First Midwest Bancorp (ONBPP) 10-K 28 Feb 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	FIRST MIDWEST BANCORP INC
Entity Central Index Key	702,325
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2,331,611,351
Entity Common Stock, Shares Outstanding		103,007,554

Consolidated Statements of Fina

Consolidated Statements of Financial Condition - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 192,800	$ 155,055
Interest-bearing deposits in other banks	153,770	107,093
Trading securities, at fair value	20,447	17,920
Securities available-for-sale, at fair value	1,884,209	1,919,450
Securities held-to-maturity, at amortized cost (fair value 2017 – $12,013; 2016 – $18,212)	13,760	22,291
Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) stock, at cost	69,708	59,131
Loans	10,437,812	8,254,145
Allowance for loan losses	(95,729)	(86,083)
Net loans	10,342,083	8,168,062
Other real estate owned (OREO)	20,851	26,083
Premises, furniture, and equipment, net	123,316	82,577
Investment in bank-owned life insurance (BOLI)	279,900	219,746
Goodwill and other intangible assets	754,757	366,876
Accrued interest receivable and other assets	221,451	278,271
Total assets	14,077,052	11,422,555
Liabilities
Noninterest-bearing deposits	3,576,190	2,766,748
Interest-bearing deposits	7,477,135	6,061,855
Total deposits	11,053,325	8,828,603
Borrowed funds	714,884	879,008
Senior and subordinated debt	195,170	194,603
Accrued interest payable and other liabilities	248,799	263,261
Total liabilities	12,212,178	10,165,475
Stockholders' Equity
Common stock	1,123	913
Additional paid-in capital	1,031,870	498,937
Retained earnings	1,074,990	1,016,674
Accumulated other comprehensive loss, net of tax	(33,036)	(40,910)
Treasury stock, at cost	(210,073)	(218,534)
Total stockholders' equity	1,864,874	1,257,080
Total liabilities and stockholders' equity	$ 14,077,052	$ 11,422,555

Consolidated Statements of Fin3

Consolidated Statements of Financial Condition (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Securities held-to-maturity, at fair value	$ 12,013	$ 18,212
Preferred stock, shares authorized	1,000,000	1,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	150,000,000
Common stock, shares issued	112,351,000	91,284,000
Common stock, shares outstanding	102,717,000	81,325,000
Treasury stock, shares	9,634,000	9,959,000

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Income
Loans	$ 463,331	$ 337,998	$ 300,303
Investment securities – taxable	35,569	28,724	18,082
Investment securities – tax-exempt	6,296	8,737	13,861
Other short-term investments	4,520	2,873	3,738
Total interest income	509,716	378,332	335,984
Interest Expense
Deposits	16,184	9,863	9,527
Borrowed funds	9,100	6,313	2,314
Senior and subordinated debt	12,428	12,465	12,545
Total interest expense	37,712	28,641	24,386
Net interest income	472,004	349,691	311,598
Provision for loan losses	31,290	30,983	21,152
Net interest income after provision for loan losses	440,714	318,708	290,446
Noninterest Income
Service charges on deposit accounts	48,368	40,665	39,979
Wealth management fees	41,321	33,071	29,162
Card-based fees	28,992	29,104	26,984
Merchant servicing fees	10,340	12,533	11,739
Capital market products income	8,171	10,024	4,806
Mortgage banking income	8,131	10,162	5,741
Other service charges, commissions, and fees	9,843	9,542	8,848
BOLI income	5,946	3,647	4,185
Net securities (losses) gains	(1,876)	1,420	2,373
Other income	3,913	3,635	2,764
Net gain on sale-leaseback transaction	0	5,509	0
Total noninterest income	163,149	159,312	136,581
Noninterest Expense
Salaries and wages	182,507	151,341	133,739
Retirement and other employee benefits	41,886	33,309	31,852
Net occupancy and equipment expense	49,751	41,154	38,720
Professional services	33,689	25,122	22,720
Technology and related costs	18,068	14,765	14,581
Federal Deposit Insurance Corporation (FDIC) premiums	8,987	6,268	6,017
Advertising and promotions	8,694	7,787	7,606
Merchant card expense	8,377	10,782	9,886
Cardholder expense	7,323	5,812	5,243
Net OREO expense	4,683	3,024	5,281
Other expenses	31,821	24,834	21,601
Acquisition and integration related expenses	20,123	14,352	1,389
Lease cancellation fee	0	950	0
Property valuation adjustments	0	0	8,581
Total noninterest expense	415,909	339,500	307,216
Income before income tax expense	187,954	138,520	119,811
Income tax expense	89,567	46,171	37,747
Net income	$ 98,387	$ 92,349	$ 82,064
Per Common Share Data
Basic earnings per common share (in dollars per share)	$ 0.96	$ 1.14	$ 1.05
Diluted earnings per common share (in dollars per share)	$ 0.96	$ 1.14	$ 1.05
Weighted-average common shares outstanding (in shares)	101,423	79,797	77,059
Weighted-average diluted common shares outstanding (in shares)	101,443	79,810	77,072

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 98,387	$ 92,349	$ 82,064
Unrealized holding gains (losses):
Before tax	12,641	(19,204)	(9,824)
Tax effect	(5,077)	7,682	3,906
Net of tax	7,564	(11,522)	(5,918)
Reclassification of net (losses) gains included in net income:
Before tax	(1,876)	1,420	2,373
Tax effect	771	(568)	(970)
Net of tax	(1,105)	852	1,403
Net unrealized holding gains (losses)	8,669	(12,374)	(7,321)
Derivative Instruments
Before tax	(4,333)	2,175	(2,233)
Tax effect	1,746	(883)	903
Net of tax	(2,587)	1,292	(1,330)
Net unrealized holding gains (losses)
Before tax	2,988	(2,002)	(6,570)
Tax effect	(1,196)	563	2,687
Net of tax	1,792	(1,439)	(3,883)
Total other comprehensive income (loss)	7,874	(12,521)	(12,534)
Total comprehensive income	$ 106,261	$ 79,828	$ 69,530

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income - AOCI - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive (loss) income	$ 7,874	$ (12,521)	$ (12,534)
Accumulated Unrealized Loss on Securities Available- for-Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(22,645)	(10,271)	(2,950)
Other comprehensive (loss) income	8,669	(12,374)	(7,321)
Ending balance	(13,976)	(22,645)	(10,271)
Accumulated Unrealized Loss on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,176)	(2,468)	(1,138)
Other comprehensive (loss) income	(2,587)	1,292	(1,330)
Ending balance	(3,763)	(1,176)	(2,468)
Unrecognized Net Pension Costs
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(17,089)	(15,650)	(11,767)
Other comprehensive (loss) income	1,792	(1,439)	(3,883)
Ending balance	(15,297)	(17,089)	(15,650)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(40,910)	(28,389)	(15,855)
Other comprehensive (loss) income	7,874	(12,521)	(12,534)
Ending balance	$ (33,036)	$ (40,910)	$ (28,389)

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders’ Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning balance at Dec. 31, 2014	$ 1,100,775	$ 882	$ 449,798	$ 899,516	$ (15,855)	$ (233,566)
Beginning balance (in shares) at Dec. 31, 2014		77,695
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	82,064			82,064
Other comprehensive (loss) income	(12,534)				(12,534)
Common dividends declared ($0.36, $0.36 and $0.39)	(28,064)			(28,064)
Purchase of treasury stock	(120)					(120)
Purchase of treasury stock (in shares)		(7)
Acquisition, net of issuance costs	0
Restricted stock activity	(3,296)		(10,236)			6,940
Restricted stock activity (in shares)		267
Treasury stock issued to benefit plans	(201)		(132)			(333)
Treasury stock issued to benefit plans (in shares)		(3)
Share-based compensation expense	7,242		7,242
Ending balance at Dec. 31, 2015	1,146,268	$ 882	446,672	953,516	(28,389)	(226,413)
Ending balance (in shares) at Dec. 31, 2015		77,952
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	92,349			92,349
Other comprehensive (loss) income	(12,521)				(12,521)
Common dividends declared ($0.36, $0.36 and $0.39)	(29,191)			(29,191)
Acquisition, net of issuance costs	54,896	$ 31	54,865
Acquisition, net of issuance costs (in shares)		3,042
Common stock issued	227		227
Common stock issued (in shares)		13
Restricted stock activity	(2,673)		(10,685)			8,012
Restricted stock activity (in shares)		326
Treasury stock issued to benefit plans	(154)		(21)			(133)
Treasury stock issued to benefit plans (in shares)		(8)
Share-based compensation expense	7,879		7,879
Ending balance at Dec. 31, 2016	$ 1,257,080	$ 913	498,937	1,016,674	(40,910)	(218,534)
Ending balance (in shares) at Dec. 31, 2016	81,325	81,325
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 98,387			98,387
Other comprehensive (loss) income	7,874				7,874
Common dividends declared ($0.36, $0.36 and $0.39)	(40,071)			(40,071)
Acquisition, net of issuance costs	534,090	$ 210	533,322			558
Acquisition, net of issuance costs (in shares)		21,078
Common stock issued	240		240
Common stock issued (in shares)		9
Restricted stock activity	(3,659)		(11,855)			8,196
Restricted stock activity (in shares)		317
Treasury stock issued to benefit plans	(290)		(3)			(293)
Treasury stock issued to benefit plans (in shares)		(12)
Share-based compensation expense	11,223		11,223
Ending balance at Dec. 31, 2017	$ 1,864,874	$ 1,123	$ 1,031,870	$ 1,074,990	$ (33,036)	$ (210,073)
Ending balance (in shares) at Dec. 31, 2017	102,717	102,717

Consolidated Statements of Cha8

Consolidated Statements of Changes in Stockholders’ Equity (Parentheticals) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock
Common dividends declared per common share (in dollars per share)	$ 0.39	$ 0.36	$ 0.36

