
	Total		$	44,156			$	28,803			$	2,724		$	75,683
	Recorded investment (loan balance) at December 31, 2014:
	Loans individually evaluated for impairment		$	86,221			$	19,681			$	—		$	105,902
	Loans collectively evaluated for impairment		2,517,371				2,366,794				—			4,884,165
	Loans acquired with deteriorated credit quality		480,432				217,731				—			698,163
	Total		$	3,084,024			$	2,604,206			$	—		$	5,688,230
	The following schedule presents, by loan portfolio segment, the changes in the allowance for the three months ended March 31, 2014 and details regarding the balance in the allowance and the recorded investment in loans at March 31, 2014 by impairment evaluation method.
			Commercial				Consumer				Unallocated			Total
			Loan				Loan
			Portfolio				Portfolio
			(In thousands)
	Changes in allowance for loan losses for the three months ended March 31, 2014:
	Beginning balance		$	44,482			$	30,145			$	4,445		$	79,072
	Provision for loan losses		960				855				(215		)	1,600
	Charge-offs		(1,209		)		(2,263		)		—			(3,472		)
	Recoveries		777				496				—			1,273
	Ending balance		$	45,010			$	29,233			$	4,230		$	78,473
	Allowance for loan losses balance at March 31, 2014 attributable to:
	Loans individually evaluated for impairment		$	1,621			$	444			$	—		$	2,065
	Loans collectively evaluated for impairment		43,389				28,289				4,230			75,908
	Loans acquired with deteriorated credit quality		—				500				—			500
	Total		$	45,010			$	29,233			$	4,230		$	78,473
	Recorded investment (loan balance) at March 31, 2014:
	Loans individually evaluated for impairment		$	87,587			$	19,944			$	—		$	107,531
	Loans collectively evaluated for impairment		2,252,423				2,104,511				—			4,356,934
	Loans acquired with deteriorated credit quality		246,643				42,181				—			288,824
	Total		$	2,586,653			$	2,166,636			$	—		$	4,753,289

Intangible_Assets_Tables

Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Net carrying value of intangible assets	The following table shows the net carrying value of the Corporation’s intangible assets:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Goodwill	$	180,128		$	180,128		$	120,164
	Other intangible assets:
	Core deposit intangible assets	$	20,072		$	20,863		$	9,556
	Mortgage servicing rights	11,583			12,217			3,316
	Total other intangible assets	$	31,655		$	33,080		$	12,872
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets	The following table sets forth the carrying amount, accumulated amortization and amortization expense of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Gross original amount	$	30,122		$	31,550		$	18,659
	Accumulated amortization	10,050			10,687			9,103
	Carrying amount	$	20,072		$	20,863		$	9,556
	Amortization expense for the three months ended March 31	$	791					$	445
Net carrying value, fair value of MSRs and loans Corporation servicing for others	The following shows the net carrying value and fair value of MSRs and the total loans that the Corporation is servicing for others:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Net carrying value of MSRs	$	11,583		$	12,217		$	3,316
	Fair value of MSRs	$	14,378		$	14,979		$	6,706
	Loans serviced for others that have servicing rights capitalized	$	2,062,544		$	2,093,140		$	877,530
Activity for capitalized MSRs	The following table shows the activity for capitalized MSRs:
		Three Months Ended March 31,
		2015			2014
		(In thousands)
	Balance at beginning of period	$	12,217		$	3,423
	Additions	400			143
	Amortization	(1,034		)	(250		)
	Balance at end of period	$	11,583		$	3,316

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Components of accumulated other comprehensive loss, net of related tax benefit/expense	The components of accumulated other comprehensive loss, net of related tax benefit/expense, were as follows:
		March 31,			December 31,			March 31,
		2015			2014			2014
		(In thousands)
	Net unrealized gains (losses) on investment securities – available-for-sale, net of related tax expense (benefit) of $946 at March 31, 2015, $(113) at December 31, 2014 and $(478) at March 31, 2014	$	1,758		$	(210	)	$	(887	)
	Pension and other postretirement benefits adjustment, net of related tax benefit of $16,981 at March 31, 2015, $17,362 at December 31, 2014 and $9,915 at March 31, 2014	(31,537		)	(32,243		)	(18,414		)
	Accumulated other comprehensive loss	$	(29,779	)	$	(32,453	)	$	(19,301	)

Regulatory_Capital_Tables

Regulatory Capital (Tables)	3 Months Ended
	Mar. 31, 2015
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 Corporation’s and Chemical Bank’s actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy:
		Actual				Minimum Required for Capital Adequacy Purposes				Required to be Well Capitalized Under Prompt Corrective Action Regulations
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
		(Dollars in thousands)
	31-Mar-15
	Total Capital to Risk-Weighted Assets:
	Corporation	$	727,090	13	%	$	446,173	8	%	N/A		N/A
	Chemical Bank	676,488		12.1		445,471		8		$	556,838	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	657,307		11.8		334,630		6		N/A		N/A
	Chemical Bank	606,813		10.9		334,103		6		445,471		8
	Common Equity Tier 1 Capital to Risk-Weighted Assets:
	Corporation	657,307		11.8		250,972		4.5		N/A		N/A
	Chemical Bank	606,813		10.9		250,577		4.5		361,945		6.5
	Leverage Ratio:
	Corporation	657,307		9.1		289,948		4		N/A		N/A
	Chemical Bank	606,813		8.4		289,840		4		362,300		5
	31-Dec-14
	Total Capital to Risk-Weighted Assets:
	Corporation	$	705,130	12.4	%	$	456,302	8	%	N/A		N/A
	Chemical Bank	654,031		11.5		455,633		8		$	569,541	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	633,779		11.1		228,151		4		N/A		N/A
	Chemical Bank	582,783		10.2		227,816		4		341,725		6
	Leverage Ratio:
	Corporation	633,779		9.3		273,226		4		N/A		N/A
	Chemical Bank	582,783		8.5		273,048		4		341,310		5
	31-Mar-14
	Total Capital to Risk-Weighted Assets:
	Corporation	$	659,644	13.8	%	$	381,146	8	%	N/A		N/A
	Chemical Bank	589,254		12.4		380,542		8		$	475,678	10	%
	Tier 1 Capital to Risk-Weighted Assets:
	Corporation	599,856		12.6		190,573		4		N/A		N/A
	Chemical Bank	529,560		11.1		190,271		4		285,407		6
	Leverage Ratio:
	Corporation	599,856		9.9		243,070		4		N/A		N/A
	Chemical Bank	529,560		8.7		242,939		4		303,673		5

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Summary of assets measured at fair value on a recurring basis	For assets measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements for each major category of assets were as follows:
			Fair Value Measurements – Recurring Basis
			Quoted Prices			Significant			Significant			Total
			In Active			Other			Unobservable
			Markets for			Observable			Inputs
			Identical			Inputs			(Level 3)
			Assets			(Level 2)
			(Level 1)
			(In thousands)
	31-Mar-15
	Investment securities – available-for-sale:
	U.S. Treasury securities		$	8,302		$	—		$	—		$	8,302
	Government sponsored agencies		—			250,430			—			250,430
	State and political subdivisions		—			32,322			—			32,322
	Residential mortgage-backed securities		—			219,601			—			219,601
	Collateralized mortgage obligations		—			133,300			—			133,300
	Corporate bonds		—			34,997			—			34,997
	Preferred stock		—			1,692			—			1,692
	Total investment securities – available-for-sale		8,302			672,342			—			680,644
	Loans held-for-sale		—			9,675			—			9,675
	Total assets measured at fair value on a recurring basis		$	8,302		$	682,017		$	—		$	690,319
	31-Dec-14
	Investment securities – available-for-sale:
	U.S. Treasury securities		$	8,259		$	—		$	—		$	8,259
	Government sponsored agencies		—			263,503			—			263,503
	State and political subdivisions		—			46,227			—			46,227
	Residential mortgage-backed securities		—			239,807			—			239,807
	Collateralized mortgage obligations		—			144,383			—			144,383
	Corporate bonds		—			45,095			—			45,095
	Preferred stock		—			1,590			—			1,590
	Total investment securities – available-for-sale		8,259			740,605			—			748,864
	Loans held-for-sale		—			9,128			—			9,128
	Total assets measured at fair value on a recurring basis		$	8,259		$	749,733		$	—		$	757,992
	31-Mar-14
	Investment securities – available-for-sale:
	Government sponsored agencies		$	—		$	91,610		$	—		$	91,610
	State and political subdivisions		—			43,777			—			43,777
	Residential mortgage-backed securities		—			288,738			—			288,738
	Collateralized mortgage obligations		—			166,719			—			166,719
	Corporate bonds		—			65,415			—			65,415
	Preferred stock		—			1,559			—			1,559
	Total investment securities – available-for-sale		—			657,818			—			657,818
	Loans held-for-sale		—			3,814			—			3,814
	Total assets measured at fair value on a recurring basis		$	—		$	661,632		$	—		$	661,632
Summary of assets measured at fair value on a nonrecurring basis	For assets measured at fair value on a nonrecurring basis, quantitative disclosures about fair value measurements for each major category of assets were as follows:
			Fair Value Measurements – Nonrecurring Basis
			Quoted Prices			Significant			Significant			Total
			In Active			Other			Unobservable
			Markets for			Observable			Inputs
			Identical			Inputs			(Level 3)
			Assets			(Level 2)
			(Level 1)
			(In thousands)
	31-Mar-15
	Impaired originated loans		$	—		$	—		$	23,730		$	23,730
	Other real estate/repossessed assets		—			—			14,744			14,744
	Mortgage servicing rights		—			—			8,115			8,115
	Total		$	—		$	—		$	46,589		$	46,589
	31-Dec-14
	Impaired originated loans		$	—		$	—		$	21,323		$	21,323
	Other real estate/repossessed assets		—			—			14,205			14,205
	Mortgage servicing rights		—			—			8,691			8,691
	Total		$	—		$	—		$	44,219		$	44,219
	31-Mar-14
	Impaired originated loans		$	—		$	—		$	29,461		$	29,461
	Other real estate/repossessed assets		—			—			10,056			10,056
	Total		$	—		$	—		$	39,517		$	39,517
Summary of carrying amounts and estimated fair values of the financial instruments	A summary of carrying amounts and estimated fair values of the Corporation’s financial instruments included in the consolidated statements of financial position was as follows:
		Level in Fair Value Measurement		31-Mar-15						31-Dec-14					31-Mar-14
		Hierarchy		Carrying			Fair			Carrying			Fair		Carrying		Fair
				Amount			Value			Amount			Value		Amount		Value
				(In thousands)
	Assets:
	Cash and cash equivalents	Level 1		$	393,938		$	393,938		$	183,020		$	183,020	$	382,385	$	382,385
	Investment securities:
	Available-for-sale	Level 1		8,302			8,302			8,259			8,259		—		—
	Available-for-sale	Level 2		672,342			672,342			740,605			740,605		657,818		657,818
	Held-to-maturity	Level 2		370,950			372,876			305,913			308,650		267,599		265,947
	Held-to-maturity	Level 3		10,500			7,300			10,500			7,090		10,500		6,460
	Nonmarketable equity securities	NA		31,249			31,249			27,369			27,369		25,572		25,572
	Loans held-for-sale	Level 2		9,675			9,675			9,128			9,128		3,814		3,814
	Net loans	Level 3		5,627,618			5,633,217			5,612,547			5,623,454		4,674,816		4,688,814
	Interest receivable	Level 2		19,816			19,816			17,492			17,492		16,945		16,945
	Liabilities:
	Deposits without defined maturities	Level 2		$	4,988,268		$	4,988,268		$	4,741,024		$	4,741,024	$	3,868,700	$	3,868,700
	Time deposits	Level 3		1,332,085			1,335,605			1,337,947			1,340,015		1,362,593		1,371,312
	Interest payable	Level 2		779			779			755			755		876		876
	Short-term borrowings	Level 2		372,236			372,236			389,467			389,467		361,231		361,231

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Numerator and denominator of the basic and diluted earnings per common share computations	The following summarizes the numerator and denominator of the basic and diluted earnings per common share computations:
		Three Months Ended March 31,
		2015		2014
		(In thousands, except per share data)
	Numerator for both basic and diluted earnings per common share, net income	$	17,835	$	13,813
	Denominator for basic earnings per common share, weighted average common shares outstanding	32,809		29,825
	Weighted average common stock equivalents	235		212
	Denominator for diluted earnings per common share	33,044		30,037
	Basic earnings per common share	$	0.54	$	0.46
	Diluted earnings per common share	0.54		0.46

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of activity for Corporation's stock options	A summary of activity for the Corporation’s stock options as of and for the three months ended March 31, 2015 is presented below:
			Non-Vested						Stock Options Outstanding
			Stock Options Outstanding
			Number of		Weighted-		Weighted-		Number of		Weighted-
			Options		Average		Average		Options		Average
					Exercise		Grant Date				Exercise
					Price		Fair Value Per Share				Price
					Per Share						Per Share
	Outstanding at December 31, 2014		432,199		$	26.75	$	8.3	1,037,311		$	25.9
	Granted		244,165		30.18		8.4		244,165		30.18
	Exercised		—		—		—		(37,191	)	23.11
	Vested		(150,224	)	25.57		7.8		—		—
	Forfeited/expired		(3,049	)	27.42		8.59		(3,049	)	27.42
	Outstanding at March 31, 2015		523,091		$	28.69	$	8.49	1,241,236		$	26.82
	Exercisable/vested at March 31, 2015								718,145		$	25.46
Assumptions of Black-Scholes option pricing model	The fair value of the stock options granted during the three months ended March 31, 2015 was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions.
	Expected dividend yield	3.5		%
	Risk-free interest rate	1.78		%
	Expected stock price volatility	39.1		%
	Expected life of options – in years	7
	Weighted average fair value of options granted	$	8.4
Summary of activity for restricted stock performance units	A summary of the activity for restricted stock units as of and for the three months ended March 31, 2015 is presented below:
			Number of		Weighted-
			Units		Average
					Grant Date
					Fair Value
					Per Unit
	Outstanding at December 31, 2014		204,319		$	24.14
	Granted		76,286		28.15
	Converted into shares of common stock		(66,769	)	22.32
	Forfeited/expired		(405	)	25.17
	Outstanding at March 31, 2015		213,431		$	26.14

Pension_and_Other_Postretireme1

Pension and Other Postretirement Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan	The components of net periodic benefit cost for the Corporation’s qualified and nonqualified pension plans and nonqualified postretirement benefit plan are as follows:
		Three Months Ended March 31,
		2015			2014
		(In thousands)
	Defined Benefit Pension Plans
	Service cost	$	273		$	250
	Interest cost	1,332			1,312
	Expected return on plan assets	(2,161		)	(2,078		)
	Amortization of prior service credit	(1		)	—
	Amortization of unrecognized net loss	1,056			569
	Net periodic benefit cost	$	499		$	53
	Postretirement Benefit Plan
	Service cost	$	4		$	5
	Interest cost	33			35
	Amortization of prior service cost	32			32
	Amortization of unrecognized net gain	—			(26		)
	Net periodic benefit cost	$	69		$	46

Significant_Accounting_Policie2

Significant Accounting Policies (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Jun. 24, 2014	Sep. 18, 2013	Apr. 20, 2009	Jan. 31, 2008	Apr. 20, 2015
	Bank
Business Acquisition [Line Items]
Number of banks through which company operates	1
Number of regional banking units Chemical Bank operates through	4
Number of minimum days when principal or interest is past due is placed in nonaccrual category	90 days
Number of minimum days in real estate residential loan when principal or interest is past due is placed in nonaccrual category	120 days
Time period in which payments receive consistently and loans are returned to accrual status	6 months
Time period sustained for payment history of principal and interest payments to move them to performing status	6 months
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
Minimum number of days past due as to interest or principal payments in accruing loans moves to nonperforming loans	90 days
Minimum amount of loan reviewed for detailed credit quality	$250,000
Time period for historical loan loss experience	5 years
Minimum percentage of tax benefit is recognized for the amount likely to be realized	50.00%
Reserve for contingent income tax liabilities recorded	0	0	0
Expense related to qualified affordable housing projects	100,000	100,000
Remaining investment in qualified affordable housing projects	4,800,000	3,200,000	4,900,000
Number of shares authorized to be repurchased							500,000
Stock repurchased (shares)	0
Number of remaining shares authorized to be repurchased (shares)	500,000
Common Stock, Shares, Issued	32,847,063	29,865,841	32,774,420	2,500,000	2,213,750
CommonStockIssuedOverAllotment				375,000	288,750
Gross Value of Common Stock sold in public stock offering				80,500,000
Shares Issued, Price Per Share				$28	$26
Issuance of common stock, net of issuance costs				$76,200,000	$53,900,000
Preferred stock, shares authorized	200,000	200,000	200,000			200,000
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0
Common Stock, Shares Authorized	45,000,000	45,000,000	45,000,000
Northwestern Bancorp [Member]
Business Acquisition [Line Items]
Number of pools of aggregate acquired loans based upon common risk characteristics	4
OAK [Member]
Business Acquisition [Line Items]
Number of pools of aggregate acquired loans based upon common risk characteristics	14
Shareholder Approved Proposal [Member]
Business Acquisition [Line Items]
Preferred stock, shares authorized								2,000,000
Common Stock, Shares Authorized								60,000,000

Acquisitions_Activity_for_Acqu

Acquisitions (Activity for Acquired Loans) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period	$137,961
Accretable Yield Additions, Net of Reductions	-696	[1]
Accretion recognized in interest income	-8,205
Reclassification from nonaccretable difference	0
Balance at end of period	129,060
Northwestern Bancorp [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period	104,675
Accretable Yield Additions, Net of Reductions	-1,410	[1]
Accretion recognized in interest income	-4,998
Reclassification from nonaccretable difference	0
Balance at end of period	98,267
OAK [Member]
Activity for accretable yield includes contractually due interest of acquired loans
Balance at beginning of period	33,286		32,610
Accretable Yield Additions, Net of Reductions	714	[1]	821	[1]
Accretion recognized in interest income	-3,207		-3,843
Reclassification from nonaccretable difference	0		10,000
Balance at end of period	$30,793		$39,588
[1]	Represents additions of estimated contractual interest expected to be collected from acquired loans being renewed or extended, less reductions in contractual interest resulting from the early payoff of acquired loans.

Acquisitions_Textual_Details

Acquisitions (Textual) (Details) (USD $)	0 Months Ended
	Jan. 05, 2015	Apr. 01, 2015	Oct. 31, 2014	Dec. 07, 2012	Apr. 30, 2010	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
				Branches	Offices
Business Acquisition [Line Items]
Goodwill						$180,128,000	$180,128,000	$120,164,000
Lake Michigan Financial Corp [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price	$16.64
Exchange Ratio of Common Stock Issued, Business Combinations	1.326
Acquisition purchase price	184,100,000
Monarch Community Bancorp [Member]
Business Acquisition [Line Items]
Exchange Ratio of Common Stock Issued, Business Combinations		0.0982
Business Combination, Acquired Receivables, Fair Value						128,000,000
Acquisition purchase price		27,200,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares		861,000
Assets of acquiree company						170,000,000
Deposits of acquiree company						143,000,000
Northwestern Bancorp [Member]
Business Acquisition [Line Items]
Expected Principal Cash Flows of Contractually Required Acquired Loan Portfolio			481,000,000
Expected Interest Cash Flows of Contractually Required Acquired Loan Portfolio			104,000,000
Business Combination, Acquired Receivables, Fair Value			475,000,000
Certain Loans Acquired in Transfer, Nonaccretable Difference			34,000,000
Acquisition purchase price			121,000,000
Goodwill			60,000,000
Intangibles acquired			12,900,000
Service provided by acquiree bank through number of branches			25
Assets of acquiree company			815,000,000
Deposits of acquiree company			794,000,000
Outstanding contractual principal balance of acquired loan portfolio						453,000,000	485,000,000
Carrying amount of acquired loan portfolio						421,000,000	452,000,000
Business Combination, Acquired Receivables, Gross Contractual Amount			507,000,000
Interest Payments Receivable of Acquired Loan Portfolio			112,000,000
Business Combination, Acquired Receivables, Estimated Uncollectible			26,000,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Disposals of Loans			110,000,000
Independent Bank [Member]
Business Acquisition [Line Items]
Number of branches acquired (branches)				21
Deposits acquired				404,000,000
Loans acquired				44,000,000
Acquisition purchase price				8,100,000
Premium paid on deposits purchased				11,500,000
Premium paid as a percentage of deposits purchased (percent)				2.85%
Discount on loans purchased (percent)				1.75%
Goodwill				6,800,000
Independent Bank [Member] | Core Deposits [Member]
Business Acquisition [Line Items]
Intangibles acquired				5,600,000
OAK [Member]
Business Acquisition [Line Items]
Loans acquired					627,000,000
Acquisition purchase price					83,700,000
Service provided by acquiree bank through number of branches					14
Assets of acquiree company					820,000,000
Deposits of acquiree company					693,000,000
Brokered deposits of acquiree company					193,000,000
Contractually required principal payments of loan portfolio, acquisition date					683,000,000
Acquired loan portfolio acquisition date fair value					627,000,000
Outstanding contractual principal balance of acquired loan portfolio						255,000,000	268,000,000	313,000,000
Carrying amount of acquired loan portfolio						$234,000,000	$246,000,000	$289,000,000