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities
Net income		$ 98,387	$ 92,349	$ 82,064
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses		31,290	30,983	21,152
Depreciation of premises, furniture, and equipment		13,995	12,804	13,367
Net amortization of premium on securities		16,142	13,653	4,849
Net securities losses (gains)		1,876	(1,420)	(2,373)
Gains on sales of 1-4 family mortgages and corporate loans held-for-sale		(7,078)	(8,931)	(6,847)
Net losses on sales and valuation adjustments of OREO		585	1,196	2,631
Amortization of the FDIC indemnification asset		1,208	1,185	1,461
Net (gains) losses		(125)	(4,762)	7,718
BOLI income		(5,946)	(3,647)	(4,185)
Net pension cost (income)		981	(513)	622
Share-based compensation expense	[1]	11,223	7,879	7,242
Tax benefit (expense) related to share-based compensation		349	(197)	(406)
Provision for deferred income tax (benefit) expense		(4,077)	(1,367)	16,897
Amortization of other intangible assets		7,865	4,682	3,920
Originations of mortgage loans held-for-sale		(254,030)	(238,192)	(158,699)
Proceeds from sales of mortgage loans held-for-sale		258,626	246,642	158,791
Net (increase) decrease in trading securities		(2,527)	(1,026)	566
Net decrease (increase) in accrued interest receivable and other assets		121,577	(76,902)	10,023
Net (decrease) increase in accrued interest payables and other liabilities		(55,762)	47,118	(1,042)
Net cash provided by operating activities		234,559	121,534	157,751
Investing Activities
Proceeds from maturities, repayments, and calls of securities available-for-sale		349,444	360,303	322,764
Proceeds from sales of securities available-for-sale		629,843	53,186	93,909
Purchases of securities available-for-sale		(733,440)	(933,317)	(509,481)
Proceeds from maturities, repayments, and calls of securities held-to-maturity		8,546	8,077	4,645
Purchases of securities held-to-maturity		(15)	(5,352)	(1,242)
Purchases of FHLB stock		(7,330)	(18,276)	(1,190)
Net increase in loans		(457,501)	(714,213)	(399,807)
Proceeds from claims on BOLI, net of premiums paid		1,722	1,588	1,082
Proceeds from sales of OREO		19,326	7,539	18,572
Proceeds from sales of premises, furniture, and equipment		18,031	152,863	1,230
Purchases of premises, furniture, and equipment		(16,123)	(19,083)	(11,269)
Net cash received from (paid for) acquisitions		41,717	57,347	(16,047)
Net cash used in investing activities		(145,780)	(1,049,338)	(496,834)
Financing Activities
Net increase in deposit accounts		200,848	135,944	118,167
Net (decrease) increase in borrowed funds		(164,124)	711,496	25,902
Purchase of treasury stock		0	0	(120)
Net proceeds from the issuance of subordinated debt		0	146,484	0
Payments for the retirement of senior and subordinated debt		0	(153,500)	0
Cash dividends paid		(37,129)	(29,198)	(27,036)
Restricted stock activity		(3,952)	(2,476)	(2,890)
Net cash (used in) provided by financing activities		(4,357)	808,750	114,023
Net increase (decrease) in cash and cash equivalents		84,422	(119,054)	(225,060)
Cash and cash equivalents at beginning of year		262,148	381,202	606,262
Cash and cash equivalents at end of year		346,570	262,148	381,202
Supplemental Disclosures of Cash Flow Information:
Income taxes paid		15,191	57,553	25,022
Interest paid to depositors and creditors		36,424	27,400	24,535
Dividends declared, but unpaid		10,185	7,243	7,250
Common stock issued for acquisitions, net of issuance costs		534,090	54,896	0
Non-cash transfers of loans to OREO		6,255	4,173	13,504
Non-cash transfers of loans held-for-investment to loans held-for-sale		$ 48,999	$ 93,981	$ 57,130
[1]	Comprised of restricted stock, restricted stock unit, and performance share awards expense.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations – First Midwest Bancorp, Inc. (the "Company") is a bank holding company that was incorporated in Delaware in 1982 and began operations on March 31, 1983. The Company is headquartered in Itasca, Illinois and has operations located primarily throughout the Chicago metropolitan area, as well as northwest Indiana, central and western Illinois, and eastern Iowa. The Company operates three wholly-owned subsidiaries: First Midwest Bank (the "Bank"), Catalyst Asset Holdings, LLC ("Catalyst"), and Premier Asset Management LLC ("Premier"). The Bank conducts the majority of the Company's operations, Catalyst manages certain non-performing assets of the Company, and Premier is a registered investment advisor providing advisory services to certain of the Company's wealth management clients. The Company is engaged in commercial and retail banking and offers a broad range of banking, treasury management, and wealth management products and services, tailored to the needs of its commercial and industrial, commercial real estate, municipal, and consumer customers. Basis of Presentation – The accounting and reporting policies of the Company and its subsidiaries conform to U.S. generally accepted accounting principles ("GAAP") and general practices within the banking industry. The Company uses the accrual basis of accounting for financial reporting purposes. Certain reclassifications were made to prior year amounts to conform to the current year presentation. Use of Estimates – The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates and assumptions are based on the best available information, actual results could differ from those estimates. Principles of Consolidation – The accompanying consolidated financial statements include the financial position and results of operations of the Company and its subsidiaries after elimination of all significant intercompany accounts and transactions. Assets held in a fiduciary or agency capacity are not assets of the Company or its subsidiaries and are not included in the consolidated financial statements. Segment Disclosures – The Company has one reportable segment. The Company's chief operating decision maker evaluates the operations of the Company using consolidated information for purposes of allocating resources and assessing performance. Therefore, segment disclosures are not required. The following is a summary of the Company's significant accounting policies. Business Combinations – Business combinations are accounted for under the acquisition method of accounting. Assets acquired and liabilities assumed are recorded at their estimated fair values as of the date of acquisition, with any excess of the purchase price of the acquisition over the fair value of the identifiable net tangible and intangible assets acquired recorded as goodwill. Alternatively, a gain is recorded if the fair value of assets purchased exceeds the fair value of liabilities assumed and consideration paid. The results of operations of the acquired business are included in the Consolidated Statements of Income from the effective date of the acquisition. Cash and Cash Equivalents – For purposes of the Consolidated Statements of Cash Flows, management defines cash and cash equivalents to include cash and due from banks, interest-bearing deposits in other banks, and other short-term investments, if any, such as federal funds sold and securities purchased under agreements to resell. Securities – Securities are classified as held-to-maturity, trading, or available-for-sale at the time of purchase. Securities Held-to-Maturity – Securities classified as held-to-maturity are securities for which management has the intent and ability to hold to maturity. These securities are stated at cost and adjusted for amortization of premiums and accretion of discounts over the estimated lives of the securities using the effective interest method. Trading Securities – The Company's trading securities consist of diversified investment securities held in a grantor trust under deferred compensation arrangements in which plan participants may direct amounts earned to be invested in securities other than Company stock. The accounts of the grantor trust are consolidated with the accounts of the Company in its consolidated financial statements. Trading securities are reported at fair value. Other than the securities held in the grantor trust, the Company does not carry any securities for trading purposes. Securities Available-for-Sale – All other securities are classified as available-for-sale. Securities available-for-sale are carried at fair value with unrealized gains and losses, net of related deferred income taxes, recorded in stockholders' equity as a separate component of accumulated other comprehensive loss. The historical cost of debt securities is adjusted for amortization of premiums and accretion of discounts over the estimated life of the security using the effective interest method. Amortization of premiums and accretion of discounts are included in interest income. Purchases and sales of securities are recognized on a trade date basis. Realized securities gains or losses are reported in net securities (losses) gains in the Consolidated Statements of Income. The cost of securities sold is based on the specific identification method. On a quarterly basis, the Company individually assesses securities with unrealized losses to determine whether there were any events or circumstances indicating that an other-than-temporary impairment ("OTTI") has occurred. In evaluating OTTI, the Company considers many factors, including (i) the severity and duration of the impairment, (ii) the financial condition and near-term prospects of the issuer, including external credit ratings and recent downgrades for debt securities, (iii) its intent to hold the security until its value recovers, and (iv) the likelihood that it will be required to sell the security before a recovery in value, which may be at maturity. If management intends to sell the security or believes it is more likely than not that it will be required to sell the security prior to full recovery, an OTTI charge will be recognized through income as a realized loss and included in net securities (losses) gains in the Consolidated Statements of Income. If management does not expect to sell the security or believes it is not more likely than not that it will be required to sell the security prior to full recovery, the OTTI is separated into the amount related to credit deterioration, which is recognized through income as a realized loss, and the amount resulting from other factors, which is recognized in other comprehensive income (loss). FHLB and FRB Stock – The Company, as a member of the FHLB and FRB, is required to maintain an investment in the capital stock of the FHLB and FRB. No ready market exists for these stocks, and they have no quoted market values. The stock is redeemable at par by the FHLB and FRB and is, therefore, carried at cost and periodically evaluated for impairment. Loans – Loans held-for-investment are loans that the Company intends to hold until they are paid in full and are carried at the principal amount outstanding, including certain net deferred loan origination fees. Loan origination fees, commitment fees, and certain direct loan origination costs are deferred, and the net amount is amortized as a yield adjustment over the contractual life of the related loans or commitments and included in interest income. Fees related to letters of credit are amortized into fee income over the contractual life of the commitment. Other credit-related fees are recognized as fee income when earned. The Company's net investment in direct financing leases is included in loans and consists of future minimum lease payments and estimated residual values, net of unearned income. Interest income on loans is accrued based on principal amounts outstanding. Loans held-for-sale are carried at the lower of aggregate cost or fair value and included in other assets in the Consolidated Statements of Financial Condition. Acquired and Covered Loans – Covered loans consist of loans acquired by the Company in FDIC-assisted transactions, which are covered by loss share agreements with the FDIC (the "FDIC Agreements"), under which the FDIC reimburses the Company for the majority of the losses and eligible expenses related to these assets during the coverage period. Acquired loans consist of all other loans that were acquired in business combinations that are not covered by the FDIC Agreements. Certain loans that were previously classified as covered loans are no longer covered under the FDIC Agreements, and are included in acquired loans. Covered loans and acquired loans are included within loans held-for-investment. Acquired and covered loans are separated into (i) non-purchased credit impaired ("non-PCI") and (ii) purchased credit impaired ("PCI") loans. Non-PCI loans include loans that did not have evidence of credit deterioration since origination at the acquisition date. PCI loans include loans that had evidence of credit deterioration since origination and for which it was probable at acquisition that the Company would not collect all contractually required principal and interest payments. Evidence of credit deterioration was evaluated using various indicators, such as past due and non-accrual status. Leases and revolving loans do not qualify to be accounted for as PCI loans and are accounted for as non-PCI loans. The acquisition adjustment related to non-PCI loans is amortized into interest income over the contractual life of the related loans. If an acquired non-PCI loan is renewed subsequent to the acquisition date, any remaining acquisition adjustment is accreted into interest income and the loan is considered a new loan that is no longer classified as an acquired loan. PCI loans are accounted for based on estimates of expected future cash flows. To estimate the fair value, the Company generally aggregates purchased consumer loans and commercial loans into pools of loans with common risk characteristics, such as delinquency status, credit score, and internal risk ratings. The fair values of larger balance commercial loans are estimated on an individual basis. Expected future cash flows in excess of the fair value of loans at the purchase date ("accretable yield") are recorded as interest income over the life of the loans if the timing and amount of the expected future cash flows can be reasonably estimated. The non-accretable yield represents the difference between contractually required payments and the expected future cash flows determined at acquisition. Subsequent increases in expected future cash flows are offset against the allowance for credit losses to the extent an allowance has been established or otherwise recognized as interest income prospectively. The present value of any decreases in expected future cash flows is recognized by recording a charge-off through the allowance for loan losses or providing an allowance for loan losses. 90-Days Past Due Loans – The Company's accrual of interest on loans is generally discontinued at the time the loan is 90 days past due unless the credit is sufficiently collateralized and in the process of renewal or collection. Non-accrual Loans – Generally, corporate loans are placed on non-accrual status (i) when either principal or interest payments become 90 days or more past due unless the credit is sufficiently collateralized and in the process of renewal or collection or (ii) when an individual analysis of a borrower's creditworthiness warrants a downgrade to non-accrual regardless of past due status. When a loan is placed on non-accrual status, unpaid interest credited to income in the current year is reversed, and unpaid interest accrued in prior years is charged against the allowance for loan losses. After the loan is placed on non-accrual status, all debt service payments are applied to the principal on the loan. Future interest income may only be recorded on a cash basis after recovery of principal is reasonably assured. Non-accrual loans are returned to accrual status when the financial position of the borrower and other relevant factors indicate that the Company will collect all principal and interest. Commercial loans and loans secured by real estate are charged-off when deemed uncollectible. A loss is recorded if the net realizable value of the underlying collateral is less than the outstanding principal and interest. Consumer loans that are not secured by real estate are subject to mandatory charge-off at a specified delinquency date and are usually not classified as non-accrual prior to being charged-off. Closed-end consumer loans, which include installment, automobile, and single payment loans, are usually charged-off no later than the end of the month in which the loan becomes 120 days past due. PCI loans are generally considered accruing loans unless reasonable estimates of the timing and amount of expected future cash flows cannot be determined. Loans without reasonable future cash flow estimates are classified as non-accrual loans, and interest income is not recognized on those loans until the timing and amount of the expected future cash flows can be reasonably determined. Troubled Debt Restructurings ("TDRs") – A restructuring is considered a TDR when (i) the borrower is experiencing financial difficulties, and (ii) the creditor grants a concession, such as forgiveness of principal, reduction of the interest rate, changes in payments, or extension of the maturity date. Loans are not classified as TDRs when the modification is short-term or results in an insignificant delay in payments. The Company's TDRs are determined on a case-by-case basis. The Company does not accrue interest on a TDR unless it believes collection of all principal and interest under the modified terms is reasonably assured. For a TDR to begin accruing interest, the borrower must demonstrate some level of past performance and the future capacity to perform under the modified terms. Generally, six months of consecutive payment performance under the restructured terms is required before a TDR is returned to accrual status. However, the period could vary depending on the individual facts and circumstances of the loan. An evaluation of the borrower's current creditworthiness is used to assess the borrower's capacity to repay the loan under the modified terms. This evaluation includes an estimate of expected future cash flows, evidence of strong financial position, and estimates of the value of collateral, if applicable. For TDRs to be removed from TDR status in the calendar year after the restructuring, the loans must (i) have an interest rate and terms that reflect market conditions at the time of restructuring, and (ii) be in compliance with the modified terms. If the loan was restructured at below market rates and terms, it continues to be separately reported as a TDR until it is paid in full or charged-off. Impaired Loans – Impaired loans consist of corporate non-accrual loans and TDRs. A loan is considered impaired when it is probable that the Company will not collect all contractual principal and interest. With the exception of accruing TDRs, impaired loans are classified as non-accrual and are exclusive of smaller homogeneous loans, such as home equity, 1-4 family mortgages, and installment loans. Impaired loans with balances under a specified threshold are not individually evaluated for impairment. For all other impaired loans, impairment is measured by comparing the estimated value of the loan to the recorded book value. The value of collateral-dependent loans is based on the fair value of the underlying collateral, less costs to sell. The value of other loans is measured using the present value of expected future cash flows discounted at the loan's initial effective interest rate. Allowance for Credit Losses – The allowance for credit losses is comprised of the allowance for loan losses and the reserve for unfunded commitments, and is maintained by management at a level believed adequate to absorb estimated losses inherent in the existing loan portfolio. Determination of the allowance for credit losses is subjective since it requires significant estimates and management judgment, including the amounts and timing of expected future cash flows on impaired loans, estimated losses on pools of homogeneous loans, consideration of current economic trends, and other factors. Loans deemed to be uncollectible are charged-off against the allowance for loan losses, while recoveries of amounts previously charged-off are credited to the allowance for loan losses. Additions to the allowance for loan losses are charged to expense through the provision for loan losses. The amount of provision depends on a number of factors, including net charge-off levels, loan growth, changes in the composition of the loan portfolio, and the Company's assessment of the allowance for loan losses based on the methodology discussed below. Allowance for Loan Losses – The allowance for loan losses consists of (i) specific reserves for individual loans where the recorded investment exceeds the value, (ii) an allowance based on a loss migration analysis that uses historical credit loss experience for each loan category, and (iii) an allowance based on other internal and external qualitative factors. The specific reserves component of the allowance for loan losses is based on a periodic analysis of impaired loans exceeding a fixed dollar amount. If the value of an impaired loan is less than the recorded book value, the Company either establishes a valuation allowance (i.e., a specific reserve) equal to the excess of the book value over the collateral value of the loan as a component of the allowance for loan losses or charges off the amount if it is a confirmed loss. The general reserve component is based on a loss migration analysis, which examines actual loss experience by loan category for a rolling 8-quarter period and the related internal risk rating for corporate loans. The loss migration analysis is updated quarterly primarily using actual loss experience. This component is then adjusted based on management's consideration of many internal and external qualitative factors, including: • Changes in the composition of the loan portfolio, trends in the volume of loans, and trends in delinquent and non-accrual loans that could indicate that historical trends do not reflect current conditions. • Changes in credit policies and procedures, such as underwriting standards and collection, charge-off, and recovery practices. • Changes in the experience, ability, and depth of credit management and other relevant staff. • Changes in the quality of the Company's loan review system and Board of Directors oversight. • The effect of any concentration of credit and changes in the level of concentrations, such as loan type or risk rating. • Changes in the value of the underlying collateral for collateral-dependent loans. • Changes in the national and local economy that affect the collectability of various segments of the portfolio. • The effect of other external factors, such as competition and legal and regulatory requirements, on the Company's loan portfolio. The allowance for loan losses also consists of an allowance on acquired and covered non-PCI and PCI loans. No allowance for loan losses is recorded on acquired loans at the acquisition date. Subsequent to the acquisition date, an allowance for credit losses is established as necessary to reflect credit deterioration. The acquired non-PCI allowance is based on management's evaluation of the acquired non-PCI loan portfolio giving consideration to the current portfolio balance including the remaining acquisition adjustments, maturity dates, and overall credit quality. The allowance for covered non-PCI loans is calculated in the same manner as the general reserve component based on a loss migration analysis as discussed above. The acquired and covered PCI allowance reflects the difference between the carrying value and the discounted expected future cash flows of the acquired and covered PCI loans. On a periodic basis, the adequacy of this allowance is determined through a re-estimation of expected future cash flows on all of the outstanding acquired and covered PCI loans using either a probability of default/loss given default ("PD/LGD") methodology or a specific review methodology. The PD/LGD model is a loss model that estimates expected future cash flows using a probability of default curve and loss given default estimates. Acquired non-PCI loans that have renewed subsequent to the respective acquisition dates are no longer classified as acquired loans. Instead, they are included in the general loan population and allocated an allowance based on a loss migration analysis. Reserve for Unfunded Commitments – The Company also maintains a reserve for unfunded commitments, including letters of credit, for the risk of loss inherent in these arrangements. The reserve for unfunded commitments is estimated using the loss migration analysis from the allowance for loan losses, adjusted for probabilities of future funding requirements. The reserve for unfunded commitments is included in other liabilities in the Consolidated Statements of Financial Condition. The establishment of the allowance for credit losses involves a high degree of judgment given the difficulty of assessing the factors impacting loan repayment and estimating the timing and amount of losses. While management utilizes its best judgment and information available, the adequacy of the allowance for credit losses depends on a variety of factors beyond the Company's control, including the performance of its loan portfolio, the economy, changes in interest rates and property values, and the interpretation of loan risk classifications by regulatory authorities. OREO – OREO consists of properties acquired through foreclosure in partial or total satisfaction of defaulted loans. At initial transfer into OREO, properties are recorded at fair value, less estimated selling costs. Subsequently, OREO is carried at the lower of the cost basis or fair value, less estimated selling costs. OREO write-downs occurring at the transfer date are charged against the allowance for loan losses, establishing a new cost basis. Subsequent to the initial transfer, the carrying values of OREO may be adjusted through a valuation allowance to reflect reductions in value resulting from new appraisals, new list prices, changes in market conditions, or changes in disposition strategies. Increases in value can be recognized through a reduction in the valuation allowance, but may not exceed the established cost basis. These valuation adjustments, along with expenses related to maintenance of the properties, are included in net OREO expense in the Consolidated Statements of Income. FDIC Indemnification Asset – The majority of loans and OREO acquired through FDIC-assisted transactions are covered by the FDIC Agreements, under which the FDIC reimburses the Company for the majority of the losses and eligible expenses related to these assets during the coverage period. The FDIC indemnification asset represents the present value of expected future reimbursements from the FDIC. Since the indemnified items are covered loans and covered OREO, which are initially measured at fair value, the FDIC indemnification asset is also initially measured at fair value by discounting the expected future cash flows to be received from the FDIC. These expected future cash flows are estimated by multiplying estimated losses on covered PCI loans and covered OREO by the reimbursement rates in the FDIC Agreements. The balance of the FDIC indemnification asset is adjusted periodically to reflect changes in expected future cash flows. Decreases in estimated reimbursements from the FDIC are recorded prospectively through amortization and increases in estimated reimbursements from the FDIC are recognized by an increase in the carrying value of the indemnification asset. Payments from the FDIC for reimbursement of losses result in a reduction of the FDIC indemnification asset. Depreciable Assets – Premises, furniture, and equipment are stated at cost, less accumulated depreciation. Depreciation expense is determined by the straight-line method over the estimated useful lives of the assets. Useful lives range from 3 to 10 years for furniture and equipment and 25 to 40 years for premises. Leasehold improvements are amortized over the shorter of the life of the asset or the lease term. Gains on dispositions are included in other noninterest income and losses on dispositions are included in other noninterest expense in the Consolidated Statements of Income. Maintenance and repairs are charged to operating expenses as incurred, while improvements that extend the useful life of assets are capitalized and depreciated over the estimated remaining life. Certain assets, such as buildings and land, that the Company intends to sell and meet held-for-sale criteria are transferred into the held-for-sale category at the lower of their fair value, as determined by a current appraisal, or their recorded investment. Long-lived depreciable assets are evaluated periodically for impairment when events or changes in circumstances indicate the carrying amount may not be recoverable. Impairment exists when the undiscounted expected future cash flows of a long-lived asset are less than its carrying value. In that event, the Company recognizes a loss for the difference between the carrying amount and the estimated fair value of the asset based on a quoted market price, if applicable, or a discounted cash flow analysis. Impairment losses are recorded in other noninterest expense in the Consolidated Statements of Income. BOLI – BOLI represents life insurance policies on the lives of certain Company directors and officers for which the Company is the sole owner and beneficiary. These policies are recorded as an asset in the Consolidated Statements of Financial Condition at their cash surrender value ("CSV") or the current amount that could be realized if settled. The change in CSV and insurance proceeds received are included as a component of noninterest income in the Consolidated Statements of Income. Goodwill and Other Intangible Assets – Goodwill represents the excess of the purchase price of the acquisition over the fair value of the net tangible and intangible assets acquired using the acquisition method of accounting. Goodwill is not amortized. Instead, impairment testing is conducted annually as of October 1 or more often if events or circumstances between annual tests indicate that there may be impairment. Impairment testing is performed using either a qualitative or quantitative approach at the reporting unit level. All of the Company's goodwill is allocated to First Midwest Bancorp, Inc., which is the Company's only applicable reporting unit for purposes of testing goodwill for impairment. The Company performs impairment testing using a qualitative approach to determine whether it is more-likely-than-not that the fair value of a reporting unit is less than its carrying amount. Qualitative factors include, but are not limited to, macroeconomic conditions, industry and market specific conditions and trends, the Company's financial performance, market capitalization, stock price, and Company-specific events relevant to the assessment. If the assessment of qualitative factors indicates that it is not more-likely-than-not that an impairment exists, no further testing is performed; otherwise, the Company would proceed with a quantitative two-step goodwill impairment test. In the first step, the Company compares its estimate of the fair value of the reporting unit, which is based on a discounted cash flow analysis, with its carrying amount, including goodwill. If the fair value of the reporting unit exceeds its carrying amount, goodwill of the reporting unit is not impaired and the second step is not required. If necessary, the second step compares the implied fair value of the reporting unit goodwill with the carrying amount of that goodwill. The implied fair value of goodwill is determined by assigning the value of the reporting unit to all of the assets and liabilities of that unit, including any other identifiable intangible assets. An impairment loss is recognized if the carrying amount of the reporting unit goodwill exceeds the implied fair value of goodwill. Other intangible assets represent purchased assets that lack physical substance, but can be distinguished from goodwill because of contractual or other legal rights or because the asset is capable of being sold or exchanged either on its own or in combination with a related contract, asset, or liability. Identified intangible assets that have a finite useful life are amortized over that life in a manner that reflects the estimated decline in the economic value of the identified intangible asset. All of the Company's other intangible assets have finite lives and are amortized over varying periods not exceeding 13 years. Intangible assets are reviewed for impairment annually or more frequently when events or circumstances indicate that its carrying amount may not be recoverable. Wealth Management – Assets held in a fiduciary or agency capacity for customers are not included in the consolidated financial statements as they are not assets of the Company or its subsidiaries. Fee income is recognized on an accrual basis and is included as a component of noninterest income in the Consolidated Statements of Income. Derivative Financial Instruments – To provide derivative products to customers and in the ordinary course of business, the Company enters into derivative transactions as part of its overall interest rate risk management strategy to minimize significant unplanned fluctuations in earnings and expected future cash flows caused by interest rate volatility. All derivative instruments are recorded at fair value as either other assets or other liabilities in the Consolidated Statements of Financial Condition. Subsequent changes in a derivative's fair value are recognized in earnings unless specific hedge accounting criteria are met. On the date the Company enters into a derivative contract, the derivative is designated as a fair value hedge, a cash flow hedge, or a non-hedge derivative instrument. Fair value hedges are designed to mitigate exposure to changes in the fair value of an asset or liability attributable to a particular risk, such as interest rate risk. Cash flow hedges are designed to mitigate exposure to variability in expected future cash flows to be received or paid related to an asset, liability, or other type of forecasted transaction. The Company formally documents all relationships between hedging instruments and hedged items, including its risk management objective and strategy at inception. At the hedge's inception and quarterly thereafter, a formal assessment is performed to determine the effectiveness of the derivative in offsetting changes in the fair values or expected future cash flows of the hedged items in the current period and prospectively. If a derivative instrument designated as a hedge is terminated or ceases to be highly effective, hedge accounting is discontinued prospectively, and the gain or loss is amortized into earnings. For fair value hedges, the gain or loss is amortized over the remaining life of the hedged asset or liability. For cash flow hedges, the gain or loss is amortized over the same period that the forecasted hedged transactions impact earnings. If the hedged item is disposed of, any fair value adjustments are included in the gain or loss from the disposition of the hedged item. If the forecasted transaction is no longer probable, the gain or loss is included in earnings immediately. For fair value hedges, changes in the fair value of the derivative instruments, as well as changes in the fair value of the hedged item, are recognized in earnings. For cash flow hedges, the effective portion of the change in fair value of the derivative instrument is reported as a component of accumulated other comprehensive loss and is reclassified to earnings when the hedged transaction is reflected in earnings. Ineffectiveness is calculated based on th

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Adopted Accounting Pronouncements Contingent Put and Call Options in Debt Instruments: In March of 2016, the Financial Accounting Standards Board ("FASB") issued final guidance clarifying the requirements for assessing whether contingent call (put) options that can accelerate the payment of principal on debt instruments are clearly and closely related to their debt hosts. Entities are required to apply the guidance to existing debt instruments (or hybrid financial instruments that are determined to have a debt host) using a modified retrospective transition method as of the period of adoption. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity. Equity Method Accounting: In March of 2016, the FASB issued final guidance to simplify the equity method of accounting. The guidance eliminates the requirement to retrospectively apply equity method accounting in previous periods when an investor initially obtains significant influence over an investee. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity. Accounting for Employee Share-based Payments: In March of 2016, the FASB issued guidance to simplify the accounting for employee share-based payment transactions. The guidance requires entities to recognize the income tax effects of awards in the income statement when the awards vest or are settled. In addition, the guidance allows entities to repurchase more of an employee's shares than it can under current guidance for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. The adoption of this guidance on January 1, 2017 resulted in a $638,000 tax benefit to the provision for income tax expense for the year ended December 31, 2017 , recorded in the Company's results of operations. The Company elected to estimate forfeitures, which is consistent with the Company's practice before the adoption of this guidance. Accounting Pronouncements Pending Adoption Revenue from Contracts with Customers: In May of 2014, the FASB issued guidance that requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In March of 2016, the FASB issued an amendment to this guidance to clarify the implementation of guidance on principal versus agent consideration. Additional amendments to clarify the implementation guidance on the identification of performance obligations and licensing were issued in April of 2016 and narrow-scope improvements and practical expedients were issued in May of 2016. The guidance was initially effective for annual and interim reporting periods beginning on or after December 15, 2016 but was deferred to December 15, 2017, and must be applied either retrospectively or using the modified retrospective approach. Early adoption is permitted, but not before the original effective date. The Company's revenue is comprised of net interest income on financial assets and liabilities, which is excluded from the scope of this guidance, and noninterest income. The primary sources of revenue within noninterest income are service charges on deposit accounts, wealth management fees, card-based fees, and merchant servicing fees. Based upon the Company's final assessment, this guidance will affect the presentation of merchant servicing fees, card-based fees, cardholder expenses, and merchant card expense that are currently presented on a gross basis within noninterest income and noninterest expense but will now be required to be presented on a net basis within noninterest income. In addition, qualitative disclosures regarding noninterest income will be expanded. The Company will adopt this guidance on January 1, 2018 using the modified retrospective approach and does not expect the changes in presentation of certain contract costs or the expanded disclosures to have a significant impact on the Company's financial condition, results of operations, or liquidity. Amendments to Guidance on Classifying and Measuring Financial Instruments: In January of 2016, the FASB issued guidance that will require entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value. Any changes in fair value will be recognized in net income unless the investments qualify for a new practicability exception. This guidance also requires entities to adjust the fair value disclosures for financial instruments carried at amortized cost from an entry price to an exit price. No changes were made to the guidance for classifying and measuring investments in debt securities and loans. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Leases: In February of 2016, the FASB issued guidance to increase transparency and comparability across entities for leasing arrangements. This guidance requires lessees to recognize assets and liabilities for most leases. For lessors, this guidance modifies the lease classification criteria and the accounting for sales-type and direct financing leases. In addition, this guidance clarifies criteria for the determination of whether a contract is or contains a lease. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. During 2016, the Bank entered into a sale-leaseback transaction that resulted in a deferred gain of $82.5 million , with $74.6 million remaining as of December 31, 2017 . Upon adoption of this guidance, the remaining deferred gain will be recognized immediately as a cumulative-effect adjustment to equity and will no longer be accreted as a reduction to lease expense in net occupancy and equipment expense. For additional discussion of the sale-leaseback transaction, see note 8 " Premises, Furniture, and Equipment ." Management is evaluating the new guidance and the additional impact to the Company's financial condition, results of operations, or liquidity. Measurement of Credit Losses on Financial Instruments: In June of 2016, the FASB issued guidance that will require entities to present financial assets measured at amortized cost at the net amount expected to be collected, considering an entity's current estimate of all expected credit losses. In addition, credit losses relating to available-for-sale debt securities will be required to be recorded through an allowance for credit losses, with changes in credit loss estimates recognized through current earnings. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted, but not for periods beginning before December 15, 2018. Management is evaluating the new guidance and the impact to the Company's financial condition, results of operations, and liquidity. Classification of Certain Cash Receipts and Cash Payments: In August of 2016, the FASB issued guidance clarifying certain cash flow presentation and classification issues to reduce diversity in practice. This guidance is effective for annual and interim reporting periods beginning on or after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's Consolidated Statement of Cash Flows. Income Taxes: In October of 2016, the FASB issued guidance that requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Clarifying the Definition of a Business: In January of 2017, the FASB issued guidance that clarifies the definition of a business to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Accounting for Goodwill Impairment: In January of 2017, the FASB issued guidance that simplifies the accounting for goodwill impairment for all entities. The new guidance eliminates the requirement to calculate the implied fair value of goodwill using the second step of the quantitative two-step goodwill impairment model prescribed under current accounting guidance. Under the new guidance, if a reporting unit's carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. This guidance is effective for annual and interim goodwill impairment testing dates beginning after December 15, 2019. Early adoption is permitted for annual and interim goodwill impairment testing dates after January 1, 2017. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Presentation of Defined Benefit Retirement Plan Costs: In March of 2017, the FASB issued guidance that changes how employers that sponsor defined pension and or other postretirement benefit plans present the net periodic benefit cost in the income statement. Employers will present the service cost component of net periodic benefit cost in the same income statement line item as other employee compensation costs arising from services rendered during the period. Other components of net periodic benefit cost will be presented separately from the line item(s) that includes the service cost. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Premium Amortization on Purchased Callable Debt Securities: In March of 2017, the FASB issued guidance that shortens the amortization period for the premium on certain purchased callable debt securities to the earliest call date. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Share-based Payment Award Modifications: In May of 2017, the FASB issued guidance to reduce diversity in practice by clarifying when changes to the terms or conditions of a share-based payment award must be accounted for as a modification. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Derivatives and Hedging: In August of 2017, the FASB issued guidance to better align the financial reporting related to hedging activities with the economic objectives of those activities and to simplify the application of current hedge accounting guidance. Entities are required to apply the guidance using a modified retrospective method as of the period of adoption. This guidance is effective for annual and interim periods beginning after December 31, 2018. Early adoption is permitted. Management is evaluating the new guidance, but does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income: In February of 2018, the FASB issued guidance that requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 . Entities electing the reclassification are required to apply the guidance either at the beginning of the period of adoption or retrospectively for all periods impacted. This guidance is effective for annual and interim periods beginning after December 31, 2018. Early adoption is permitted. The Company has elected to reclassify $6.9 million of these stranded tax effects from accumulated other comprehensive loss to retained earnings as of the beginning of the period of adoption on January 1, 2018.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisitions	ACQUISITIONS Completed Acquisitions Standard Bancshares, Inc. On January 6, 2017, the Company completed its acquisition of Standard Bancshares, Inc. ("Standard") the holding company for Standard Bank and Trust Company. Pursuant to the terms of the merger agreement, on January 6, 2017, each outstanding share of Standard common stock was canceled and converted into the right to receive 0.4350 of a share of Company common stock. Based on the closing price of a share of Company common stock of $25.34 on that date, as reported by NASDAQ, the value of the merger consideration per share of Standard common stock was $11.02 . Each outstanding Standard stock settled right was redeemed for cash, and each outstanding Standard stock option and each share of Standard phantom stock was canceled and terminated in exchange for the right to receive cash, in each case, pursuant to the terms of the merger agreement. This resulted in an overall transaction value of approximately $580.7 million , which consisted of 21,057,085 shares of Company common stock and $47.1 million in cash. Goodwill of $345.3 million associated with the acquisition was recorded by the Company. All operating systems were converted during the first quarter of 2017. During 2017, the Company finalized the fair value adjustments associated with the Standard transaction, which required a measurement period adjustment of $6.0 million to increase goodwill. This adjustment was recognized in the current period in accordance with accounting guidance applicable to business combinations. Premier Asset Management LLC On February 28, 2017, the Company completed its acquisition of Premier, a registered investment advisor based in Chicago, Illinois. At the close of the acquisition, the Company acquired approximately $550.0 million of trust assets under management. The fair value adjustments, including goodwill, associated with this transaction remain preliminary and may change as the Company continues to finalize the fair value of the assets and liabilities acquired. NI Bancshares Corporation On March 8, 2016 , the Company completed its acquisition of NI Bancshares Corporation ("NI Bancshares"), the holding company for The National Bank & Trust Company of Sycamore, which included ten banking offices in northern Illinois and over $700.0 million in trust assets under management. The merger consideration was a combination of Company common stock and cash, at a purchase price of $70.1 million . Goodwill of $22.2 million associated with the acquisition was recorded by the Company. During 2017, the Company finalized the fair value adjustments associated with the NI Bancshares transaction, which required a measurement period adjustment of $423,000 to increase goodwill. This adjustment was recognized in the current period in accordance with accounting guidance applicable to business combinations. The following table presents the assets acquired and liabilities assumed, net of the fair value adjustments, in the Standard and NI Bancshares transactions as of the acquisition date. The assets acquired and liabilities assumed, both intangible and tangible, were recorded at their estimated fair values as of the acquisition date and have been accounted for under the acquisition method of accounting. Acquisition Activity (Dollar amounts in thousands, except share and per share data) Standard NI Bancshares January 6, 2017 March 8, 2016 Assets Cash and due from banks and interest-bearing deposits in other banks $ 102,149 $ 72,533 Securities available-for-sale 214,107 125,843 Securities held-to-maturity — 1,864 FHLB and FRB stock 3,247 1,549 Loans 1,762,303 396,181 OREO 8,424 2,863 Investment in BOLI 55,629 8,384 Goodwill 345,334 22,174 Other intangible assets 31,072 10,408 Premises, furniture, and equipment 56,517 19,636 Accrued interest receivable and other assets 60,278 16,453 Total assets $ 2,639,060 $ 677,888 Liabilities Noninterest-bearing deposits $ 675,354 $ 130,909 Interest-bearing deposits 1,348,520 464,012 Total deposits 2,023,874 594,921 Borrowed funds — 2,416 Intangible liabilities — 230 Accrued interest payable and other liabilities 34,471 10,239 Total liabilities 2,058,345 607,806 Consideration Paid Common stock (2017 - 21,057,085 share issued at $25.34 per share, 2016 - 3,042,494 shares issued at $18.059 per share), net of issuance costs 533,590 54,896 Cash paid 47,125 15,186 Total consideration paid 580,715 70,082 $ 2,639,060 $ 677,888 Expenses related to the acquisition and integration of completed and pending transactions totaled $20.1 million , $14.4 million and $1.4 million during the years ended December 31, 2017 , 2016 and 2015 , respectively, and are reported as a separate component within noninterest expense in the Consolidated Statements of Income. The acquisition of Standard was considered material to the Company's financial statements; therefore, pro forma financial data and related disclosures are included in the following tables. The unaudited pro forma combined results of operations for the years ended December 31, 2017 and 2016 are presented as if the Standard acquisition had occurred on January 1, 2016, the first day of the Company's 2016 fiscal year. The unaudited pro forma combined results of operations are presented for illustrative purposes only and do not necessarily indicate the financial results of the combined companies had the companies actually been combined at the beginning of the period presented. The unaudited pro forma combined results of operations also does not consider any potential impacts of potential revenue enhancements, anticipated cost savings and expense efficiencies, or asset dispositions, among other factors. Acquisition and integration related expenses directly attributable to the Standard acquisition have been excluded from the following table and were $19.1 million and $8.0 million for the years ended December 31, 2017 and 2016. Unaudited Pro Forma Combined Results of Operations (Dollar amounts in thousands) Years Ended December 31, 2017 2016 Total revenues (1) $ 636,762 $ 616,922 Net income 109,195 108,770 (1) Includes net interest income and total noninterest income. Acquired loans are recorded at fair value, which incorporates credit risk, at the date of acquisition. No allowance for credit losses is recorded on the acquisition date. Acquired loans are separated into (i) non-PCI and (ii) PCI loans. Non-PCI loans include loans that did not have evidence of credit deterioration since origination at the acquisition date. PCI loans include loans that had evidence of credit deterioration since origination and for which it was probable at acquisition that the Company would not collect all contractually required principal and interest payments. PCI loans are accounted for based on estimates of expected future cash flows. Accretable yield is recorded as interest income over the life of the loans if the timing and amount of the expected future cash flows can be reasonably estimated. The non-accretable yield represents the difference between contractually required payments and the expected future cash flows determined at acquisition. For additional discussion regarding significant accounting policies on acquired loans see Note 1, "Summary of Significant Accounting Policies." The following table presents additional detail for loans acquired in the Standard transaction at the acquisition date. Standard Acquired Loans (Dollar amounts in thousands) January 6, 2017 PCI Loans Non-PCI Loans Fair value $ 125,382 $ 1,636,921 Contractually required principal and interest payments 218,680 1,930,311 Best estimate of contractual cash flows not expected to be collected (1) 65,610 100,469 Best estimate of contractual cash flows expected to be collected 153,070 1,829,842 (1) Includes interest payments not expected to be collected due to loan prepayments as well as principal and interest payments not expected to be collected due to customer default.