Investment_Securities_Summary_

Investment Securities (Summary of Amortized Cost and Fair Value of Available-For-Sale Investment Securities) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	$677,940	$749,187	$659,183
Investment securities available-for-sale, Unrealized Gains	3,646	3,003	3,794
Investment securities available-for-sale, Unrealized Losses	942	3,326	5,159
Available-for-sale Securities, Total	680,644	748,864	657,818
US Treasury Securities [Member]
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	8,271	8,272
Investment securities available-for-sale, Unrealized Gains	31	0
Investment securities available-for-sale, Unrealized Losses	0	13
Available-for-sale Securities, Total	8,302	8,259
Government sponsored agencies [Member]
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	249,642	263,658	91,613
Investment securities available-for-sale, Unrealized Gains	889	356	295
Investment securities available-for-sale, Unrealized Losses	101	511	298
Available-for-sale Securities, Total	250,430	263,503	91,610
State and political subdivisions [Member]
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	31,701	45,157	42,369
Investment securities available-for-sale, Unrealized Gains	624	1,087	1,408
Investment securities available-for-sale, Unrealized Losses	3	17	0
Available-for-sale Securities, Total	32,322	46,227	43,777
Residential mortgage-backed securities [Member]
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	218,299	240,465	291,187
Investment securities available-for-sale, Unrealized Gains	1,358	885	1,023
Investment securities available-for-sale, Unrealized Losses	56	1,543	3,472
Available-for-sale Securities, Total	219,601	239,807	288,738
Collateralized Mortgage Obligations [Member]
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	133,713	145,316	167,622
Investment securities available-for-sale, Unrealized Gains	305	261	393
Investment securities available-for-sale, Unrealized Losses	718	1,194	1,296
Available-for-sale Securities, Total	133,300	144,383	166,719
Corporate bonds [Member]
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	34,925	44,930	65,003
Investment securities available-for-sale, Unrealized Gains	136	213	505
Investment securities available-for-sale, Unrealized Losses	64	48	93
Available-for-sale Securities, Total	34,997	45,095	65,415
Preferred stock [Member]
Available-for-sale Securities
Investment securities available-for-sale, Amortized Cost	1,389	1,389	1,389
Investment securities available-for-sale, Unrealized Gains	303	201	170
Investment securities available-for-sale, Unrealized Losses	0	0	0
Available-for-sale Securities, Total	$1,692	$1,590	$1,559

Investment_Securities_Summary_1

Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$381,450	$316,413	$278,099
Investment securities held-to-maturity, Unrealized Gains	6,852	7,294	5,331
Investment securities held-to-maturity, Unrealized Losses	8,126	7,967	11,023
Total Held-to-maturity securities, Debt maturities, Fair Value	380,176	315,740	272,407
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	370,950	305,913	267,599
Investment securities held-to-maturity, Unrealized Gains	6,852	7,294	5,331
Investment securities held-to-maturity, Unrealized Losses	4,926	4,557	6,983
Total Held-to-maturity securities, Debt maturities, Fair Value	372,876	308,650	265,947
Trust Preferred Securities [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	10,500	10,500	10,500
Investment securities held-to-maturity, Unrealized Gains	0	0	0
Investment securities held-to-maturity, Unrealized Losses	3,200	3,410	4,040
Total Held-to-maturity securities, Debt maturities, Fair Value	$7,300	$7,090	$6,460

Investment_Securities_Maturiti

Investment Securities (Maturities of Debt Securities) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$180,558
Due after one year through five years, Amortized Cost	442,088
Due after five years through ten years, Amortized Cost	50,902
Due after ten years, Amortized Cost	3,003
Preferred stock, Amortized Cost	1,389
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	677,940
Due in one year or less , Fair Value	180,869
Due after one year through five years, Fair Value	443,752
Due after five years through ten years, Fair Value	51,302
Due after ten years, Fair Value	3,029
Preferred stock, Fair Value	1,692
Total Available-for-sale securities, Debt maturities, Fair Value	680,644
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	35,293
Due after one year through five years, Amortized Cost	171,557
Due after five years through ten years, Amortized Cost	120,799
Due after ten years, Amortized Cost	53,801
Total Held-to-maturity securities, Debt maturities, Amortized Cost	381,450	316,413	278,099
Due in one year or less , Fair Value	35,365
Due after one year through five years, Fair Value	172,699
Due after five years through ten years, Fair Value	122,512
Due after ten years, Fair Value	49,600
Total Held-to-maturity securities, Debt maturities, Fair Value	$380,176	$315,740	$272,407

Investment_Securities_Summary_2

Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$293,885	$317,885	$449,480
Less Than 12 Months, Gross Unrealized Losses	2,114	3,998	9,409
12 Months or More, Fair Value	135,889	302,630	105,584
12 Months or More, Gross Unrealized Losses	6,954	7,295	6,773
Total, Fair Value	429,774	620,515	555,064
Total, Gross Unrealized Losses	9,068	11,293	16,182
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	27,889	166,963	45,396
Less Than 12 Months, Gross Unrealized Losses	64	406	110
12 Months or More, Fair Value	18,896	31,927	15,204
12 Months or More, Gross Unrealized Losses	37	105	188
Total, Fair Value	46,785	198,890	60,600
Total, Gross Unrealized Losses	101	511	298
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	156,010	62,310	79,787
Less Than 12 Months, Gross Unrealized Losses	1,989	3,348	4,942
12 Months or More, Fair Value	49,839	36,847	56,180
12 Months or More, Gross Unrealized Losses	2,940	1,226	2,041
Total, Fair Value	205,849	99,157	135,967
Total, Gross Unrealized Losses	4,929	4,574	6,983
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	82,303	17,276	247,397
Less Than 12 Months, Gross Unrealized Losses	28	52	3,472
12 Months or More, Fair Value	3,847	180,194	0
12 Months or More, Gross Unrealized Losses	28	1,491	0
Total, Fair Value	86,150	197,470	247,397
Total, Gross Unrealized Losses	56	1,543	3,472
Collateralized Mortgage Obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	22,694	63,077	76,900
Less Than 12 Months, Gross Unrealized Losses	22	179	885
12 Months or More, Fair Value	41,061	31,620	12,833
12 Months or More, Gross Unrealized Losses	696	1,015	411
Total, Fair Value	63,755	94,697	89,733
Total, Gross Unrealized Losses	718	1,194	1,296
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	4,989	0	0
Less Than 12 Months, Gross Unrealized Losses	11	0	0
12 Months or More, Fair Value	14,946	14,952	14,907
12 Months or More, Gross Unrealized Losses	53	48	93
Total, Fair Value	19,935	14,952	14,907
Total, Gross Unrealized Losses	64	48	93
Trust Preferred Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	0	0
Less Than 12 Months, Gross Unrealized Losses	0	0	0
12 Months or More, Fair Value	7,300	7,090	6,460
12 Months or More, Gross Unrealized Losses	3,200	3,410	4,040
Total, Fair Value	7,300	7,090	6,460
Total, Gross Unrealized Losses	3,200	3,410	4,040
US Treasury Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	8,259
Less Than 12 Months, Gross Unrealized Losses	0	13
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	0	8,259
Total, Gross Unrealized Losses	$0	$13

Investment_Securities_Textual_

Investment Securities (Textual) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Trust preferred investment securities held to maturity	$10.50
Trust preferred investment security of Non Public bank company	10
Interest in Trust preferred investment security	100.00%
Remaining trust preferred investment security of Non Public bank company	0.5
Interest in another trust preferred investment security	10.00%
Carrying value of trust preferred investment security one	10
Carrying value of trust preferred investment security two	0.5
Fair value of trust preferred investment security one	7
Fair value of trust preferred investment security two	0.3
Unrealized loss on trust preferred investment securities	3.2
Unrealized loss on trust preferred securities.	$3.20

Loans_Summary_of_Loans_Details

Loans (Summary of Loans) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Summary of loans under portfolio
Commercial loan	$3,081,931	$3,084,024	$2,586,653
Consumer loan	2,620,943	2,604,206	2,166,636
Total loans	5,702,874	5,688,230	4,753,289
Commercial [Member]
Summary of loans under portfolio
Commercial loan	1,356,169	1,354,881	1,208,641
Real estate commercial [Member]
Summary of loans under portfolio
Commercial loan	1,616,923	1,557,648	1,279,167
Real estate construction [Member]
Summary of loans under portfolio
Commercial loan	95,923	152,745	85,084
Land development [Member]
Summary of loans under portfolio
Commercial loan	12,916	18,750	13,761
Real estate residential [Member]
Summary of loans under portfolio
Consumer loan	1,117,445	1,110,390	962,009
Consumer installment [Member]
Summary of loans under portfolio
Consumer loan	844,066	829,570	675,412
Home equity [Member]
Summary of loans under portfolio
Consumer loan	$659,432	$664,246	$529,215