Securities

Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Securities	SECURITIES A summary of the Company's securities portfolio by category and maturity is presented in the following tables. Securities Portfolio (Dollar amounts in thousands) As of December 31, 2017 2016 Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Fair Gains Losses Gains Losses Securities Available-for-Sale U.S. treasury securities $ 46,529 $ — $ (184 ) $ 46,345 $ 48,581 $ 26 $ (66 ) $ 48,541 U.S. agency securities 157,636 197 (986 ) 156,847 183,528 519 (410 ) 183,637 Collateralized mortgage 1,113,019 121 (17,954 ) 1,095,186 1,064,130 969 (17,653 ) 1,047,446 Other mortgage-backed 373,676 201 (4,334 ) 369,543 337,139 1,395 (5,879 ) 332,655 Municipal securities 209,558 693 (1,260 ) 208,991 273,319 1,245 (3,718 ) 270,846 Trust-preferred collateralized debt obligations ("CDOs") — — — — 47,681 261 (14,682 ) 33,260 Equity securities 7,408 194 (305 ) 7,297 3,206 147 (288 ) 3,065 Total securities available-for-sale $ 1,907,826 $ 1,406 $ (25,023 ) $ 1,884,209 $ 1,957,584 $ 4,562 $ (42,696 ) $ 1,919,450 Securities Held-to-Maturity Municipal securities $ 13,760 $ — $ (1,747 ) $ 12,013 $ 22,291 $ — $ (4,079 ) $ 18,212 Trading Securities $ 20,447 $ 17,920 Remaining Contractual Maturity of Securities (Dollar amounts in thousands) As of December 31, 2017 Available-for-Sale Held-to-Maturity Amortized Cost Fair Value Amortized Cost Fair Value One year or less $ 87,379 $ 87,053 $ 1,432 $ 1,250 After one year to five years 323,203 322,000 5,831 5,090 After five years to ten years 3,141 3,130 2,243 1,959 After ten years — — 4,254 3,714 Securities that do not have a single contractual maturity date 1,494,103 1,472,026 — — Total $ 1,907,826 $ 1,884,209 $ 13,760 $ 12,013 The carrying value of securities available-for-sale that were pledged to secure deposits or for other purposes as permitted or required by law totaled $1.1 billion for both December 31, 2017 and 2016 . No securities held-to-maturity were pledged as of December 31, 2017 or 2016 . Excluding securities issued or backed by the U.S. government and its agencies and U.S. government-sponsored enterprises, there were no investments in securities from one issuer that exceeded 10% of total stockholders' equity as of December 31, 2017 or 2016 . During the years ended December 31, 2017 , 2016 , and 2015 there were no material gross trading gains (losses). The following table presents net realized (losses) gains on securities available-for-sale for the three years ended December 31, 2017 . Securities Available-for-Sale (Losses) Gains (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Gains (losses) on sales of securities: Gross realized gains $ 5,478 $ 1,589 $ 2,519 Gross realized losses (7,354 ) (169 ) (146 ) Net realized (losses) gains on sales of securities (1,876 ) 1,420 2,373 Non-cash impairment charges: OTTI — — — Net realized (losses) gains $ (1,876 ) $ 1,420 $ 2,373 Net securities losses for 2017 consisted primarily of sales of CMOs and CDOs at net losses of $2.8 million and $404,000 , respectively, partially off-set by sales of municipal and other securities at gains of $854,000 and $449,000 , respectively. During 2016, net securities gains consisted primarily of sales of municipal securities at net gains of $1.1 million and equity securities at net gains of $304,000 . Net securities gains for 2015 consisted primarily of sales of MBSs at net gains of $1.9 million and sales of CMOs, municipal securities, and other investments at net gains of $521,000 . Accounting guidance requires that the credit portion of an OTTI charge be recognized through income. If a decline in fair value below carrying value is not attributable to credit deterioration and the Company does not intend to sell the security or believe it would not be more likely than not required to sell the security prior to recovery, the Company records the non-credit related portion of the decline in fair value in other comprehensive income (loss) . The following table presents a rollforward of life-to-date OTTI recognized in earnings related to all securities available-for-sale held by the Company for the years ended December 31, 2017 , 2016 , and 2015 . Changes in OTTI Recognized in Earnings (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 23,345 $ 23,345 $ 23,516 OTTI included in earnings (1) : Losses on securities that previously had OTTI — — — Losses on securities that did not previously have OTTI — — — Reduction for securities sales (2) (23,345 ) — (171 ) Ending balance $ — $ 23,345 $ 23,345 (1) Included in net securities (losses) gains in the Consolidated Statements of Income. (2) These reductions were driven by the sale of 11 CDOs with a carrying value of $47.7 million during the year ended December 31, 2017 and one CMO with a carrying value of $1.3 million during the year ended December 31, 2015. The following table presents the aggregate amount of unrealized losses and the aggregate related fair values of securities with unrealized losses as of December 31, 2017 and 2016 . Securities in an Unrealized Loss Position (Dollar amounts in thousands) Less Than 12 Months Greater Than 12 Months Total Number of Securities Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses As of December 31, 2017 Securities Available-for-Sale U.S. treasury securities 20 $ 19,918 $ 87 $ 26,427 $ 97 $ 46,345 $ 184 U.S. agency securities 72 66,899 300 58,021 686 124,920 986 CMOs 211 365,131 3,265 633,227 14,689 998,358 17,954 MBSs 86 126,136 902 210,017 3,432 336,153 4,334 Municipal securities 265 35,500 479 81,360 781 116,860 1,260 Equity securities 2 391 214 6,386 91 6,777 305 Total 656 $ 613,975 $ 5,247 $ 1,015,438 $ 19,776 $ 1,629,413 $ 25,023 Securities Held-to-Maturity Municipal securities 8 $ — $ — $ 12,013 $ 1,747 $ 12,013 $ 1,747 As of December 31, 2016 Securities Available-for-Sale U.S. treasury securities 16 $ 33,505 $ 61 $ 3,995 $ 5 $ 37,500 $ 66 U.S. agency securities 28 62,064 364 11,814 46 73,878 410 CMOs 194 523,233 10,309 411,758 7,344 934,991 17,653 MBSs 68 221,174 4,726 77,780 1,154 298,954 5,880 Municipal securities 380 133,957 3,059 29,280 659 163,237 3,718 CDOs 7 — — 30,592 14,682 30,592 14,682 Equity securities 2 404 201 2,319 86 2,723 287 Total 695 $ 974,337 $ 18,720 $ 567,538 $ 23,976 $ 1,541,875 $ 42,696 Securities Held-to-Maturity Municipal securities 14 $ — $ — $ 18,212 $ 4,079 $ 18,212 $ 4,079 Substantially all of the Company's CMOs and other MBSs are either backed by U.S. government-owned agencies or issued by U.S. government-sponsored enterprises. Municipal securities are issued by municipal authorities, and the majority are supported by third-party insurance or some other form of credit enhancement. Management does not believe any of these securities with unrealized losses as of December 31, 2017 represent OTTI related to credit deterioration. These unrealized losses are attributed to changes in interest rates and temporary market movements. The Company does not intend to sell these securities and it is not more likely than not that the Company will be required to sell them before recovery of their amortized cost basis, which may be at maturity.

Loans

Loans	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loans	LOANS Loans Held-for-Investment The following table presents the Company's loans held-for-investment by class. Loan Portfolio (Dollar amounts in thousands) As of December 31, 2017 2016 Commercial and industrial $ 3,529,914 $ 2,827,658 Agricultural 430,886 389,496 Commercial real estate: Office, retail, and industrial 1,979,820 1,581,967 Multi-family 675,463 614,052 Construction 539,820 451,540 Other commercial real estate 1,358,515 979,528 Total commercial real estate 4,553,618 3,627,087 Total corporate loans 8,514,418 6,844,241 Home equity 827,055 747,983 1-4 family mortgages 774,357 423,922 Installment 321,982 237,999 Total consumer loans 1,923,394 1,409,904 Total loans $ 10,437,812 $ 8,254,145 Deferred loan fees included in total loans $ 4,986 $ 3,838 Overdrawn demand deposits included in total loans 8,587 7,836 The Company primarily lends to community-based and mid-sized businesses, commercial real estate customers, and consumers in its markets. Within these areas, the Company diversifies its loan portfolio by loan type, industry, and borrower. Commercial and industrial loans are underwritten after evaluating and understanding the borrower's ability to operate its business. As part of the underwriting process, the Company examines current and expected future cash flows to determine the ability of the borrower to repay its obligation. Commercial and industrial loans are primarily made based on the identified cash flows of the borrower and secondarily on the underlying collateral provided by the borrower. The cash flows of the borrower may not be as expected, and the collateral securing these loans may fluctuate in value due to economic or other factors. Most commercial and industrial loans are secured by the assets being financed or other business assets, such as accounts receivable or inventory, and may incorporate a personal guarantee. In the case of loans secured by accounts receivable, the availability of funds for the repayment of these loans substantially depend on the ability of the borrower to collect amounts due from its customers. Some short-term loans may be made on an unsecured basis. Agricultural loans are generally provided to meet seasonal production, equipment, and farm real estate borrowing needs of individual and corporate crop and livestock producers. As part of the underwriting process, the Company examines projected future cash flows, financial statement stability, and the value of the underlying collateral. Seasonal crop production loans are repaid by the liquidation of the financed crop that is typically covered by crop insurance. Equipment and real estate term loans are repaid through cash flows of the farming operation. Commercial real estate loans are subject to underwriting standards and processes similar to commercial and industrial loans. The repayment of commercial real estate loans depends on the successful operation of the property securing the loan or the business conducted on the property securing the loan. This category of loans may be more adversely affected by conditions in the real estate market. Management monitors and evaluates commercial real estate loans based on cash flow, collateral, geography, and risk rating criteria. The mix of properties securing the loans in our commercial real estate portfolio are balanced between owner-occupied and investor categories and is diverse in terms of type and geographic location, generally within the Company's markets. Construction loans are generally made based on estimates of costs and values associated with the completed project and are underwritten utilizing feasibility studies, independent appraisal reviews, sensitivity analyses of absorption and lease rates, and financial analyses of the developers and property owners. Sources of repayment may be permanent loans from long-term lenders, sales of developed property, or an interim loan commitment until permanent financing is obtained. Generally, construction loans have a higher risk profile than other real estate loans since repayment is impacted by real estate values, interest rate changes, governmental regulation of real property, demand and supply of alternative real estate, the availability of long-term financing, and changes in general economic conditions. Consumer loans are centrally underwritten using a credit scoring model developed by the Fair Isaac Corporation ("FICO"), which employs a risk-based system to determine the probability that a borrower may default. Underwriting standards for home equity loans are heavily influenced by statutory requirements, which include loan-to-value and affordability ratios, risk-based pricing strategies, and documentation requirements. The home equity category consists mainly of revolving lines of credit secured by junior liens on owner-occupied real estate. Loan-to-value ratios on home equity loans and 1-4 family mortgages are based on the current appraised value of the collateral. Repayment for these loans is dependent on the borrower's continued financial stability, and is more likely to be impacted by adverse personal circumstances. The Bank is a member of the FHLB and FRB and has access to financing secured by designated assets that may include qualifying commercial real estate, residential and multi-family mortgages, home equity loans, and certain municipal and mortgage-backed securities. The carrying value of loans that were pledged to secure liabilities as of December 31, 2017 and 2016 are presented below. Carrying Value of Loans Pledged (Dollar amounts in thousands) As of December 31 2017 2016 Loans pledged to secure: FHLB advances (blanket pledge) $ 4,587,240 $ 3,667,202 FRB's Discount Window Primary Credit Program 1,099,712 777,950 Total $ 5,686,952 $ 4,445,152 As of December 31, 2017 and 2016 , based on loans pledged under a blanket pledge agreement noted in the table above, the Bank was eligible to borrow up to $2.6 billion and $2.0 billion , respectively, in FHLB advances. As of December 31, 2017 and 2016 , the Bank was eligible to borrow up to $843.6 million and $629.7 million , respectively, through the FRB's Discount Window Primary Credit Program based on assets pledged. For additional disclosure related to the Company's outstanding balance of borrowings, see Note 11 , " Borrowed Funds ." Loan Sales The following table presents loan sales for the years ended December 31, 2017 , 2016 , and 2015 . Loan Sales (Dollar amounts in thousands) As of December 31, 2017 2016 2015 Corporate loan sales Proceeds from sales $ 52,974 $ 54,681 $ 31,091 Less book value of loans sold 51,781 52,821 29,535 Net gains on corporate sales (1) $ 1,193 $ 1,860 $ 1,556 1-4 family mortgage loan sales Proceeds from sales $ 258,626 $ 290,383 $ 185,308 Less book value of loans sold 252,741 283,312 180,017 Net gains on 1-4 family mortgage sales (2) 5,885 7,071 5,291 Total net gains on loan sales $ 7,078 $ 8,931 $ 6,847 (1) Net gains on corporate loan sales are included in other service charges, commissions, and fees in the Consolidated Statements of Income. (2) Net gains on mortgage loan sales are included in mortgage banking income in the Consolidated Statements of Income. The Company retained servicing responsibilities for a portion of the 1-4 family mortgage loans sold and collects servicing fees equal to a percentage of the outstanding principal balance. For additional disclosure related to the Company's obligations resulting from the sale of certain 1-4 family mortgage loans, see Note 20 , " Commitments, Guarantees, and Contingent Liabilities ."

Acquired and Covered Loans

Acquired and Covered Loans	12 Months Ended
	Dec. 31, 2017
Acquired Loans [Abstract]
Acquired and Covered Loans	ACQUIRED AND COVERED LOANS Covered loans consist of loans acquired by the Company in FDIC-assisted transactions which are covered by the FDIC Agreements. Acquired loans consist of all other loans that were acquired in business combinations that are not covered by the FDIC Agreements. Both acquired and covered loans are included in loans in the Consolidated Statements of Financial Condition. The significant accounting policies related to acquired and covered loans, which are classified as PCI and Non-PCI, and the related FDIC indemnification asset, are presented in Note 1 , " Summary of Significant Accounting Policies ." Non-residential mortgage loans related to FDIC-assisted transactions are no longer covered under the FDIC Agreements. These non-residential loans, which totaled $12.7 million and $14.9 million as of December 31, 2017 and 2016 , respectively, are included in acquired loans and no longer classified as covered loans. The losses on residential mortgage loans will continue to be covered under the FDIC Agreements through various dates between December 31, 2019 and September 30, 2020. The following table presents acquired and covered PCI and Non-PCI loans as of December 31, 2017 and 2016 . Acquired and Covered Loans (Dollar amounts in thousands) As of December 31, 2017 2016 PCI Non-PCI Total PCI Non-PCI Total Acquired loans $ 130,694 $ 1,512,664 $ 1,643,358 $ 53,772 $ 613,339 $ 667,111 Covered loans 6,759 11,789 18,548 7,895 15,379 23,274 Total acquired and covered loans $ 137,453 $ 1,524,453 $ 1,661,906 $ 61,667 $ 628,718 $ 690,385 The outstanding balance of PCI loans was $210.7 million and $84.8 million as of December 31, 2017 and 2016 , respectively. Acquired non-PCI loans that are renewed are no longer classified as acquired loans. These loans totaled $366.0 million and $117.6 million as of December 31, 2017 and 2016 , respectively. In connection with the FDIC Agreements, the Company recorded an indemnification asset. To maintain eligibility for the loss share reimbursement, the Company is required to follow certain servicing procedures as specified in the FDIC Agreements. The Company was in compliance with those requirements as of December 31, 2017 , 2016 , and 2015 . A rollforward of the carrying value of the FDIC indemnification asset for the three years ended December 31, 2017 is presented in the following table. Changes in the FDIC Indemnification Asset (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 4,522 $ 3,903 $ 8,452 Amortization (1,208 ) (1,185 ) (1,461 ) Change in expected reimbursements from the FDIC for changes in expected credit losses (792 ) 330 1,313 Net payments to (from) the FDIC 792 1,474 (4,401 ) Ending balance $ 3,314 $ 4,522 $ 3,903 Changes in the accretable yield for acquired and covered PCI loans were as follows. Changes in Accretable Yield (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 19,386 $ 24,912 $ 28,244 Additions 27,316 3,981 1,168 Accretion (15,529 ) (8,063 ) (11,311 ) Other (1) 1,784 (1,444 ) 6,811 Ending balance $ 32,957 $ 19,386 $ 24,912 (1) Increases represent a rise in the expected future cash flows to be collected over the remaining estimated life of the underlying portfolio while decreases result from the resolution of certain loans occurring earlier than anticipated. Total accretion on acquired and covered PCI and non-PCI loans for December 31, 2017 , 2016 , and 2015 was $33.9 million , $14.6 million , and $16.3 million , respectively.

Past Due Loans, Allowance For C

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs	12 Months Ended
	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs	PAST DUE LOANS, ALLOWANCE FOR CREDIT LOSSES, IMPAIRED LOANS, AND TDRS Past Due and Non-accrual Loans The following table presents an aging analysis of the Company's past due loans as of December 31, 2017 and 2016 . The aging is determined without regard to accrual status. The table also presents non-performing loans, consisting of non-accrual loans (the majority of which are past due) and loans 90 days or more past due and still accruing interest, as of each balance sheet date. Aging Analysis of Past Due Loans and Non-Performing Loans by Class (Dollar amounts in thousands) Aging Analysis (Accruing and Non-accrual) Non-performing Loans Current (1) 30-89 Days Past Due 90 Days or More Past Due Total Past Due Total Loans Non-accrual (2) 90 Days or More Past Due, Still Accruing Interest As of December 31, 2017 Commercial and industrial $ 3,490,783 $ 34,620 $ 4,511 $ 39,131 $ 3,529,914 $ 40,580 $ 1,830 Agricultural 430,221 280 385 665 430,886 219 177 Commercial real estate: Office, retail, and industrial 1,970,564 3,156 6,100 9,256 1,979,820 11,560 345 Multi-family 672,098 3,117 248 3,365 675,463 377 20 Construction 539,043 198 579 777 539,820 209 371 Other commercial real estate 1,353,263 2,545 2,707 5,252 1,358,515 3,621 317 Total commercial real estate 4,534,968 9,016 9,634 18,650 4,553,618 15,767 1,053 Total corporate loans 8,455,972 43,916 14,530 58,446 8,514,418 56,566 3,060 Home equity 820,099 4,102 2,854 6,956 827,055 5,946 98 1-4 family mortgages 770,120 2,145 2,092 4,237 774,357 4,412 — Installment 319,178 2,407 397 2,804 321,982 — 397 Total consumer loans 1,909,397 8,654 5,343 13,997 1,923,394 10,358 495 Total loans $ 10,365,369 $ 52,570 $ 19,873 $ 72,443 $ 10,437,812 $ 66,924 $ 3,555 As of December 31, 2016 Commercial and industrial $ 2,816,442 $ 6,426 $ 4,790 $ 11,216 $ 2,827,658 $ 29,938 $ 374 Agricultural 388,596 — 900 900 389,496 181 736 Commercial real estate: Office, retail, and industrial 1,564,007 5,327 12,633 17,960 1,581,967 17,277 1,129 Multi-family 612,446 858 748 1,606 614,052 311 604 Construction 450,927 332 281 613 451,540 286 — Other commercial real estate 974,575 1,307 3,646 4,953 979,528 2,892 1,526 Total commercial real estate 3,601,955 7,824 17,308 25,132 3,627,087 20,766 3,259 Total corporate loans 6,806,993 14,250 22,998 37,248 6,844,241 50,885 4,369 Home equity 740,919 4,545 2,519 7,064 747,983 5,465 109 1-4 family mortgages 420,264 2,652 1,006 3,658 423,922 2,939 272 Installment 236,264 1,476 259 1,735 237,999 — 259 Total consumer loans 1,397,447 8,673 3,784 12,457 1,409,904 8,404 640 Total loans $ 8,204,440 $ 22,923 $ 26,782 $ 49,705 $ 8,254,145 $ 59,289 $ 5,009 (1) PCI loans with an accretable yield are considered current. (2) Includes PCI loans of $763,000 and $681,000 as of December 31, 2017 and December 31, 2016 , respectively, which no longer have an accretable yield as estimates of expected future cash flows have decreased since the acquisition due to credit deterioration. Allowance for Credit Losses The Company maintains an allowance for credit losses at a level deemed adequate by management to absorb estimated losses inherent in the existing loan portfolio. See Note 1 , " Summary of Significant Accounting Policies ," for the accounting policy for the allowance for credit losses. A rollforward of the allowance for credit losses by portfolio segment for the years ended December 31, 2017 , 2016 , and 2015 is presented in the table below. Allowance for Credit Losses by Portfolio Segment (Dollar amounts in thousands) Commercial, Industrial, and Agricultural Office, Retail, and Industrial Multi-family Construction Other Commercial Real Estate Consumer Reserve for Unfunded Commitments Total Allowance for Credit Losses Year Ended December 31, 2017 Beginning balance $ 40,709 $ 17,595 $ 3,261 $ 3,444 $ 7,739 $ 13,335 $ 1,000 $ 87,083 Charge-offs (22,885 ) (190 ) — (38 ) (755 ) (6,955 ) — (30,823 ) Recoveries 4,150 2,935 39 270 244 1,541 — 9,179 Net charge-offs (18,735 ) 2,745 39 232 (511 ) (5,414 ) — (21,644 ) Provision for loan 33,817 (9,344 ) (766 ) (195 ) (847 ) 8,625 — 31,290 Ending Balance $ 55,791 $ 10,996 $ 2,534 $ 3,481 $ 6,381 $ 16,546 $ 1,000 $ 96,729 Year Ended December 31, 2016 Beginning balance $ 37,074 $ 13,124 $ 2,469 $ 1,440 $ 6,109 $ 13,414 $ 1,225 $ 74,855 Charge-offs (9,982 ) (4,707 ) (307 ) (134 ) (2,932 ) (5,231 ) — (23,293 ) Recoveries 2,451 337 97 56 524 1,298 — 4,763 Net charge-offs (7,531 ) (4,370 ) (210 ) (78 ) (2,408 ) (3,933 ) — (18,530 ) Provision for loan losses and other 11,166 8,841 1,002 2,082 4,038 3,854 (225 ) 30,758 Ending balance $ 40,709 $ 17,595 $ 3,261 $ 3,444 $ 7,739 $ 13,335 $ 1,000 $ 87,083 Year Ended December 31, 2015 Beginning balance $ 31,177 $ 13,053 $ 2,387 $ 3,031 $ 9,019 $ 14,027 $ 1,816 $ 74,510 Charge-offs (16,422 ) (2,899 ) (568 ) (139 ) (2,678 ) (4,211 ) — (26,917 ) Recoveries 2,588 534 15 350 2,031 1,183 — 6,701 Net charge-offs (13,834 ) (2,365 ) (553 ) 211 (647 ) (3,028 ) — (20,216 ) Provision for loan 19,731 2,436 635 (1,802 ) (2,263 ) 2,415 (591 ) 20,561 Ending balance $ 37,074 $ 13,124 $ 2,469 $ 1,440 $ 6,109 $ 13,414 $ 1,225 $ 74,855 The table below provides a breakdown of loans and the related allowance for credit losses by portfolio segment as of December 31, 2017 and 2016 . Loans and Related Allowance for Credit Losses by Portfolio Segment (Dollar amounts in thousands) Loans Allowance for Credit Losses Individually Evaluated for Impairment Collectively Evaluated for Impairment PCI Total Individually Evaluated for Impairment Collectively Evaluated for Impairment PCI Total As of December 31, 2017 Commercial, industrial, and $ 38,718 $ 3,909,380 $ 12,702 $ 3,960,800 $ 10,074 $ 45,293 $ 424 $ 55,791 Commercial real estate: Office, retail, and industrial 10,810 1,954,435 14,575 1,979,820 — 9,333 1,663 10,996 Multi-family 621 660,771 14,071 675,463 — 2,436 98 2,534 Construction — 530,977 8,843 539,820 — 3,331 150 3,481 Other commercial real estate 1,468 1,291,723 65,324 1,358,515 — 5,415 966 6,381 Total commercial real estate 12,899 4,437,906 102,813 4,553,618 — 20,515 2,877 23,392 Total corporate loans 51,617 8,347,286 115,515 8,514,418 10,074 65,808 3,301 79,183 Consumer — 1,901,456 21,938 1,923,394 — 15,533 1,013 16,546 Reserve for unfunded — — — — — 1,000 — 1,000 Total loans $ 51,617 $ 10,248,742 $ 137,453 $ 10,437,812 $ 10,074 $ 82,341 $ 4,314 $ 96,729 As of December 31, 2016 Commercial, industrial, and $ 24,645 $ 3,189,327 $ 3,182 $ 3,217,154 $ 507 $ 39,554 $ 648 $ 40,709 Commercial real estate: Office, retail, and industrial 16,287 1,553,234 12,446 1,581,967 — 16,148 1,447 17,595 Multi-family 398 601,429 12,225 614,052 — 3,059 202 3,261 Construction 34 447,058 4,448 451,540 — 3,280 164 3,444 Other commercial real estate 1,286 965,900 12,342 979,528 18 6,613 1,108 7,739 Total commercial real estate 18,005 3,567,621 41,461 3,627,087 18 29,100 2,921 32,039 Total corporate loans 42,650 6,756,948 44,643 6,844,241 525 68,654 3,569 72,748 Consumer — 1,392,880 17,024 1,409,904 — 12,210 1,125 13,335 Reserve for unfunded — — — — — 1,000 — 1,000 Total loans $ 42,650 $ 8,149,828 $ 61,667 $ 8,254,145 $ 525 $ 81,864 $ 4,694 $ 87,083 Loans Individually Evaluated for Impairment The following table presents loans individually evaluated for impairment by class of loan as of December 31, 2017 and 2016 . PCI loans are excluded from this disclosure. Impaired Loans Individually Evaluated by Class (Dollar amounts in thousands) As of December 31, 2017 2016 Recorded Investment In Recorded Investment In Loans with No Specific Reserve Loans with a Specific Reserve Unpaid Principal Balance Specific Reserve Loans with No Specific Reserve Loans with a Specific Reserve Unpaid Principal Balance Specific Reserve Commercial and industrial $ 4,234 $ 34,484 $ 53,192 $ 10,074 $ 11,579 $ 13,066 $ 29,514 $ 507 Agricultural — — — — — — — — Commercial real estate: Office, retail, and industrial 7,154 3,656 14,246 — 16,287 — 21,057 — Multi-family 621 — 621 — 398 — 398 — Construction — — — — 34 — 34 — Other commercial real estate 1,468 — 1,566 — 1,016 270 2,141 18 Total commercial real estate 9,243 3,656 16,433 — 17,735 270 23,630 18 Total impaired loans $ 13,477 $ 38,140 $ 69,625 $ 10,074 $ 29,314 $ 13,336 $ 53,144 $ 525 The following table presents the average recorded investment and interest income recognized on impaired loans by class for the years ended December 31, 2017 , 2016 , and 2015 . PCI loans are excluded from this disclosure. Average Recorded Investment and Interest Income Recognized on Impaired Loans by Class (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Average Recorded Investment Interest Income Recognized (1) Average Recorded Investment Interest Income Recognized (1) Average Interest (1) Commercial and industrial $ 33,956 $ 1,059 $ 9,178 $ 104 $ 8,940 $ 163 Agricultural 279 101 — — — — Commercial real estate: Office, retail, and industrial 13,106 325 12,867 291 9,359 52 Multi-family 441 28 479 11 855 13 Construction 7 136 63 — 3,902 118 Other commercial real estate 1,615 41 2,809 86 3,310 44 Total commercial real estate 15,170 530 16,218 388 17,426 227 Total impaired loans $ 49,404 $ 1,690 $ 25,396 $ 492 $ 26,366 $ 390 (1) Recorded using the cash basis of accounting. Credit Quality Indicators Corporate loans and commitments are assessed for credit risk and assigned ratings based on various characteristics, such as the borrower's cash flow, leverage, and collateral. Ratings for commercial credits are reviewed periodically. The following tables present credit quality indicators by class for corporate and consumer loans as of December 31, 2017 and 2016 . Corporate Credit Quality Indicators by Class (Dollar amounts in thousands) Pass Special (1)(4) Substandard (2)(4) Non-accrual (3) Total As of December 31, 2017 Commercial and industrial $ 3,388,133 $ 70,863 $ 30,338 $ 40,580 $ 3,529,914 Agricultural 413,946 10,989 5,732 219 430,886 Commercial real estate: Office, retail, and industrial 1,903,737 25,546 38,977 11,560 1,979,820 Multi-family 665,496 7,395 2,195 377 675,463 Construction 521,911 10,184 7,516 209 539,820 Other commercial real estate 1,304,337 29,624 20,933 3,621 1,358,515 Total commercial real estate 4,395,481 72,749 69,621 15,767 4,553,618 Total corporate loans $ 8,197,560 $ 154,601 $ 105,691 $ 56,566 $ 8,514,418 As of December 31, 2016 Commercial and industrial $ 2,638,833 $ 92,340 $ 66,547 $ 29,938 $ 2,827,658 Agricultural 366,382 17,039 5,894 181 389,496 Commercial real estate: Office, retail, and industrial 1,491,170 34,007 39,513 17,277 1,581,967 Multi-family 607,342 4,370 2,029 311 614,052 Construction 438,946 111 12,197 286 451,540 Other commercial real estate 951,284 11,808 13,544 2,892 979,528 Total commercial real estate 3,488,742 50,296 67,283 20,766 3,627,087 Total corporate loans $ 6,493,957 $ 159,675 $ 139,724 $ 50,885 $ 6,844,241 (1) Loans categorized as special mention exhibit potential weaknesses that require the close attention of management since these potential weaknesses may result in the deterioration of repayment prospects in the future. (2) Loans categorized as substandard exhibit a well-defined weakness that may jeopardize the liquidation of the debt. These loans continue to accrue interest because they are well-secured and collection of principal and interest is expected within a reasonable time. (3) Loans categorized as non-accrual exhibit a well-defined weakness that may jeopardize the liquidation of the debt or result in a loss if the deficiencies are not corrected. (4) Total special mention and substandard loans includes accruing TDRs of $657,000 as of December 31, 2017 and $834,000 as of December 31, 2016 . Consumer Credit Quality Indicators by Class (Dollar amounts in thousands) Performing Non-accrual Total As of December 31, 2017 Home equity $ 821,109 $ 5,946 $ 827,055 1-4 family mortgages 769,945 4,412 774,357 Installment 321,982 — 321,982 Total consumer loans $ 1,913,036 $ 10,358 $ 1,923,394 As of December 31, 2016 Home equity $ 742,518 $ 5,465 $ 747,983 1-4 family mortgages 420,983 2,939 423,922 Installment 237,999 — 237,999 Total consumer loans $ 1,401,500 $ 8,404 $ 1,409,904 TDRs TDRs are generally performed at the request of the individual borrower and may include forgiveness of principal, reduction in interest rates, changes in payments, and maturity date extensions. The table below presents TDRs by class as of December 31, 2017 and 2016 . See Note 1 , " Summary of Significant Accounting Policies ," for the accounting policy for TDRs. TDRs by Class (Dollar amounts in thousands) As of December 31, 2017 2016 Accruing Non-accrual (1) Total Accruing Non-accrual (1) Total Commercial and industrial $ 264 $ 18,959 $ 19,223 $ 281 $ 150 $ 431 Agricultural — — — — — — Commercial real estate: Office, retail, and industrial — 4,236 4,236 155 4,733 4,888 Multi-family 574 149 723 586 168 754 Construction — — — — — — Other commercial real estate 192 — 192 268 48 316 Total commercial real estate 766 4,385 5,151 1,009 4,949 5,958 Total corporate loans 1,030 23,344 24,374 1,290 5,099 6,389 Home equity 86 738 824 177 820 997 1-4 family mortgages 680 451 1,131 824 378 1,202 Installment — — — — — — Total consumer loans 766 1,189 1,955 1,001 1,198 2,199 Total loans $ 1,796 $ 24,533 $ 26,329 $ 2,291 $ 6,297 $ 8,588 (1) These TDRs are included in non-accrual loans in the preceding tables. TDRs are included in the calculation of the allowance for credit losses in the same manner as impaired loans. There were $2.0 million in specific reserves related to TDRs as of December 31, 2017 , and there were no specific reserves related to TDRs as of December 31, 2016 . The following table presents a summary of loans that were restructured during the years ended December 31, 2017 , 2016 , and 2015 . Loans Restructured During the Period (Dollar amounts in thousands) Number of Loans Pre-Modification Recorded Investment Funds Disbursed Interest and Escrow Capitalized Charge-offs Post-Modification Recorded Investment Year Ended December 31, 2017 Commercial and industrial 12 $ 26,733 $ 9,035 $ — $ 6,232 $ 29,536 Office, retail, and industrial 2 3,656 — — — 3,656 Total loans restructured during the period 14 $ 30,389 $ 9,035 $ — $ 6,232 $ 33,192 Year Ended December 31, 2016 Office, retail, and industrial 1 $ 5,460 $ — $ — $ 1,083 $ 4,377 Other commercial real estate 1 745 — — — 745 Total loans restructured during the period 2 $ 6,205 $ — $ — $ 1,083 $ 5,122 Year Ended December 31, 2015 Home equity 1 $ 120 $ — $ — $ — $ 120 1-4 family mortgages 2 325 — — — 325 Total loans restructured during the period 3 $ 445 $ — $ — $ — $ 445 Accruing TDRs that do not perform in accordance with their modified terms are transferred to non-accrual. The following table presents TDRs that had payment defaults during the years ended December 31, 2017 , 2016 , and 2015 where the default occurred within twelve months of the restructure date. TDRs That Defaulted Within Twelve Months of the Restructured Date (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment Home equity — $ — 1 $ 119 — $ — Total — $ — 1 $ 119 — $ — A rollforward of the carrying value of TDRs for the years ended December 31, 2017 , 2016 , and 2015 is presented in the following table. TDR Rollforward (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Accruing Beginning balance $ 2,291 $ 2,743 $ 3,704 Additions 15,819 — 120 Net payments (1,923 ) (120 ) (774 ) Returned to performing status — — — Net transfers to non-accrual (14,391 ) (332 ) (307 ) Ending balance 1,796 2,291 2,743 Non-accrual Beginning balance 6,297 2,324 19,904 Additions 14,570 6,205 325 Net payments (4,380 ) (1,072 ) (15,525 ) Charge-offs (6,345 ) (1,492 ) (2,687 ) Transfers to OREO — — — Loans sold — — — Net transfers from accruing 14,391 332 307 Ending balance 24,533 6,297 2,324 Total TDRs $ 26,329 $ 8,588 $ 5,067 For TDRs to be removed from TDR status in the calendar year after the restructuring, the loans must (i) have an interest rate and terms that reflect market conditions at the time of restructuring, and (ii) be in compliance with the modified terms. Loans that were not restructured at market rates and terms, that are not in compliance with the modified terms, or for which there is a concern about the future ability of the borrower to meet its obligations under the modified terms, continue to be separately reported as restructured until paid in full or charged-off. There were no material commitments to lend additional funds to borrowers with TDRs as of December 31, 2017 and 2016 .