Loans_Summary_of_Recorded_Inve

Loans (Summary of Recorded Investment of Commercial Loans by Risk Rating Categories) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	$3,081,931	$3,084,024	$2,586,653
Commercial [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,356,169	1,354,881	1,208,641
Real estate commercial [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,616,923	1,557,648	1,279,167
Real estate construction [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	95,923	152,745	85,084
Land development [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	12,916	18,750	13,761
Originated Portfolio [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	2,637,440	2,603,592	2,340,010
Originated Portfolio [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	2,447,891	2,423,966	2,169,841
Originated Portfolio [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	85,985	74,942	53,969
Originated Portfolio [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	58,941	62,913	67,954
Originated Portfolio [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	44,617	41,762	47,280
Originated Portfolio [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	6	9	966
Originated Portfolio [Member] | Commercial [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,264,907	1,255,898	1,131,121
Originated Portfolio [Member] | Commercial [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,176,021	1,171,817	1,060,743
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	40,999	37,800	18,359
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	28,983	29,863	33,768
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	18,904	16,417	17,301
Originated Portfolio [Member] | Commercial [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	1	950
Originated Portfolio [Member] | Real estate commercial [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,272,348	1,204,426	1,128,718
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,175,373	1,114,529	1,034,517
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	44,248	34,996	33,962
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	27,961	29,935	32,671
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	24,760	24,958	27,552
Originated Portfolio [Member] | Real estate commercial [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	6	8	16
Originated Portfolio [Member] | Real estate construction [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	95,923	138,740	72,405
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	93,864	134,668	70,750
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	1,408	680
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,396	2,502	815
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	663	162	160
Originated Portfolio [Member] | Real estate construction [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Originated Portfolio [Member] | Land development [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	4,262	4,528	7,766
Originated Portfolio [Member] | Land development [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	2,633	2,952	3,831
Originated Portfolio [Member] | Land development [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	738	738	968
Originated Portfolio [Member] | Land development [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	601	613	700
Originated Portfolio [Member] | Land development [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	290	225	2,267
Originated Portfolio [Member] | Land development [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	444,491	480,432	246,643
Acquired Portfolio [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	396,259	423,592	223,041
Acquired Portfolio [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	19,338	21,968	5,050
Acquired Portfolio [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	19,384	16,764	11,388
Acquired Portfolio [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	9,510	18,108	7,164
Acquired Portfolio [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Commercial [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	91,262	98,983	77,520
Acquired Portfolio [Member] | Commercial [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	71,422	76,780	67,326
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	11,299	12,687	2,423
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	6,509	4,089	3,635
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	2,032	5,427	4,136
Acquired Portfolio [Member] | Commercial [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate commercial [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	344,575	353,222	150,449
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	318,113	321,018	139,130
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	7,786	8,698	2,627
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	12,735	12,478	7,753
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	5,941	11,028	939
Acquired Portfolio [Member] | Real estate commercial [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	14,005	12,679
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	14,005	12,679
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Real estate construction [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	0	0	0
Acquired Portfolio [Member] | Land development [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	8,654	14,222	5,995
Acquired Portfolio [Member] | Land development [Member] | Risk Grades 1-5 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	6,724	11,789	3,906
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 6 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	253	583	0
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 7 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	140	197	0
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 8 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	1,537	1,653	2,089
Acquired Portfolio [Member] | Land development [Member] | Risk Grade 9 [Member]
Recorded investment of loans in commercial loan portfolio by risk rating categories
Recorded investment (loan balance), Commercial, Total	$0	$0	$0

Loans_Summary_of_Recorded_Inve1

Loans (Summary of Recorded Investment of Consumer Loans by Risk Rating Categories) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	$2,620,943	$2,604,206	$2,166,636
Real estate residential [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	1,117,445	1,110,390	962,009
Consumer installment [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	844,066	829,570	675,412
Home equity [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	659,432	664,246	529,215
Originated Loans [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	2,411,222	2,386,475	2,124,455
Originated Loans [Member] | Real estate residential [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	1,007,572	998,001	950,801
Originated Loans [Member] | Consumer installment [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	835,359	819,378	673,790
Originated Loans [Member] | Home equity [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	568,291	569,096	499,864
Originated Loans [Member] | Performing [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	2,399,114	2,372,503	2,108,148
Originated Loans [Member] | Performing [Member] | Real estate residential [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	998,196	987,542	937,968
Originated Loans [Member] | Performing [Member] | Consumer installment [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	834,926	818,878	672,984
Originated Loans [Member] | Performing [Member] | Home equity [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	565,992	566,083	497,196
Originated Loans [Member] | Nonperforming [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	12,108	13,972	16,307
Originated Loans [Member] | Nonperforming [Member] | Real estate residential [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	9,376	10,459	12,833
Originated Loans [Member] | Nonperforming [Member] | Consumer installment [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	433	500	806
Originated Loans [Member] | Nonperforming [Member] | Home equity [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	2,299	3,013	2,668
Acquired Loans [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	209,721	217,731	42,181
Acquired Loans [Member] | Real estate residential [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	109,873	112,389	11,208
Acquired Loans [Member] | Consumer installment [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	8,707	10,192	1,622
Acquired Loans [Member] | Home equity [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	91,141	95,150	29,351
Acquired Loans [Member] | Performing [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	208,387	215,971	41,792
Acquired Loans [Member] | Performing [Member] | Real estate residential [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	109,005	111,101	11,150
Acquired Loans [Member] | Performing [Member] | Consumer installment [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	8,696	10,174	1,622
Acquired Loans [Member] | Performing [Member] | Home equity [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	90,686	94,696	29,020
Acquired Loans [Member] | Nonperforming [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	1,334	1,760	389
Acquired Loans [Member] | Nonperforming [Member] | Real estate residential [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	868	1,288	58
Acquired Loans [Member] | Nonperforming [Member] | Consumer installment [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	11	18	0
Acquired Loans [Member] | Nonperforming [Member] | Home equity [Member]
Recorded investment of loans in consumer loan portfolio based on credit risk profile of loans in performing and nonperforming status
Recorded investment (loan balance), Consumer, Total	$455	$454	$331

Loans_Summary_of_Nonperforming

Loans (Summary of Nonperforming Loans) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Summary of nonperforming loans
Total TDRs	$101,824	$101,322	$103,671
Total loans	5,702,874	5,688,230	4,753,289
Minimum number of days accruing loans past due move to nonaccrual status	90 days
Commercial Loan Portfolio [Member]
Summary of nonperforming loans
Total TDRs	77,511	77,047	79,852
Total loans	3,081,931	3,084,024	2,586,653
Consumer Loan Portfolio [Member]
Summary of nonperforming loans
Total TDRs	24,313	24,275	23,819
Total loans	2,620,943	2,604,206	2,166,636
Nonperforming [Member]
Summary of nonperforming loans
Total nonaccrual loans	53,440	50,644	57,687
Total accruing loans contractually past due 90 days or more as to interest or principal payments	801	2,073	1,395
Total TDRs	18,500	18,467	17,462
Total loans	72,741	71,184	76,544
Nonperforming [Member] | Commercial Loan Portfolio [Member]
Summary of nonperforming loans
Total TDRs	15,810	15,271	11,218
Nonperforming [Member] | Consumer Loan Portfolio [Member]
Summary of nonperforming loans
Total TDRs	2,690	3,196	6,244
Nonperforming [Member] | Commercial [Member]
Summary of nonperforming loans
Total nonaccrual loans	18,904	16,418	18,251
Total accruing loans contractually past due 90 days or more as to interest or principal payments	52	170	43
Nonperforming [Member] | Real estate commercial [Member]
Summary of nonperforming loans
Total nonaccrual loans	24,766	24,966	27,568
Total accruing loans contractually past due 90 days or more as to interest or principal payments	148	0	730
Nonperforming [Member] | Real Estate Construction Loans [Member]
Summary of nonperforming loans
Total nonaccrual loans	663	162	160
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Land Development Loans [Member]
Summary of nonperforming loans
Total nonaccrual loans	290	225	2,267
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Real estate residential [Member]
Summary of nonperforming loans
Total nonaccrual loans	6,514	6,706	6,589
Total accruing loans contractually past due 90 days or more as to interest or principal payments	172	557	0
Nonperforming [Member] | Consumer Installment Loans [Member]
Summary of nonperforming loans
Total nonaccrual loans	433	500	806
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	0	0
Nonperforming [Member] | Home Equity Loans [Member]
Summary of nonperforming loans
Total nonaccrual loans	1,870	1,667	2,046
Total accruing loans contractually past due 90 days or more as to interest or principal payments	$429	$1,346	$622