Premises, Furniture, and Equipm

Premises, Furniture, and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises, Furniture, and Equipment	PREMISES, FURNITURE, AND EQUIPMENT The following table summarizes the Company's premises, furniture, and equipment by category. Premises, Furniture, and Equipment (Dollar amounts in thousands) As of December 31, 2017 2016 Land $ 30,470 $ 18,304 Premises 123,873 94,369 Furniture and equipment 115,013 105,859 Total cost 269,356 218,532 Accumulated depreciation (148,248 ) (140,030 ) Net book value of premises, furniture, and equipment 121,108 78,502 Assets held-for-sale 2,208 4,075 Premises, furniture, and equipment, net $ 123,316 $ 82,577 During 2016, the Bank completed a sale-leaseback transaction, whereby the Bank sold to a third-party for an aggregate cash purchase price of $150.3 million , 55 properties with book values totaling $58.8 million , owned and operated by the Bank as branches. The Bank concurrently entered into triple net lease agreements with certain affiliates of the third-party for each of the branches sold. Subject to the right of the Bank to terminate certain of the lease agreements at the end of the eleventh year, the lease agreements have initial terms of 14 years. Each lease agreement provides the Bank with five consecutive renewal options of five years each. The sale-leaseback transaction resulted in a pre-tax gain of $88.0 million , net of transaction related expenses, of which $5.5 million was immediately recognized in earnings. Remaining pre-tax gains were $74.6 million and $81.0 million as of December 31, 2017 and 2016 , respectively, and will be accreted as a reduction to lease expense in net occupancy and equipment expense in the Consolidated Statement of Income on a straight-line basis over the initial terms of the leases. As of December 31, 2017 and 2016 , assets held-for-sale consisted of former branches that are no longer in operation and parcels of land previously purchased for expansion. Depreciation on premises, furniture, and equipment totaled $14.0 million in 2017 , $12.8 million in 2016 , and $13.4 million in 2015 . Operating Leases As of December 31, 2017 , the Company was obligated to utilize certain premises and equipment under certain non-cancelable operating leases, which expire at various dates through the year ending December 31, 2033 . Many of these leases contain renewal options and certain leases provide options to purchase the leased property during or at the expiration of the lease period at specific prices. Some leases contain escalation clauses calling for rentals to be adjusted for increased real estate taxes and other operating expenses or proportionately adjusted for increases in consumer or other price indices. The following summary reflects the future minimum payments by year required under operating leases that have initial or remaining non-cancelable lease terms in excess of one year as of December 31, 2017 . Future Minimum Operating Lease Payments (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 19,241 2019 17,659 2020 16,926 2021 16,732 2022 16,464 2023 and thereafter 119,847 Total minimum lease payments $ 206,869 The Company assumed certain operating leases related to various branches in previous acquisitions. An intangible liability is recorded when the cash flows of a lease exceed its fair market value. This intangible liability is accreted into income as a reduction to net occupancy and equipment expense using the straight-line method over the initial term of each lease, which expire between 2018 and 2030. The intangible liability is included in accrued interest and other liabilities in the Consolidated Statements of Financial Condition. The following table presents the remaining scheduled accretion of the intangible liability by year. Scheduled Accretion of Operating Lease Intangible (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 935 2019 685 2020 648 2021 648 2022 639 2023 and thereafter 3,358 Total accretion $ 6,913 The following table presents net operating lease expense for the years ended December 31, 2017 , 2016 , and 2015 . Net Operating Lease Expense (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Lease expense charged to operations $ 18,666 $ 11,207 $ 6,850 Accretion of operating lease intangible (1) (1,180 ) (1,171 ) (1,144 ) Accretion of deferred gain on sale-leaseback transaction (1) (5,872 ) (1,473 ) — Rental income from premises leased to others (1) (682 ) (527 ) (606 ) Net operating lease expense $ 10,932 $ 8,036 $ 5,100 (1) Included as reductions to net occupancy and equipment expense in the Consolidated Statements of Income.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	GOODWILL AND OTHER INTANGIBLE ASSETS The Company's annual goodwill impairment test was performed as of October 1, 2017 . It was determined that no impairment existed as of that date or as of December 31, 2017 . For a discussion of the accounting policies for goodwill and other intangible assets, see Note 1 , " Summary of Significant Accounting Policies ." The following table presents changes in the carrying amount of goodwill for the years ended December 31, 2017 , 2016 , and 2015 . Changes in the Carrying Amount of Goodwill (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 340,879 $ 319,007 $ 310,589 Acquisitions 356,729 21,872 8,418 Ending balance $ 697,608 $ 340,879 $ 319,007 The increase in goodwill for the year ended December 31, 2017 resulted from the Standard and Premier acquisitions and measurement period adjustments related to finalizing the fair values of the assets acquired and liabilities assumed in the NI Bancshares acquisition. During the year ended December 31, 2016 the increase resulted from the NI Bancshares acquisition and measurement period adjustments related to finalizing the fair values of the assets acquired and liabilities assumed in the Peoples Bancorp, Inc. ("Peoples") acquisition. During the year ended December 31, 2015 , the increase in goodwill resulted from the Peoples acquisition and measurement period adjustments related to finalizing the fair values of the assets acquired and liabilities assumed in the Great Lakes Financial Resources, Inc. acquisition. See Note 3 , " Acquisitions ," for additional detail regarding transactions completed in 2017 and 2016. The Company's other intangible assets consist of core deposit intangibles and trust department customer relationship intangibles, which are being amortized over their estimated useful lives. Other intangible assets are subject to impairment testing when events or circumstances indicate that its carrying amount may not be recoverable. The increase in other intangible assets for the year ended December 31, 2017 resulted from the Standard and Premier acquisitions. The increase in other intangible assets for the year ended December 31, 2016 resulted from the NI Bancshares acquisition. During 2017 there were no events or circumstances to indicate impairment. Other Intangible Assets (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Gross Accumulated Amortization Net Beginning balance $ 58,959 $ 32,962 $ 25,997 $ 48,550 $ 28,280 $ 20,270 $ 47,970 $ 24,360 $ 23,610 Additions 39,017 — 39,017 10,409 — 10,409 580 — 580 Amortization expense — 7,865 (7,865 ) — 4,682 (4,682 ) — 3,920 (3,920 ) Ending balance $ 97,976 $ 40,827 $ 57,149 $ 58,959 $ 32,962 $ 25,997 $ 48,550 $ 28,280 $ 20,270 Weighted-average remaining life (in years) 8.3 7.6 7.4 Estimated remaining useful lives (in years) 0.2 to 9.3 0.6 to 9.3 0.8 to 10.0 Scheduled Amortization of Other Intangible Assets (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 7,139 2019 7,073 2020 7,023 2021 6,946 2022 6,867 2023 and thereafter 22,101 Total $ 57,149

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposits	DEPOSITS The following table presents the Company's deposits by type. Summary of Deposits (Dollar amounts in thousands) As of December 31, 2017 2016 Demand deposits $ 3,576,190 $ 2,766,748 Savings deposits 2,011,999 1,615,833 NOW accounts 1,962,304 1,675,421 Money market deposits 1,856,049 1,577,316 Time deposits less than $100,000 904,882 755,558 Time deposits greater than $100,000 741,901 437,727 Total deposits $ 11,053,325 $ 8,828,603 The following table provides maturity information related to the Company's time deposits. Scheduled Maturities of Time Deposits (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 1,086,528 2019 418,176 2020 86,196 2021 38,569 2022 16,845 2023 and thereafter 469 Total $ 1,646,783

Borrowed Funds

Borrowed Funds	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Borrowed Funds	BORROWED FUNDS The following table summarizes the Company's borrowed funds by funding source. Summary of Borrowed Funds (Dollar amounts in thousands) As of December 31, 2017 2016 Securities sold under agreements to repurchase $ 124,884 $ 129,008 FHLB advances 590,000 750,000 Total borrowed funds $ 714,884 $ 879,008 Securities sold under agreements to repurchase are treated as financings and the obligations to repurchase securities sold are included as a liability in the Consolidated Statements of Financial Condition. Repurchase agreements are secured by U.S. treasury and agency securities which are held in third-party pledge accounts, if required. The securities underlying the agreements remain in the respective asset accounts. As of December 31, 2017 , the Company did not have amounts at risk under repurchase agreements with any individual counterparty or group of counterparties that exceeded 10% of stockholders' equity. The Bank is a member of the FHLB and has access to term financing from the FHLB. These advances are secured by designated assets that may include qualifying commercial real estate, residential and multi-family mortgages, home equity loans, and certain municipal and mortgage-backed securities. See Note 5 , " Loans ," for detail of the carrying value of loans pledged. As of December 31, 2017 , FHLB advances had fixed interest rates that range from 1.30% to 1.46% and maturity dates that range from January 2, 2018 to March 1, 2018. The Company hedges interest rates on borrowed funds using interest rate swaps through which the Company receives variable amounts and pays fixed amounts. See Note 19 " Derivative Instruments and Hedging Activities " for a detailed discussion of interest rate swaps. The following table presents short-term credit lines available for use, for which the Company did not have an outstanding balance as of December 31, 2017 and 2016 . Short-Term Credit Lines Available for Use (Dollar amounts in thousands) As of December 31, 2017 2016 FRBs Discount Window Primary Credit Program $ 843,618 $ 629,699 Available federal funds lines 667,000 632,000 Correspondent bank line of credit 50,000 50,000 On September 27, 2016, the Company entered into a loan agreement with U.S. Bank National Association providing for a $50.0 million short-term, unsecured revolving credit facility. On September 26, 2017, the Company entered into a first amendment to this credit facility, which extends the maturity to September 26, 2018. Advances will bear interest at a rate equal to one-month LIBOR plus 1.75% , adjusted on a monthly basis, and the Company must pay an unused facility fee equal to 0.35% per annum on a quarterly basis. Management may use this line of credit for general corporate purposes. As of December 31, 2017 , no amount was outstanding under the facility. None of the Company's borrowings have any related compensating balance requirements that restrict the use of Company assets.