Loans_Summary_of_Impaired_Loan

Loans (Summary of Impaired Loans by Classes of Loans) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Impaired loans with a valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	$25,100	$23,234	$27,198
Unpaid Principal Balance	25,375	23,648	27,526
Related Valuation Allowance	1,912	1,338	2,065
Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	104,052	111,433	101,297
Unpaid Principal Balance	133,493	141,622	122,701
Related Valuation Allowance	0	0	0
Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	129,152	134,667	128,495
Unpaid Principal Balance	158,868	165,270	150,227
Related Valuation Allowance	1,912	1,338	2,065
Commercial [Member] | Impaired loans with a valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	3,433	966	3,534
Unpaid Principal Balance	3,527	1,040	3,704
Related Valuation Allowance	1,119	293	1,250
Commercial [Member] | Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	33,733	38,094	38,150
Unpaid Principal Balance	39,382	44,557	42,914
Related Valuation Allowance	0	0	0
Commercial [Member] | Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	37,166	39,060	41,684
Unpaid Principal Balance	42,909	45,597	46,618
Related Valuation Allowance	1,119	293	1,250
Real estate commercial [Member] | Impaired loans with a valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	1,780	2,587	3,720
Unpaid Principal Balance	1,961	2,927	3,878
Related Valuation Allowance	496	710	371
Real estate commercial [Member] | Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	57,628	60,616	49,074
Unpaid Principal Balance	79,696	82,693	62,207
Related Valuation Allowance	0	0	0
Real estate commercial [Member] | Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	59,408	63,203	52,794
Unpaid Principal Balance	81,657	85,620	66,085
Related Valuation Allowance	496	710	371
Real estate construction [Member] | Impaired loans with a valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	0	0	0
Unpaid Principal Balance	0	0	0
Related Valuation Allowance	0	0	0
Real estate construction [Member] | Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	663	162	160
Unpaid Principal Balance	836	255	366
Related Valuation Allowance	0	0	0
Real estate construction [Member] | Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	663	162	160
Unpaid Principal Balance	836	255	366
Related Valuation Allowance	0	0	0
Land development [Member] | Impaired loans with a valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	0	0	0
Unpaid Principal Balance	0	0	0
Related Valuation Allowance	0	0	0
Land development [Member] | Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	1,877	1,928	4,472
Unpaid Principal Balance	3,428	3,484	7,773
Related Valuation Allowance	0	0	0
Land development [Member] | Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	1,877	1,928	4,472
Unpaid Principal Balance	3,428	3,484	7,773
Related Valuation Allowance	0	0	0
Real estate residential [Member] | Impaired loans with a valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	19,887	19,681	19,944
Unpaid Principal Balance	19,887	19,681	19,944
Related Valuation Allowance	297	335	444
Real estate residential [Member] | Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	7,382	7,994	6,589
Unpaid Principal Balance	7,382	7,994	6,589
Related Valuation Allowance	0	0	0
Real estate residential [Member] | Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	27,269	27,675	26,533
Unpaid Principal Balance	27,269	27,675	26,533
Related Valuation Allowance	297	335	444
Consumer installment [Member] | Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	444	518	806
Unpaid Principal Balance	444	518	806
Related Valuation Allowance	0	0	0
Consumer installment [Member] | Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	444	518	806
Unpaid Principal Balance	444	518	806
Related Valuation Allowance	0	0	0
Home equity [Member] | Impaired loans with no valuation allowance [Member]
Schedule of Impaired loans by classes
Recorded Investment	2,325	2,121	2,046
Unpaid Principal Balance	2,325	2,121	2,046
Related Valuation Allowance	0	0	0
Home equity [Member] | Total Impaired Loans [Member]
Schedule of Impaired loans by classes
Recorded Investment	2,325	2,121	2,046
Unpaid Principal Balance	2,325	2,121	2,046
Related Valuation Allowance	$0	$0	$0

Loans_Summary_of_Information_R

Loans (Summary of Information Related to Impaired Loans) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	$131,534	$129,459
Interest income recognized related to loans with impaired status	1,180	1,034
Commercial [Member]
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	38,576	41,607
Interest income recognized related to loans with impaired status	289	333
Real estate commercial [Member]
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	60,240	53,320
Interest income recognized related to loans with impaired status	525	361
Real estate construction [Member]
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	640	167
Interest income recognized related to loans with impaired status	0	0
Land development [Member]
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	1,875	4,643
Interest income recognized related to loans with impaired status	27	37
Real estate residential [Member]
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	27,352	26,781
Interest income recognized related to loans with impaired status	331	303
Consumer installment [Member]
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	499	773
Interest income recognized related to loans with impaired status	0	0
Home equity [Member]
Schedule representing information related to impaired loans
Average recorded investment related to impaired loans	2,352	2,168
Interest income recognized related to loans with impaired status	$8	$0

Loans_Summary_of_the_Aging_Sta

Loans (Summary of the Aging Status of the Recorded Investment in Loans by Portfolio Segment/Class) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Originated Portfolio [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	$22,816	$20,595	$14,824
Financing receivable, recorded investment 61 to 89 days past due	3,625	3,352	4,637
Financing receivable, recorded investment accruing loans past due 90 days or more	801	2,073	1,395
Financing receivable, recorded investment, Nonaccrual loans	53,440	50,644	57,687
Financing receivable recorded investment, Total past due	80,682	76,664	78,543
Financing receivable, recorded investment, current	4,967,980	4,913,403	4,385,922
Financing receivable, recorded investment, Total loans	5,048,662	4,990,067	4,464,465
Originated Portfolio [Member] | Commercial [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	10,121	4,033	6,003
Financing receivable, recorded investment 61 to 89 days past due	729	743	1,832
Financing receivable, recorded investment accruing loans past due 90 days or more	52	170	43
Financing receivable, recorded investment, Nonaccrual loans	18,904	16,418	18,251
Financing receivable recorded investment, Total past due	29,806	21,364	26,129
Financing receivable, recorded investment, current	1,235,101	1,234,534	1,104,992
Financing receivable, recorded investment, Total loans	1,264,907	1,255,898	1,131,121
Originated Portfolio [Member] | Real estate commercial [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	7,238	7,515	4,094
Financing receivable, recorded investment 61 to 89 days past due	2,267	1,383	1,098
Financing receivable, recorded investment accruing loans past due 90 days or more	148	0	730
Financing receivable, recorded investment, Nonaccrual loans	24,766	24,966	27,568
Financing receivable recorded investment, Total past due	34,419	33,864	33,490
Financing receivable, recorded investment, current	1,237,929	1,170,562	1,095,228
Financing receivable, recorded investment, Total loans	1,272,348	1,204,426	1,128,718
Originated Portfolio [Member] | Real estate construction [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	340	262	18
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	663	162	160
Financing receivable recorded investment, Total past due	1,003	424	178
Financing receivable, recorded investment, current	94,920	138,316	72,227
Financing receivable, recorded investment, Total loans	95,923	138,740	72,405
Originated Portfolio [Member] | Land development [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	0	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	290	225	2,267
Financing receivable recorded investment, Total past due	290	225	2,267
Financing receivable, recorded investment, current	3,972	4,303	5,499
Financing receivable, recorded investment, Total loans	4,262	4,528	7,766
Originated Portfolio [Member] | Real estate residential [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	1,246	2,126	1,259
Financing receivable, recorded investment 61 to 89 days past due	88	54	1,138
Financing receivable, recorded investment accruing loans past due 90 days or more	172	557	0
Financing receivable, recorded investment, Nonaccrual loans	6,514	6,706	6,589
Financing receivable recorded investment, Total past due	8,020	9,443	8,986
Financing receivable, recorded investment, current	999,552	988,558	941,815
Financing receivable, recorded investment, Total loans	1,007,572	998,001	950,801
Originated Portfolio [Member] | Consumer installment [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	2,143	3,620	1,950
Financing receivable, recorded investment 61 to 89 days past due	344	512	313
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	433	500	806
Financing receivable recorded investment, Total past due	2,920	4,632	3,069
Financing receivable, recorded investment, current	832,439	814,746	670,721
Financing receivable, recorded investment, Total loans	835,359	819,378	673,790
Originated Portfolio [Member] | Home equity [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	1,728	3,039	1,500
Financing receivable, recorded investment 61 to 89 days past due	197	660	256
Financing receivable, recorded investment accruing loans past due 90 days or more	429	1,346	622
Financing receivable, recorded investment, Nonaccrual loans	1,870	1,667	2,046
Financing receivable recorded investment, Total past due	4,224	6,712	4,424
Financing receivable, recorded investment, current	564,067	562,384	495,440
Financing receivable, recorded investment, Total loans	568,291	569,096	499,864
Acquired Portfolio [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	2,299	2,994	98
Financing receivable, recorded investment 61 to 89 days past due	378	461	0
Financing receivable, recorded investment accruing loans past due 90 days or more	11,231	19,892	11,523
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	13,908	23,347	11,621
Financing receivable, recorded investment, current	640,304	674,816	277,203
Financing receivable, recorded investment, Total loans	654,212	698,163	288,824
Acquired Portfolio [Member] | Commercial [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	59	133	0
Financing receivable, recorded investment 61 to 89 days past due	5	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	2,089	5,427	6,496
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	2,153	5,560	6,496
Financing receivable, recorded investment, current	89,109	93,423	71,024
Financing receivable, recorded investment, Total loans	91,262	98,983	77,520
Acquired Portfolio [Member] | Real estate commercial [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	1,784	2,014	0
Financing receivable, recorded investment 61 to 89 days past due	138	352	0
Financing receivable, recorded investment accruing loans past due 90 days or more	6,271	11,052	2,549
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	8,193	13,418	2,549
Financing receivable, recorded investment, current	336,382	339,804	147,900
Financing receivable, recorded investment, Total loans	344,575	353,222	150,449
Acquired Portfolio [Member] | Real estate construction [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	0	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	0	0	0
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	0	0	0
Financing receivable, recorded investment, current	0	14,005	12,679
Financing receivable, recorded investment, Total loans	0	14,005	12,679
Acquired Portfolio [Member] | Land development [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	0	0	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	1,537	1,653	2,089
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	1,537	1,653	2,089
Financing receivable, recorded investment, current	7,117	12,569	3,906
Financing receivable, recorded investment, Total loans	8,654	14,222	5,995
Acquired Portfolio [Member] | Real estate residential [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	104	156	0
Financing receivable, recorded investment 61 to 89 days past due	0	0	0
Financing receivable, recorded investment accruing loans past due 90 days or more	868	18	58
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	972	174	58
Financing receivable, recorded investment, current	108,901	112,215	11,150
Financing receivable, recorded investment, Total loans	109,873	112,389	11,208
Acquired Portfolio [Member] | Consumer installment [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	3	55	49
Financing receivable, recorded investment 61 to 89 days past due	1	3	0
Financing receivable, recorded investment accruing loans past due 90 days or more	11	454	0
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	15	512	49
Financing receivable, recorded investment, current	8,692	9,680	1,573
Financing receivable, recorded investment, Total loans	8,707	10,192	1,622
Acquired Portfolio [Member] | Home equity [Member]
Schedule representing the aging status of the recorded investment in loans by classes
Financing receivable, recorded investment 31 to 60 days past due	349	636	49
Financing receivable, recorded investment 61 to 89 days past due	234	106	0
Financing receivable, recorded investment accruing loans past due 90 days or more	455	1,288	331
Financing receivable, recorded investment, Nonaccrual loans	0	0	0
Financing receivable recorded investment, Total past due	1,038	2,030	380
Financing receivable, recorded investment, current	90,103	93,120	28,971
Financing receivable, recorded investment, Total loans	$91,141	$95,150	$29,351