Senior and Subordinated Debt

Senior and Subordinated Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Senior and Subordinated Debt	SENIOR AND SUBORDINATED DEBT The following table presents the Company's senior and subordinated debt by issuance. Senior and Subordinated Debt (Dollar amounts in thousands) As of December 31, Issuance Date Maturity Date Interest Rate 2017 2016 Subordinated notes September 2016 September 2026 5.875% $ 146,927 $ 146,573 Junior subordinated debentures: First Midwest Capital Trust I ("FMCT") November 2003 December 2033 6.950% 37,801 37,800 Great Lakes Statutory Trust II ("GLST II") (1) December 2005 December 2035 L+1.400% (2) 4,486 4,391 Great Lakes Statutory Trust III ("GLST III") (1) June 2007 September 2037 L+1.700% (2) 5,956 5,839 Total junior subordinated debentures 48,243 48,030 Total senior and subordinated debt $ 195,170 $ 194,603 (1) The junior subordinated debentures related to GLST II and GLST III were assumed by the Company through an acquisition. As of December 31, 2017, these amounts include acquisition adjustments which resulted in a discount of $1.7 million to GLST II and $2.3 million to GLST III. The acquisition adjustments totaled $1.8 million and $2.4 million to GLST II and GLST III, respectively, as of December 31, 2016. (2) The interest rates are a variable rate based on the three-month LIBOR plus 1.400% and 1.700% for GLST II and GLST III, respectively. On April 1, 2016, $38.5 million of 5.850% subordinated notes matured and were repaid by the Company and on November 22, 2016, $115.0 million of 5.875% senior notes matured and were repaid by the Company. Issuance of Subordinated Notes On September 29, 2016, the Company completed the issuance and sale of $150.0 million aggregate principal amount of its 5.875% subordinated notes due 2026. Interest on the notes is payable semi-annually on March 29 and September 29, beginning on March 29, 2017. The Company received proceeds of $146.5 million , net of underwriting discounts and commissions and issuance costs. The Company used the net proceeds to repay at maturity the entire $115.0 million aggregate principal amount of its 5.875% senior notes on November 22, 2016, plus accrued interest, and for other general corporate purposes. Junior Subordinated Debentures FMCT, GLST II and GLST III are Delaware statutory business trusts. These trusts were established for the purpose of issuing trust-preferred securities and lending the proceeds to the Company in return for junior subordinated debentures of the Company. The junior subordinated debentures are the sole assets of each trust. Therefore, each trust's ability to pay amounts due on the trust-preferred securities is solely dependent on the Company making payments on the related junior subordinated debentures. The trust-preferred securities are subject to mandatory redemption, in whole or in part, on repayment of the junior subordinated debentures at the stated maturity date or on redemption. The Company guarantees payments of distributions and redemptions on the trust-preferred securities on a limited basis. Trust-preferred securities are included in Tier 1 capital of the Company for regulatory capital purposes. The statutory trusts qualify as variable interest entities for which the Company is not the primary beneficiary. Consequently, the accounts of those entities are not consolidated in the Company's financial statements.

Material Transactions Affecting

Material Transactions Affecting Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Material Transactions Affecting Stockholders' Equity	MATERIAL TRANSACTIONS AFFECTING STOCKHOLDERS' EQUITY Issued Common Stock On January 6, 2017, the Company issued 21,057,085 shares of its $0.01 par value common stock at a price of $25.34 as part of the consideration in the Standard acquisition. Additional information regarding the Standard acquisition is presented in Note 3 , " Acquisitions ." On March 8, 2016, the Company issued 3,042,494 shares of its $0.01 par value common stock at a price of $18.059 as part of the consideration in the NI Bancshares acquisition. Additional information regarding the NI Bancshares acquisition is presented in Note 3 , " Acquisitions ." Authorized Common Stock On May 17, 2017, the Company's stockholders approved and adopted an amendment to the Company's Restated Certificate of Incorporation. The amendment increased the Company's authorized common stock by 100,000,000 shares. Following this amendment, the Company is now authorized to issue a total of 251,000,000 shares, including 1,000,000 shares of Preferred Stock, without a par value, and 250,000,000 shares of Common Stock, $0.01 par value per share. Quarterly Dividend on Common Shares The Company's Board of Directors ("the Board") declared cash dividends on the Company's common stock of $0.09 per share for the first quarter of 2015, and $0.09 per share for each of the quarters through the first quarter of 2017. The Company increased the quarterly dividend to $0.10 per share for each of the quarters from the second quarter of 2017 through the fourth quarter of 2017. Other than share-based compensation which is disclosed in Note 17 , " Share-Based Compensation ", there were no additional material transactions that affected stockholders' equity during the three years ended December 31, 2017 .

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	EARNINGS PER COMMON SHARE The table below displays the calculation of basic and diluted EPS. Basic and Diluted EPS (Amounts in thousands, except per share data) Years Ended December 31, 2017 2016 2015 Net income $ 98,387 $ 92,349 $ 82,064 Net income applicable to non-vested restricted shares (916 ) (1,043 ) (882 ) Net income applicable to common shares $ 97,471 $ 91,306 $ 81,182 Weighted-average common shares outstanding: Weighted-average common shares outstanding (basic) 101,423 79,797 77,059 Dilutive effect of common stock equivalents 20 13 13 Weighted-average diluted common shares outstanding 101,443 79,810 77,072 Basic EPS $ 0.96 $ 1.14 $ 1.05 Diluted EPS 0.96 1.14 1.05 Anti-dilutive shares not included in the computation of diluted EPS (1) 229 494 800 (1) This amount represents outstanding stock options for which the exercise price is greater than the average market price of the Company's common stock.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Components of Income Tax Expense (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Current income tax expense: Federal $ 93,540 $ 46,748 $ 18,524 State 104 790 2,326 Total 93,644 47,538 20,850 Deferred income tax (benefit) expense: Federal (12,219 ) (7,786 ) 12,048 State 8,142 6,419 4,849 Total (4,077 ) (1,367 ) 16,897 Total income tax expense $ 89,567 $ 46,171 $ 37,747 The Tax Cuts and Jobs Act ("federal income tax reform") was enacted on December 22, 2017. Among other things, the new law (i) establishes a new, flat corporate federal statutory income tax rate of 21%, (ii) eliminates the corporate alternative minimum tax ("AMT") and allows the use of any such carryforwards to offset regular tax liability for any taxable year, (iii) limits the deduction for net interest expense incurred by U.S. corporations, (iv) allows businesses to immediately expense, for tax purposes, the cost of new investments in certain qualified depreciable assets, (v) eliminates or reduces certain deductions related to meals and entertainment expenses, (vi) modifies the limitation on excessive employee remuneration to eliminate the exception for performance-based compensation and clarifies the definition of a covered employee, and (vii) limits the deductibility of deposit insurance premiums. Federal income tax reform also significantly changes U.S. tax law related to foreign operations, however, such changes do not currently impact the Company. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 ("SAB 118") to address the application of U.S. GAAP in situations when an entity does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of federal income tax reform. SAB 118 provides guidance on accounting for the effects of federal income tax reform where the Company's determinations are incomplete but the Company is able to determine a reasonable estimate. A final determination is required to be made within a measurement period not to extend beyond one year from the enactment date of federal income tax reform. As of December 31, 2017, the Company has completed the majority of its accounting for the tax effects of federal income tax reform. The Company has recognized provisional adjustments for the revaluation of deferred tax assets to reflect the reduced rate that will apply in future periods when these deferred taxes are settled and realized. Although the tax rate reduction is known, the Company has not fully collected all of the necessary data to complete its analysis of the effect of federal income tax reform on the underlying deferred taxes and as such, the amounts recorded as of December 31, 2017 are provisional. Any subsequent adjustment to these amounts, if any, will be recorded to income tax expense during 2018. Federal income tax expense and the related effective income tax rate are influenced by the amount of tax-exempt income derived from investment securities and BOLI in relation to pre-tax income as well as state income taxes. 2017 current federal income tax expense included $26.6 million for the fourth quarter revaluation of deferred tax assets as a result of federal income tax reform. This revaluation adjustment remains preliminary and may change as the Company completes the accounting for the federal income tax reform. State income tax expense and the related effective income tax rate are driven by both the amount of state tax-exempt income in relation to pre-tax income and state tax rules for consolidated/combined reporting and sourcing of income and expense. 2017 current state income tax included a $2.8 million benefit recorded in the third quarter due to a change in the Illinois income tax rate. Components of Effective Tax Rate (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Amount % of Pretax Income Amount % of Pretax Income Amount % of Pretax Income Statutory federal income tax $ 65,784 35.0 % $ 48,482 35.0 % $ 41,934 35.0 % Increase (decrease) in income taxes resulting from: Revaluation of deferred tax assets 23,709 12.6 — — — — Tax-exempt income, net of interest expense disallowance (5,065 ) (2.7 ) (5,439 ) (3.9 ) (6,752 ) (5.6 ) State income tax, net of federal income tax effect 5,069 2.7 4,323 3.1 4,665 3.9 Other 70 0.1 (1,195 ) (0.9 ) (2,100 ) (1.8 ) Total $ 89,567 47.7 % $ 46,171 33.3 % $ 37,747 31.5 % The increase in income tax expense and the effective tax rate from the years ended December 31, 2016 to 2017 was due primarily to higher pre-tax income subject to tax at statutory rates, the $26.6 million downward revaluation of deferred tax assets as a result of federal income tax reform, partly offset by a $2.8 million benefit due to a change in the Illinois income tax rate. The increase in income tax expense and the effective tax rate from the years ended December 31, 2015 to 2016 resulted primarily from an increase in income subject to tax at statutory rates, partially offset by decreases in state statutory rates. As of December 31, 2017 , 2016 , and 2015 , the Company's retained earnings included an appropriation for an acquired thrift's tax bad debt reserves of approximately $2.5 million for which no provision for federal or state income taxes has been made. If, in the future, this portion of retained earnings were distributed as a result of the liquidation of the Company or its subsidiaries, federal and state income taxes would be imposed at the then applicable rates. Differences between the amounts reported in the consolidated financial statements and the tax basis of assets and liabilities result in temporary differences for which deferred tax assets and liabilities were recorded. Deferred Tax Assets and Liabilities (Dollar amounts in thousands) As of December 31, 2017 2016 Deferred tax assets: Allowance for credit losses $ 20,285 $ 30,399 Deferred gain on sale-leaseback transaction 15,668 28,133 Equity based compensation 3,605 5,228 Federal and state net operating loss ("NOL") carryforwards 3,384 388 Acquisition adjustments 2,489 — OREO 2,089 4,336 Non-equity based compensation 897 6,060 AMT and other credit carryforwards 667 90 Unrealized losses on securities 23 18,320 Other 12,494 10,997 Total deferred tax assets 61,601 103,951 Deferred tax liabilities: Deferred loan fees and costs (4,169 ) (3,172 ) Accrued retirement benefits (3,517 ) (6,281 ) Fixed assets (1,660 ) (397 ) Cancellation of indebtedness income (641 ) (2,136 ) Acquisition adjustments — (13,407 ) Other (2,449 ) (6,045 ) Total deferred tax liabilities (12,436 ) (31,438 ) Deferred tax valuation allowance — — Net deferred tax assets 49,165 72,513 Tax effect of adjustments related to other comprehensive income (loss) 15,571 27,694 Net deferred tax assets including adjustments $ 64,736 $ 100,207 NOL carryforwards available to offset future taxable income: Federal gross NOL carryforwards, begin to expire in 2035 $ — $ 574 Illinois gross NOL carryforwards, begin to expire in 2025 188,995 26,342 Indiana gross NOL carryforwards, begin to expire in 2025 16,174 1,003 AMT credits 410 — During the year ended December 31, 2017, the Company recorded net deferred tax assets of $41.5 million related to the Standard acquisition and a measurement period adjustment related to finalizing the fair values of the assets acquired and liabilities assumed in the NI Bancshares acquisition. During the year ended December 31, 2016, the Company recorded net deferred tax assets of $4.4 million related to the NI Bancshares acquisition and a measurement period adjustment related to finalizing the fair values of the assets acquired and liabilities assumed in the Peoples acquisition. During the years ended December 31, 2017 and 2016, the Company transferred certain loans into Real Estate Mortgage Investment Conduit trusts which are classified as loans in the financial statements and as securities for tax purposes. Net deferred tax assets are included in other assets in the accompanying Consolidated Statements of Financial Condition. Management believes that it is more likely than not that net deferred tax assets will be fully realized and no valuation allowance is required. Uncertainty in Income Taxes The Company files a U.S. federal income tax return and state income tax returns in various states. Income tax returns filed by the Company are no longer subject to examination by federal and state income tax authorities for years prior to 2014 . Rollforward of Unrecognized Tax Benefits (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 2,039 $ 1,408 $ 912 Additions for tax positions relating to the current year 845 640 480 Additions for tax positions relating to prior years 13,389 — 37 Reductions for tax positions relating to prior years (25 ) (9 ) (21 ) Ending balance $ 16,248 $ 2,039 $ 1,408 Interest and penalties not included above (1) : Interest expense, net of tax effect, and penalties $ 118 $ 49 $ 20 Accrued interest and penalties, net of tax effect, at end of year 191 73 24 (1) Included in income tax expense in the Consolidated Statements of Income. The Company does not anticipate that the amount of uncertain tax positions will significantly increase or decrease in the next twelve months. Included in the balance as of December 31, 2017 , 2016 , and 2015 are tax positions totaling $12.9 million , $1.4 million and $936,000 , respectively, which would favorably affect the Company's effective tax rate if recognized in future periods.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS Profit Sharing Plan The Company has a defined contribution retirement savings plan (the "Profit Sharing Plan") that covers qualified employees who meet certain eligibility requirements. During 2014, the Profit Sharing Plan was amended to give qualified employees the option to increase contributions from 45% ( 15% for certain highly compensated employees) to 100% (including certain highly compensated employees) of their pre-tax base salary through salary deductions under Section 401(k) of the Internal Revenue Code. At the employees' direction, employee contributions are invested among a variety of investment alternatives. The amendment also increased the Company's matching contribution from a maximum of 2% to 4% of the eligible employee's compensation. In addition, pursuant to the amendment, the Company makes certain automatic and transition contributions. On an annual basis, the Company automatically contributes 2% of the employee's eligible compensation regardless of voluntary contributions made by the employee. Transition contributions of up to 4% were made through December 31, 2015 for certain employees who were active participants in the defined benefit retirement plan (the "Pension Plan"), which was frozen in 2013. The amendment did not change the discretionary profit sharing component of the Profit Sharing Plan, which permits the Company to distribute up to 15% of the employee's compensation. The Company's matching and transition contributions vest immediately, while the automatic and discretionary components vest over six years. Profit Sharing Plan (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Profit sharing expense (1) $ 7,346 $ 6,171 $ 6,919 Company dividends received by the Profit Sharing Plan $ 441 $ 494 $ 466 Company shares held by the Profit Sharing Plan at the end of the year: Number of shares 1,079,975 1,175,858 1,277,567 Fair value $ 25,930 $ 29,667 $ 23,546 (1) Included in retirement and other employee benefits in the Consolidated Statements of Income. Pension Plan The Company sponsors the Pension Plan which provides for retirement benefits based on years of service and compensation levels of the participants. The Pension Plan covers employees who met certain eligibility requirements and were hired before April 1, 2007, the date it was amended to eliminate new enrollment of new participants. During 2013, the Board approved an amendment to freeze benefit accruals under the Pension Plan effective on January 1, 2014. Actuarially determined pension costs are charged to current operations and included in retirement and other employee benefits in the Consolidated Statements of Income. The Company's funding policy is to contribute amounts to the Pension Plan that are sufficient to meet the minimum funding requirements of the Employee Retirement Income Security Act of 1974 plus additional amounts as the Company deems appropriate. Pension Plan Cost and Obligations (Dollar amounts in thousands) As of December 31, 2017 2016 Accumulated benefit obligation $ 67,923 $ 68,959 Change in projected benefit obligation Beginning balance $ 68,959 $ 67,185 Service cost — — Interest cost 1,712 1,635 Settlements (6,271 ) (3,136 ) Actuarial loss 4,240 3,851 Benefits paid (717 ) (576 ) Ending balance $ 67,923 $ 68,959 Change in fair value of plan assets Beginning balance $ 65,189 $ 64,903 Actual return on plan assets 7,958 3,998 Benefits paid (717 ) (576 ) Settlements (6,271 ) (3,136 ) Ending balance $ 66,159 $ 65,189 Funded status recognized in the Consolidated Statements of Financial Condition Noncurrent liability $ (1,764 ) $ (3,770 ) Amounts recognized in accumulated other comprehensive loss Prior service cost $ — $ — Net loss 25,495 28,483 Net amount recognized $ 25,495 $ 28,483 Actuarial losses included in accumulated other comprehensive loss as a percent of Accumulated benefit obligation 37.5 % 41.3 % Fair value of plan assets 38.5 % 43.7 % Amounts expected to be amortized from accumulated other comprehensive loss into net periodic benefit cost in the next fiscal year Prior service cost $ — $ — Net loss 561 582 Net amount expected to be recognized $ 561 $ 582 Weighted-average assumptions at the end of the year used to determine the actuarial present value of the projected benefit obligation Discount rate 3.45 % 3.86 % On December 31, 2015, the Company refined the calculation of the interest component of net periodic benefit expense for the Pension Plan. Previously, the Company estimated the interest cost component utilizing a single weighted-average discount rate derived from the yield curve used to measure the benefit obligation at the end of the period. Under the refined method, the Company utilized a full yield curve approach to estimate the component by applying specific spot rates along the yield curve used in the determination of the benefit obligation to the relevant projected cash flows. The Company made this change to more closely match the projected benefit cash flows and the corresponding yield curve spot rates, and to provide a more precise measurement of interest costs. This change had no impact on the measurement of the Company's total benefit obligations recorded as of December 31, 2015. The Company accounted for this change as a change in estimate that is inseparable from a change in accounting principle, and, accordingly, recognized its effect prospectively beginning in 2016. To the extent the cumulative actuarial losses included in accumulated other comprehensive loss exceed 10% of the greater of the accumulated benefit obligation or the market-related value of the Pension Plan assets, it is the Company's policy to amortize the Pension Plan's net actuarial losses into income over the average remaining life expectancy of the Pension Plan participants. Actuarial losses included in accumulated other comprehensive loss as of December 31, 2017 exceeded 10% of the accumulated benefit obligation and the fair value of Pension Plan assets. The amortization of net actuarial losses is a component of the net periodic benefit cost. Amortization of the net actuarial losses and prior service cost included in other comprehensive income (loss) is not expected to have a material impact on the Company's future results of operations, financial position, or liquidity. Net Periodic Benefit Pension Cost (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Components of net periodic benefit cost Interest cost $ 1,712 $ 1,635 $ 2,334 Expected return on plan assets (3,802 ) (4,057 ) (4,333 ) Recognized net actuarial loss 591 571 367 Amortization of prior service cost — — — Recognized settlement loss 2,480 1,338 2,254 Net periodic cost (income) 981 (513 ) 622 Other changes in plan assets and benefit obligations recognized as a charge to other comprehensive income (loss) Net loss for the period (83 ) (3,911 ) (9,191 ) Amortization of net loss 3,071 1,909 2,621 Total unrealized gain (loss) 2,988 (2,002 ) (6,570 ) Total recognized in net periodic pension cost and other comprehensive income (loss) $ 2,007 $ (1,489 ) $ (7,192 ) Weighted-average assumptions used to determine the net periodic cost Discount rate 3.86 % 3.99 % 3.60 % Expected return on plan assets 6.25 % 6.50 % 6.50 % Pension Plan Asset Allocation (Dollar amounts in thousands) Percentage of Plan Assets as of December 31, Target Allocation Fair Value of Plan Assets (1) 2017 2016 Asset Category Equity securities 50 - 60% $ 39,954 60 % 60 % Fixed income 30 - 48% 22,734 35 % 33 % Cash equivalents 2 - 10% 3,471 5 % 7 % Total $ 66,159 100 % 100 % (1) Additional information regarding the fair value of Pension Plan assets as of December 31, 2017 can be found in Note 21 , " Fair Value ." The expected long-term rate of return on Pension Plan assets represents the average rate of return expected to be earned over the period the benefits included in the benefit obligation are to be paid. In developing the expected rate of return, the Company considers long-term returns based on historical market data and projections of future returns for each asset category, as well as historical actual returns on the Pension Plan assets with the assistance of its independent actuarial consultant. Using this reference data, the Company develops a forward-looking return expectation for each asset category and a weighted-average expected long-term rate of return based on the target asset allocation. The investment objective of the Pension Plan is to maximize the return on Pension Plan assets over a long-term horizon to satisfy the Pension Plan obligations. In establishing its investment policies and asset allocation strategies, the Company considers expected returns and the volatility associated with different strategies. The policy established by the Company's Retirement Plan Committee provides for growth of capital with a moderate level of volatility by investing assets according to the target allocations stated above and reallocating those assets as needed to stay within those allocations. Investments are weighted toward publicly traded securities. Investment strategies that include alternative asset classes, such as private equity hedge funds and real estate, are generally avoided. Under the advisement of a certified investment advisor, the Committee reviews the investment policy on a quarterly basis to determine if any adjustments to the policy or investment strategy are necessary. The following table presents estimated future pension benefit payments under the Pension Plan for retirees already receiving benefits and future retirees, assuming they retire and begin receiving unreduced benefits as soon as they are eligible. Estimated Future Pension Benefit Payments (Dollar amounts in thousands) Total Year ending December 31, 2018 $ 6,849 2019 5,462 2020 5,366 2021 5,216 2022 5,064 2023-2026 20,222