Loans_Summary_of_TDRs_Details

Loans (Summary of TDRs) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Schedule of corporation's TDRs
Total TDRs	$101,824	$101,322	$103,671
Commercial Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	77,511	77,047	79,852
Consumer Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	24,313	24,275	23,819
Performing [Member]
Schedule of corporation's TDRs
Total TDRs	45,981	45,664	41,823
Performing [Member] | Commercial Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	28,784	29,179	28,123
Performing [Member] | Consumer Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	17,197	16,485	13,700
Nonperforming [Member]
Schedule of corporation's TDRs
Total TDRs	18,500	18,467	17,462
Nonperforming [Member] | Commercial Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	15,810	15,271	11,218
Nonperforming [Member] | Consumer Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	2,690	3,196	6,244
Substandard Nonaccrual [Member]
Schedule of corporation's TDRs
Total TDRs	37,343	37,191	44,386
Substandard Nonaccrual [Member] | Commercial Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	32,917	32,597	40,511
Substandard Nonaccrual [Member] | Consumer Loan Portfolio [Member]
Schedule of corporation's TDRs
Total TDRs	$4,426	$4,594	$3,875

Loans_Summary_of_TDRs_Modified

Loans (Summary of TDRs Modified During the Period) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	Loans	Loans
Schedule providing information on TDRs
Modified TDRs, Number of loans	20	52
Modified TDRs, Pre-modification recorded investment	$4,802	$12,205
Modified TDRs, Post-modification recorded investment	4,802	12,196
Subtotal-commercial loan portfolio [Member] | Commercial Loan Portfolio [Member]
Schedule providing information on TDRs
Modified TDRs, Number of loans	10	22
Modified TDRs, Pre-modification recorded investment	4,466	11,218
Modified TDRs, Post-modification recorded investment	4,466	11,218
Consumer loan portfolio [Member] | Consumer Portfolio Segment [Member]
Schedule providing information on TDRs
Modified TDRs, Number of loans	10	30
Modified TDRs, Pre-modification recorded investment	336	987
Modified TDRs, Post-modification recorded investment	336	978
Commercial [Member] | Commercial Loan Portfolio [Member]
Schedule providing information on TDRs
Modified TDRs, Number of loans	5	12
Modified TDRs, Pre-modification recorded investment	1,932	8,356
Modified TDRs, Post-modification recorded investment	1,932	8,356
Real estate commercial [Member] | Commercial Loan Portfolio [Member]
Schedule providing information on TDRs
Modified TDRs, Number of loans	5	9
Modified TDRs, Pre-modification recorded investment	2,534	2,790
Modified TDRs, Post-modification recorded investment	2,534	2,790
Real Estate Construction Loans [Member] | Commercial Loan Portfolio [Member]
Schedule providing information on TDRs
Modified TDRs, Number of loans		0
Modified TDRs, Pre-modification recorded investment		0
Modified TDRs, Post-modification recorded investment		0
Land development [Member] | Commercial Loan Portfolio [Member]
Schedule providing information on TDRs
Modified TDRs, Number of loans	0	1
Modified TDRs, Pre-modification recorded investment	0	72
Modified TDRs, Post-modification recorded investment	$0	$72

Loans_Summary_of_TDRs_with_a_P

Loans (Summary of TDRs with a Payment Default During the Period) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	Loans	Loans
Troubled debt restructurings on financing receivables with defaults payment
Financing receivable modifications subsequent default number of contract	4	3
Financing receivable modification subsequent default recorded investment	$792	$1,774
Consumer Portfolio Segment [Member]
Troubled debt restructurings on financing receivables with defaults payment
Financing receivable modifications subsequent default number of contract	1	0
Financing receivable modification subsequent default recorded investment	33	0
Commercial [Member] | Commercial Loan Portfolio [Member]
Troubled debt restructurings on financing receivables with defaults payment
Financing receivable modifications subsequent default number of contract	0	1
Financing receivable modification subsequent default recorded investment	0	104
Real estate commercial [Member] | Commercial Loan Portfolio [Member]
Troubled debt restructurings on financing receivables with defaults payment
Financing receivable modifications subsequent default number of contract	3	2
Financing receivable modification subsequent default recorded investment	759	1,670
Real Estate Construction Loans [Member] | Commercial Loan Portfolio [Member]
Troubled debt restructurings on financing receivables with defaults payment
Financing receivable modifications subsequent default number of contract		0
Financing receivable modification subsequent default recorded investment		0
Land Development Loans [Member] | Commercial Loan Portfolio [Member]
Troubled debt restructurings on financing receivables with defaults payment
Financing receivable modifications subsequent default number of contract		0
Financing receivable modification subsequent default recorded investment		0
Subtotal-commercial loan portfolio [Member] | Commercial Loan Portfolio [Member]
Troubled debt restructurings on financing receivables with defaults payment
Financing receivable modifications subsequent default number of contract	3	3
Financing receivable modification subsequent default recorded investment	$759	$1,774

Loans_Schedule_of_the_Allowanc

Loans (Schedule of the Allowance for Loan Losses) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	$75,683	$79,072
Provision for loan losses	1,500	1,600
Charge-offs	-3,143	-3,472
Recoveries	1,216	1,273
Ending balance	75,256	78,473
Allowance for loan losses
Loans individually evaluated for impairment related to allowance for loan losses	1,912	2,065	1,338
Loans collectively evaluated for impairment related to allowance for loan losses	73,344	75,908	73,845
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	500	500
Total	75,256	78,473
Loans individually evaluated for impairment related to recorded investment (loan balance)	109,104	107,531	105,902
Loans collectively evaluated for impairment related to recorded investment (loan balance)	4,939,558	4,356,934	4,884,165
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	654,212	288,824	698,163
Total loans	5,702,874	4,753,289	5,688,230
Commercial Loan Portfolio [Member]
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	44,156	44,482
Provision for loan losses	3,593	960
Charge-offs	-1,504	-1,209
Recoveries	574	777
Ending balance	46,819	45,010
Allowance for loan losses
Loans individually evaluated for impairment related to allowance for loan losses	1,615	1,621	1,003
Loans collectively evaluated for impairment related to allowance for loan losses	45,204	43,389	43,153
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	0	0
Total	46,819	45,010
Loans individually evaluated for impairment related to recorded investment (loan balance)	89,217	87,587	86,221
Loans collectively evaluated for impairment related to recorded investment (loan balance)	2,548,223	2,252,423	2,517,371
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	444,491	246,643	480,432
Total loans	3,081,931	2,586,653	3,084,024
Consumer Loan Portfolio [Member]
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	28,803	30,145
Provision for loan losses	-3,227	855
Charge-offs	-1,639	-2,263
Recoveries	642	496
Ending balance	24,579	29,233
Allowance for loan losses
Loans individually evaluated for impairment related to allowance for loan losses	297	444	335
Loans collectively evaluated for impairment related to allowance for loan losses	24,282	28,289	27,968
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	500	500
Total	24,579	29,233
Loans individually evaluated for impairment related to recorded investment (loan balance)	19,887	19,944	19,681
Loans collectively evaluated for impairment related to recorded investment (loan balance)	2,391,335	2,104,511	2,366,794
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	209,721	42,181	217,731
Total loans	2,620,943	2,166,636	2,604,206
Unallocated [Member]
Schedule of allowance and recorded investment related to financing receivables segregated by portfolio segment
Beginning balance	2,724	4,445
Provision for loan losses	1,134	-215
Charge-offs	0	0
Recoveries	0	0
Ending balance	3,858	4,230
Allowance for loan losses
Loans individually evaluated for impairment related to allowance for loan losses	0	0	0
Loans collectively evaluated for impairment related to allowance for loan losses	3,858	4,230	2,724
Loans acquired with deteriorated credit quality related to allowance for loan losses	0	0	0
Total	3,858	4,230
Loans individually evaluated for impairment related to recorded investment (loan balance)	0	0	0
Loans collectively evaluated for impairment related to recorded investment (loan balance)	0	0	0
Loans acquired with deteriorated credit quality related to recorded investment (loan balance)	0	0	0
Total loans	$0	$0	$0

Loans_Textual_Details

Loans (Textual) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
	Loans
	Tenants
	BaordOfDirectors
	Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Acquired with Deteriorated Credit Quality	$0	$500,000	$500,000
Loans (Textual) [Abstract]
Number of portfolio segment	2
Number of classes of loans	7
Number of minimum tenants under lease of non-owner occupied commercial real estate	1
Number of members of the board of directors in loan committee	8
Minimum due period of loans consider in a nonperforming status	90 days
Total nonaccrual TDR loans	37,300,000	37,200,000	44,400,000
Difference between recorded investment and unpaid principal balance of loan	29,700,000	30,600,000	21,700,000
Confirmed losses (partial charge-offs)	14,800,000	15,400,000	17,800,000
Fair value of discount adjustment	14,900,000	15,200,000	3,900,000
Acquired impaired loans	11,200,000	19,900,000	11,500,000
Performing trouble debt restructuring under impaired loans	46,000,000	45,700,000	41,800,000
Financing receivable allowance for acquired loans		500,000	500,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications from Nonaccretable Difference	0
Residential Mortgage Loans in Process of Foreclosure	2,200,000
Commercial Loan Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Acquired with Deteriorated Credit Quality	0	0	0
Loans (Textual) [Abstract]
Minimum value of loan requires executive and senior officer approval	1,500,000
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Acquired with Deteriorated Credit Quality	0	500,000	500,000
Loans (Textual) [Abstract]
Maximum due period of loans consider in performing status	90 days
Minimum due period of loans consider in a nonperforming status	90 days
Commercial [Member]
Loans (Textual) [Abstract]
Minimum value of loan requires group loan authority approval	1,000,000
Maximum value of loan requires executive and senior officer approval	3,500,000
Increase in Minimum Value of Loans Requiring Group Loan Authority Approval	5,000,000
Real Estate Residential Loans [Member]
Loans (Textual) [Abstract]
Period for loan secured under real estate residential security	15 years
Loan-to-value ratio at the time of origination	80.00%
Land Development Loans [Member]
Loans (Textual) [Abstract]
Maximum period for payment of loan	12 months
Maximum [Member] | Commercial Loan Portfolio [Member]
Loans (Textual) [Abstract]
Maximum value of loan requires group loan authority approval	10,000,000
Other loans requiring director loan committee approval depending on risk rating and credit action required	10,000,000
Maximum [Member] | Real Estate Residential Loans [Member]
Loans (Textual) [Abstract]
Upper limit of number of family residential properties	4
Minimum [Member] | Commercial Loan Portfolio [Member]
Loans (Textual) [Abstract]
Minimum value of loan requires group loan authority approval	1,000,000
Minimum value of loans depending on risk rating and requires credit action from board of directors	15,000,000
Minimum [Member] | Commercial [Member]
Loans (Textual) [Abstract]
Minimum value of loans requiring only director loan committee approval	$10,000,000
Minimum [Member] | Real Estate Residential Loans [Member]
Loans (Textual) [Abstract]
Lower limit of number of family residential properties	1

Intangible_Assets_Net_Carrying

Intangible Assets (Net Carrying Value) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Net carrying value of intangible assets
Goodwill	$180,128	$180,128	$120,164
Other intangible assets:
Total other intangible assets	31,655	33,080	12,872
Core deposit intangible assets [Member]
Other intangible assets:
Total other intangible assets	20,072	20,863	9,556
Mortgage servicing rights [Member]
Other intangible assets:
Total other intangible assets	$11,583	$12,217	$3,316	$3,423

Intangible_Assets_Amortization

Intangible Assets (Amortization Expense of Core Deposit Intangible Assets) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Carrying amount	$31,655	$12,872	$33,080
Amortization of intangible assets	1,825	695
Core deposit intangible assets [Member]
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Gross original amount	30,122	18,659	31,550
Accumulated amortization	10,050	9,103	10,687
Carrying amount	20,072	9,556	20,863
Amortization of intangible assets	$791	$445

Intangible_Assets_Carrying_and

Intangible Assets (Carrying and Fair Value of MSRs) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Net carrying value, fair value of MSRs and loans Corporation servicing for others
Loans serviced for others that have servicing rights capitalized	$2,062,544	$2,093,140	$877,530
Mortgage servicing rights [Member]
Net carrying value, fair value of MSRs and loans Corporation servicing for others
Net carrying value of MSRs	11,583	12,217	3,316
Fair value of MSRs	$14,378	$14,979	$6,706

Intangible_Assets_Activity_for

Intangible Assets (Activity for Capitalized MSRs) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Capitalized MSRs [Roll Forward]
Balance at beginning of period	$33,080
Amortization	-1,825	-695
Balance at end of period	31,655	12,872
Mortgage servicing rights [Member]
Capitalized MSRs [Roll Forward]
Balance at beginning of period	12,217	3,423
Additions	400	143
Amortization	-1,034	-250
Balance at end of period	$11,583	$3,316

Intangible_Assets_Textual_Deta

Intangible Assets (Textual) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Core deposit intangible assets [Member]
Estimated Future Amortization Expense, Fiscal Year Maturity [Abstract]
2015	$2,400,000
2016	2,900,000
2017	2,600,000
2018	2,500,000
2019	2,400,000
2020 and thereafter	7,200,000
Mortgage servicing rights [Member]
Intangible Assets (Textual) [Abstract]
Impairment valuation allowance	$200,000	$200,000	$0

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Loss (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Components of accumulated other comprehensive loss, net of related tax benefit/expense
Net unrealized gains (losses) on investment securities – available-for-sale, net of related tax expense (benefit) of $946 at March 31, 2015, $(113) at December 31, 2014 and $(478) at March 31, 2014	$1,758	($210)	($887)
Pension and other postretirement benefits adjustment, net of related tax benefit of $16,981 at March 31, 2015, $17,362 at December 31, 2014 and $9,915 at March 31, 2014	-31,537	-32,243	-18,414
Accumulated other comprehensive loss	($29,779)	($32,453)	($19,301)

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Loss (Textual) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Accumulated Other Comprehensive Loss (Textual) [Abstract]
Net unrealized gains (losses) on investment securities-available-for-sale, tax expense (benefit)	$946	($113)	($478)
Pension and other postretirement benefits adjustment, tax benefit	$16,981	$17,362	$9,915

Regulatory_Capital_Details

Regulatory Capital (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk weighted assets	$5,580,000,000	$5,700,000,000	$4,760,000,000
Chemical Financial Corporation [Member]
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	727,090,000	705,130,000	659,644,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	446,173,000	456,302,000	381,146,000
Actual, Ratio	13.00%	12.40%	13.80%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets:
Actual, Capital Amount	657,307,000	633,779,000	599,856,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	334,630,000	228,151,000	190,573,000
Actual, Ratio	11.80%	11.10%	12.60%
Minimum Required for Capital Adequacy Purposes, Ratio	6.00%	4.00%	4.00%
Common Equity Tier One Risk Based Capital	657,307,000
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	11.80%
Common Equity Tier One Risk Based Capital for Capital Adequacy	250,972,000
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%
Leverage Ratio:
Actual, Capital Amount	657,307,000	633,779,000	599,856,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	289,948,000	273,226,000	243,070,000
Actual, Ratio	9.10%	9.30%	9.90%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Chemical Bank [Member]
Total Capital to Risk-Weighted Assets:
Actual, Capital Amount	676,488,000	654,031,000	589,254,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	445,471,000	455,633,000	380,542,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	556,838,000	569,541,000	475,678,000
Actual, Ratio	12.10%	11.50%	12.40%
Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%	8.00%
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	606,813,000	582,783,000	529,560,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	334,103,000	227,816,000	190,271,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	445,471,000	341,725,000	285,407,000
Actual, Ratio	10.90%	10.20%	11.10%
Minimum Required for Capital Adequacy Purposes, Ratio	6.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	8.00%	6.00%	6.00%
Common Equity Tier One Risk Based Capital	606,813,000
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	10.90%
Common Equity Tier One Risk Based Capital for Capital Adequacy	250,577,000
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%
Common Equity Tier One Risk Based Capital to be Well Capitalized	361,945,000
Common Equity Tier One Risk Based Capital Required to Be Well Capitalized to Risk Weighted Assets	6.50%
Leverage Ratio:
Actual, Capital Amount	606,813,000	582,783,000	529,560,000
Minimum Required for Capital Adequacy Purposes, Capital Amount	289,840,000	273,048,000	242,939,000
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Capital Amount	$362,300,000	$341,310,000	$303,673,000
Actual, Ratio	8.40%	8.50%	8.70%
Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%	4.00%
Required to be Well Capitalized Under Prompt Corrective Action Regulations, Ratio	5.00%	5.00%	5.00%

Fair_Value_Measurements_Fair_V

Fair Value Measurements (Fair Value of Assets on a Recurring Basis) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	$680,644	$748,864	$657,818
Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	680,644	748,864	657,818
Loans Held-for-sale	9,675	9,128	3,814
Total assets measured at fair value on a recurring basis	690,319	757,992	661,632
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	8,302	8,259	0
Loans Held-for-sale	0	0	0
Total assets measured at fair value on a recurring basis	8,302	8,259	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	672,342	740,605	657,818
Loans Held-for-sale	9,675	9,128	3,814
Total assets measured at fair value on a recurring basis	682,017	749,733	661,632
Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Loans Held-for-sale	0	0	0
Total assets measured at fair value on a recurring basis	0	0	0
US Treasury Securities [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	8,302	8,259
US Treasury Securities [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	8,302	8,259
US Treasury Securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	8,302	8,259
US Treasury Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
US Treasury Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Government sponsored agencies [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	250,430	263,503	91,610
Government sponsored agencies [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	250,430	263,503	91,610
Government sponsored agencies [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Government sponsored agencies [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	250,430	263,503	91,610
Government sponsored agencies [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
State and political subdivisions [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	32,322	46,227	43,777
State and political subdivisions [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	32,322	46,227	43,777
State and political subdivisions [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
State and political subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	32,322	46,227	43,777
State and political subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Residential mortgage-backed securities [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	219,601	239,807	288,738
Residential mortgage-backed securities [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	219,601	239,807	288,738
Residential mortgage-backed securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Residential mortgage-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	219,601	239,807	288,738
Residential mortgage-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Collateralized mortgage obligations [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	133,300	144,383	166,719
Collateralized mortgage obligations [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	133,300	144,383	166,719
Collateralized mortgage obligations [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Collateralized mortgage obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	133,300	144,383	166,719
Collateralized mortgage obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Corporate bonds [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	34,997	45,095	65,415
Corporate bonds [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	34,997	45,095	65,415
Corporate bonds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Corporate bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	34,997	45,095	65,415
Corporate bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Preferred stock [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,692	1,590	1,559
Preferred stock [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,692	1,590	1,559
Preferred stock [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0	0
Preferred stock [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,692	1,590	1,559
Preferred stock [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	$0	$0	$0

Fair_Value_Measurements_Fair_V1

Fair Value Measurements (Fair Value of Assets on a Nonrecurring Basis) (Details) (Fair Value Measurements Nonrecurring [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	$46,589	$44,219	$39,517
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0	0
Significant Other Observable Inputs (Level 2) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0	0
Significant Unobservable Inputs (Level 3) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	46,589	44,219	39,517
Impaired originated loans [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	23,730	21,323	29,461
Impaired originated loans [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0	0
Impaired originated loans [Member] | Significant Other Observable Inputs (Level 2) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0	0
Impaired originated loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	23,730	21,323	29,461
Other real estate/repossessed assets [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	14,744	14,205	10,056
Other real estate/repossessed assets [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0	0
Other real estate/repossessed assets [Member] | Significant Other Observable Inputs (Level 2) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0	0
Other real estate/repossessed assets [Member] | Significant Unobservable Inputs (Level 3) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	14,744	14,205	10,056
Mortgage Servicing Rights [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	8,115	8,691
Mortgage Servicing Rights [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0
Mortgage Servicing Rights [Member] | Significant Other Observable Inputs (Level 2) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	0	0
Mortgage Servicing Rights [Member] | Significant Unobservable Inputs (Level 3) [Member]
Summary of assets measured at fair value on a nonrecurring basis
Total assets measured at fair value on a nonrecurring basis	$8,115	$8,691

Fair_Value_Measurements_Schedu

Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Investment securities:
Available-for-sale	$680,644	$748,864	$657,818
Held-to-maturity	380,176	315,740	272,407
Carrying Amount [Member]
Investment securities:
Nonmarketable equity securities	31,249	27,369	25,572
Carrying Amount [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	393,938	183,020	382,385
Investment securities:
Available-for-sale	8,302	8,259	0
Carrying Amount [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	672,342	740,605	657,818
Held-to-maturity	370,950	305,913	267,599
Loans Held-for-sale	9,675	9,128	3,814
Interest receivable	19,816	17,492	16,945
Liabilities:
Deposits without defined maturities	4,988,268	4,741,024	3,868,700
Interest payable	779	755	876
Short-term borrowings	372,236	389,467	361,231
Carrying Amount [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	10,500	10,500	10,500
Net loans	5,627,618	5,612,547	4,674,816
Liabilities:
Time deposits	1,332,085	1,337,947	1,362,593
Fair Value [Member]
Investment securities:
Nonmarketable equity securities	31,249	27,369	25,572
Fair Value [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	393,938	183,020	382,385
Investment securities:
Available-for-sale	8,302	8,259	0
Fair Value [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	672,342	740,605	657,818
Held-to-maturity	372,876	308,650	265,947
Loans Held-for-sale	9,675	9,128	3,814
Interest receivable	19,816	17,492	16,945
Liabilities:
Deposits without defined maturities	4,988,268	4,741,024	3,868,700
Interest payable	779	755	876
Short-term borrowings	372,236	389,467	361,231
Fair Value [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	7,300	7,090	6,460
Net loans	5,633,217	5,623,454	4,688,814
Liabilities:
Time deposits	$1,335,605	$1,340,015	$1,371,312

Fair_Value_Measurements_Textua

Fair Value Measurements (Textual) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Fair Value Measurements (Textual) [Abstract]
Impairment of goodwill	$0	$0	$0
Valuation Allowance on Mortgage Servicing Rights	200,000	200,000
Core deposit intangible assets [Member]
Fair Value Measurements (Textual) [Abstract]
Impairment identified for intangible assets	0	0	0
Maximum [Member]
Fair Value Measurements (Textual) [Abstract]
Expected life of intangible assets	15 years
Minimum [Member]
Fair Value Measurements (Textual) [Abstract]
Expected life of intangible assets	10 years
Total Impaired Loans [Member] | Maximum [Member]
Fair Value Measurements (Textual) [Abstract]
Percentage of discount factors used to determine fair value	80.00%
Total Impaired Loans [Member] | Minimum [Member]
Fair Value Measurements (Textual) [Abstract]
Percentage of discount factors used to determine fair value	70.00%
Other Real Estate and Repossessed Assets [Member] | Maximum [Member]
Fair Value Measurements (Textual) [Abstract]
Percentage of discount factors used to determine fair value	75.00%
Other Real Estate and Repossessed Assets [Member] | Minimum [Member]
Fair Value Measurements (Textual) [Abstract]
Percentage of discount factors used to determine fair value	70.00%
Fair Value Measurements Recurring [Member]
Fair Value Measurements (Textual) [Abstract]
Liabilities recorded at fair value	0	0	0
Fair Value Measurements Nonrecurring [Member]
Fair Value Measurements (Textual) [Abstract]
Liabilities recorded at fair value	$0	$0	$0

Earnings_Per_Common_Share_Deta

Earnings Per Common Share (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Numerator and denominator of the basic and diluted earnings per common share computations
Numerator for both basic and diluted earnings per common share, net income	$17,835	$13,813
Denominator for basic earnings per common share, weighted average common shares outstanding	32,809,000	29,825,000
Weighted average common stock equivalents	235,000	212,000
Denominator for diluted earnings per common share	33,044,000	30,037,000
Basic earnings per common share (dollars per share)	$0.54	$0.46
Diluted earnings per common share (dollars per share)	$0.54	$0.46
Stock Option [Member]
Earnings Per Common Share (Textual) [Abstract]
Average number of exercisable employee stock option awards that were not included in the computation of diluted earnings per common share	121,050	259,288

ShareBased_Compensation_Stock_

Share-Based Compensation (Stock Option Activity) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted average fair value of options granted	$8.40
Stock Options [Member] | Non Vested [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance, Number of Options	432,199
Granted, Number of Options	244,165
Exercised, Number of Options	0
Vested, Number of Options	-150,224
Forfeited/expired, Number of Options	-3,049
Ending balance, Number of Options	523,091
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Beginning balance, Weighted Average Exercise Price	$26.75
Granted, Weighted Average Exercise Price	$30.18
Exercised, Weighted Average Exercise Price	$0
Vested, Weighted Average Exercise Price	$25.57
Forfeited/expired, Weighted Average Exercise Price	$27.42
Ending balance, Weighted Average Exercise Price	$28.69
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]
Beginning balance, Weighted average grant date fair value	$8.30
Weighted average fair value of options granted	$8.40
Exercised, Weighted Average Grant Date Fair Value	$0
Vested, Weighted Average Grant Date Fair Value	$7.80
Forfeited/expired, Weighted Average Grant Date Fair Value	$8.59
Ending balance, Weighted average grant date fair value	$8.49
Stock Options [Member] | Vested & Nonvested [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance, Number of Options	1,037,311
Granted, Number of Options	244,165
Exercised, Number of Options	-37,191
Vested, Number of Options	0
Forfeited/expired, Number of Options	-3,049
Ending balance, Number of Options	1,241,236
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Beginning balance, Weighted Average Exercise Price	$25.90
Granted, Weighted Average Exercise Price	$30.18
Exercised, Weighted Average Exercise Price	$23.11
Vested, Weighted Average Exercise Price	$0
Forfeited/expired, Weighted Average Exercise Price	$27.42
Ending balance, Weighted Average Exercise Price	$26.82
Stock Options [Member] | Vested [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]
Exercisable/vested, Number of Options	718,145
Exercisable/vested, Weighted Average Exercise Price	$25.46

ShareBased_Compensation_BlackS

Share-Based Compensation (Black-Scholes Pricing Model Assumptions) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Assumptions of Black-Scholes option pricing model
Expected dividend yield	3.50%
Risk-free interest rate	1.78%
Expected stock price volatility	39.10%
Expected life of options - in years	7 years 0 months 0 days
Weighted average fair value of options granted	$8.40

ShareBased_Compensation_Restri

Share-Based Compensation (Restricted Stock Unit Activity) (Details) (Restricted Stock Units (RSUs) [Member], USD $)	3 Months Ended
	Mar. 31, 2015
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Number of Shares [Roll Forward]
Beginning balance, Number of shares	204,319
Granted, Number of shares	76,286
Converted into shares of common stock, Number of shares	-66,769
Forfeited/expired, Number of shares	-405
Ending balance, Number of shares	213,431
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, Weighted average grant date fair value	$24.14
Granted, Weighted Average grant date fair value	$28.15
Converted into shares of common stock, Weighted average grant date fair value	$22.32
Forfeited/expired, Weighted average grant date fair value	$25.17
Ending balance, Weighted average grant date fair value	$26.14

Textual_Details

(Textual) (Details) (USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Apr. 20, 2015
Share-Based Compensation Plans (Textual) [Abstract]
Share-based compensation expense	$0.80	$0.60
Restricted Stock Units (RSUs) [Member]
Share-Based Compensation Plans (Textual) [Abstract]
Corporation granted options to purchase restricted stock performance units	76,286
Unrecognized compensation expense	4.1
Unrecognized compensation expense, period for recognition	3 years 0 months 0 days
Restricted Stock Units (RSUs) [Member] | Maximum [Member]
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 Units (RSUs) [Member] | Minimum [Member]
Share-Based Compensation Plans (Textual) [Abstract]
Restricted stock performance units eligible to vest as a multiple of number of units granted	0.25
Equity Option [Member]
Share-Based Compensation Plans (Textual) [Abstract]
Common stock available for future grants under share-based compensation plans	32,953
Weighted-average remaining contractual terms for outstanding stock options	6 years 7 months 6 days
Weighted-average remaining contractual terms for exercisable stock options	4 years 8 months 12 days
Outstanding in-the-money stock options, intrinsic value	5.7
Exercisable in-the-money stock options, intrinsic value	4.4
Closing price of common stock	$31.36
Unrecognized compensation expense	$4.40
Unrecognized compensation expense, period for recognition	4 years 2 months 11 days
Shareholder Approved Proposal [Member]
Share-Based Compensation Plans (Textual) [Abstract]
Common stock available for future grants under share-based compensation plans			1,300,000

Pension_and_Other_Postretireme2

Pension and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost (Income)) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Defined Benefit Pension Plans [Member]
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan
Service cost	$273	$250
Interest cost	1,332	1,312
Expected return on plan assets	-2,161	-2,078
Amortization of prior service cost	-1	0
Amortization of unrecognized net loss (gain)	1,056	569
Net periodic benefit cost	499	53
Postretirement Benefit Plan [Member]
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan
Service cost	4	5
Interest cost	33	35
Amortization of prior service cost	32	32
Amortization of unrecognized net loss (gain)	0	-26
Net periodic benefit cost	$69	$46

Pension_and_Other_Postretireme3

Pension and Other Postretirement Benefit Plans (Textual) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Contribution to corporation's pension plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution to defined benefit pension plan		$0
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.15%
Chemical Financial Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of eligible pay contribution to certain employees	4.00%
Defined Contribution Plan, Employer Total Contribution Amount	$1.10	$0.80

Financial_Guarantees_Textual_D

Financial Guarantees (Textual) (Details) (Financial Standby Letter of Credit [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Financial Standby Letter of Credit [Member]
Financial Guarantees (Textual) [Abstract]
Letters of credit outstanding	$38	$41	$45
Expiration period for letters of credit, maximum	5 years