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	SHARE-BASED COMPENSATION Share-Based Plans Omnibus Stock and Incentive Plan (the "Omnibus Plan") – In 1989, the Board adopted the Omnibus Plan, which allows for the grant of both incentive and non-statutory ("nonqualified") stock options, stock appreciation rights, restricted stock, restricted stock units, performance units, and performance shares to certain key employees. From the inception of the Omnibus Plan through the end of 2008, certain key employees were granted nonqualified stock options. The option exercise price is the average of the high and low price of the Company's common stock on the grant date. All options have a term of 10 years from the grant date and are non-transferable except to immediate family members, family trusts, or partnerships. Since 2008, the Company has granted restricted stock and restricted stock unit awards instead of nonqualified stock options to certain key employees. Both restricted stock and restricted stock unit awards vest over three years, with 50% vesting on the second anniversary of the grant date and the remaining 50% vesting on the third anniversary of the grant date, provided the employee remains employed by the Company during this period (subject to accelerated vesting under certain circumstances in the event of a change-in-control or upon certain terminations of employment, as set forth in the applicable award agreement). The fair value of the awards is determined based on the average of the high and low price of the Company's common stock on the grant date. Since 2013, the Company has also granted performance shares to certain key employees. Recipients will earn performance shares totaling between 0% and 200% of the number of performance shares granted based on achieving certain performance metrics. Performance shares may be earned based on achieving an internal metric (core return on average tangible common equity) and an external metric (relative total shareholder return) over a three year period. Each metric is weighted at 50% of the total award opportunity. If earned, and assuming continued employment, the performance shares vest one-third at the completion of the three-year performance period and one-third at the end of the first and second years thereafter. The fair value of the performance shares that are dependent on the internal metric is determined based on the average of the high and low stock price on the grant date. An estimate is made as to the number of shares expected to vest as a result of actual performance against the internal metric to determine the amount of compensation expense to be recognized, which is re-evaluated quarterly. The fair value of the performance shares that are dependent on the external metric is determined using a Monte Carlo simulation model on the grant date assuming 100% of the shares are earned and issued. Nonemployee Directors Stock Plan (the "Directors Plan") – In 1997, the Board adopted the Directors Plan, which provides for the grant of equity awards to non-management Board members. Until 2008, only nonqualified stock options were issued under the Directors Plan. The exercise price of the options is equal to the average of the high and low price of the Company's common stock on the grant date. All options have a term of 10 years from the grant date. In 2008, the Company amended the Directors Plan to allow for the grant of restricted stock awards, among other items. The awards are restricted as to transfer, but are not restricted as to voting rights. Dividends accrue and are paid at the vesting date. Both the options and the restricted stock awards vest one year from the grant date subject to accelerated vesting in the event of retirement, death, disability, or change-in-control, as defined in the Directors Plan. Since 2015, non-management members receive fully vested shares of the Company's common stock rather than restricted stock. Both the Omnibus Plan and the Directors Plan, and material amendments, were submitted to and approved by the stockholders of the Company. The Company issues treasury shares to satisfy stock option exercises and the vesting of restricted stock, restricted stock units, and performance share awards. Shares of Common Stock Available Under Share-Based Plans As of December 31, 2017 Shares Authorized Shares Available For Grant Omnibus Plan 8,631,641 1,835,929 Directors Plan 481,250 104,782 Stock Options Nonqualified Stock Option Transactions (Amounts in thousands, except per share data) Year Ended December 31, 2017 Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (1) Aggregate Intrinsic Value (2) Options outstanding beginning balance 486 $ 31.77 Expired (254 ) 37.78 Options outstanding ending balance 232 $ 25.19 0.75 $ 513 Exercisable at the end of the year 232 $ 25.19 0.75 $ 513 (1) Represents the average remaining contractual life in years. (2) Aggregate intrinsic value represents the total pre-tax intrinsic value that would have been received by the option holders if they had exercised their options on December 31, 2017 . Intrinsic value equals the difference between the Company's average of the high and low stock price on the last trading day of the year and the option exercise price, multiplied by the number of shares. This amount will fluctuate with changes in the fair value of the Company's common stock. Stock Option Valuation Assumptions – The Company estimates the fair value of stock options at the grant date using a Black-Scholes option-pricing model. No stock options were granted or exercised and no stock option award modifications were made during the three years ended December 31, 2017 . Restricted Stock, Restricted Stock Unit, and Performance Share Awards Restricted Stock, Restricted Stock Unit, and Performance Share Award Transactions (Amounts in thousands, except per share data) Year Ended December 31, 2017 Restricted Stock/Unit Awards Performance Shares Number of Shares/Units Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Non-vested awards beginning balance 989 $ 16.95 408 $ 15.78 Granted 477 24.71 145 24.71 Vested (367 ) 16.79 (54 ) 16.79 Forfeited (46 ) 19.80 (33 ) 19.80 Non-vested awards ending balance 1,053 $ 20.36 466 $ 18.16 In addition, non-management board members received, in the aggregate, 16,000 shares and 18,000 shares of common stock during the years ended December 31, 2017 and 2016 , respectively. Other Restricted Stock, Restricted Stock Unit, and Performance Share Award Information (Amounts in thousands, except per share data) Years Ended December 31, 2017 2016 2015 Weighted-average grant date fair value of restricted stock, restricted stock unit, and performance share awards granted during the year $ 24.71 $ 17.28 $ 16.95 Total fair value of restricted stock, restricted stock unit, and performance share awards vested during the year 13,760 12,231 7,615 Income tax benefit realized from the vesting/release of restricted stock, restricted stock unit, and performance share awards 4,007 2,529 2,368 No restricted stock, restricted stock unit, or performance share award modifications were made during the periods presented. Compensation Expense The Company recognizes share-based compensation expense based on the estimated fair value of the option or award at the grant or modification date. Share-based compensation expense is included in salaries and wages in the Consolidated Statements of Income. Effect of Recording Share-Based Compensation Expense (Dollar amounts in thousands) Years ended December 31, 2017 2016 2015 Total share-based compensation expense (1) $ 11,223 $ 7,879 $ 7,242 Income tax benefit 4,601 3,152 2,962 Share-based compensation expense, net of tax $ 6,622 $ 4,727 $ 4,280 Unrecognized compensation expense $ 13,266 $ 9,990 $ 8,644 Weighted-average amortization period remaining (in years) 1.3 1.3 1.4 (1) Comprised of restricted stock, restricted stock unit, and performance share awards expense.

Regulatory and Capital Matters

Regulatory and Capital Matters	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Regulatory and Capital Matters	REGULATORY AND CAPITAL MATTERS The Company and its subsidiaries are subject to various regulatory requirements that impose restrictions on cash, loans or advances, and dividends. The Bank is also required to maintain reserves against deposits. Reserves are held either in the form of vault cash or noninterest-bearing balances maintained with the FRB and are based on the average daily balances and statutory reserve ratios prescribed by the type of deposit account. Reserve balances totaling $121.0 million as of December 31, 2017 and $85.4 million as of December 31, 2016 were maintained in accordance with these requirements. Under current Federal Reserve regulations, the Bank is limited in the amount it may loan or advance to First Midwest Bancorp, Inc. on an unconsolidated basis (the "Parent Company") and its non-bank subsidiaries. Loans or advances to a single subsidiary may not exceed 10% , and loans to all subsidiaries may not exceed 20% , of the Bank's capital stock and surplus. Loans from subsidiary banks to non-bank subsidiaries, including the Parent Company, are also required to be collateralized. The principal source of cash flow for the Parent Company is dividends from the Bank. Various federal and state banking regulations and capital guidelines limit the amount of dividends that the Bank may pay to the Parent Company. Without prior regulatory approval and while maintaining its well-capitalized status, the Bank can initiate aggregate dividend payments in 2018 of $107.8 million plus its net profits for 2018 , as defined by statute, up to the date of any such dividend declaration. Future payment of dividends by the Bank depends on individual regulatory capital requirements and levels of profitability. The Company and the Bank are also subject to various capital requirements set up and administered by federal banking agencies. Under capital adequacy guidelines, the Company and the Bank must meet specific guidelines that involve quantitative measures given the risk levels of assets and certain off-balance sheet items calculated under regulatory accounting practices ("risk-weighted assets"). The capital amounts and classification are also subject to qualitative judgments by the regulators regarding components of capital and assets, risk weightings, and other factors. The Federal Reserve, the primary regulator of the Company and the Bank, establishes minimum capital requirements that must be met by the Company and the Bank. As defined in the regulations, quantitative measures established by regulation to ensure capital adequacy require the Company and the Bank to maintain minimum amounts and ratios of total capital to risk-weighted assets, Tier 1 capital to risk-weighted assets, common equity Tier 1 ("CET1") to risk-weighted assets, and Tier 1 capital to adjusted average assets. Failure to meet minimum capital requirements could result in actions by regulators that could have a material adverse effect on the Company's financial statements. As of December 31, 2017 , the Company and the Bank met all capital adequacy requirements. As of December 31, 2017 , the Bank was "well-capitalized" under the regulatory framework for prompt corrective action. There are no conditions or events since that management believes would change the Bank's classification. The following table outlines the Company's and the Bank's measures of capital as of the dates presented and the capital guidelines established by the Federal Reserve for the Company and the Bank to be categorized as adequately capitalized and the Bank to be categorized as "well-capitalized." Summary of Regulatory Capital Ratios (Dollar amounts in thousands) Actual Adequately Capitalized To Be Well-Capitalized Under Prompt Corrective Action Provisions Capital Ratio % Capital Ratio % Capital Ratio % As of December 31, 2017 Total capital to risk-weighted assets: First Midwest Bancorp, Inc. $ 1,448,124 12.15 $ 1,102,634 9.250 N/A N/A First Midwest Bank 1,300,809 10.95 1,099,133 9.250 $ 1,188,252 10.00 Tier 1 capital to risk-weighted assets: First Midwest Bancorp, Inc. 1,204,468 10.10 864,227 7.250 N/A N/A First Midwest Bank 1,204,080 10.13 861,482 7.250 950,601 8.00 CET1 to risk-weighted assets: First Midwest Bancorp, Inc. 1,153,939 9.68 685,421 5.750 N/A N/A First Midwest Bank 1,204,080 10.13 683,245 5.750 772,364 6.50 Tier 1 capital to average assets: First Midwest Bancorp, Inc. 1,204,468 8.99 536,200 4.000 N/A N/A First Midwest Bank 1,204,080 9.10 529,147 4.000 661,434 5.00 As of December 31, 2016 Total capital to risk-weighted assets: First Midwest Bancorp, Inc. $ 1,225,529 12.23 $ 864,176 8.625 N/A N/A First Midwest Bank 1,043,482 10.73 838,741 8.625 $ 972,454 10.00 Tier 1 capital to risk-weighted assets: First Midwest Bancorp, Inc. 991,873 9.90 663,788 6.625 N/A N/A First Midwest Bank 956,399 9.83 644,251 6.625 777,963 8.00 CET1 to risk-weighted assets: First Midwest Bancorp, Inc. 941,315 9.39 513,496 5.125 N/A N/A First Midwest Bank 956,399 9.83 498,383 5.125 632,095 6.50 Tier 1 capital to average assets: First Midwest Bancorp, Inc. 991,873 8.99 441,473 4.000 N/A N/A First Midwest Bank 956,399 8.76 436,560 4.000 545,700 5.00 N/A – Not applicable. In July of 2013, the Federal Reserve published final rules (the "Basel III Capital Rules") that revise the regulatory capital rules to incorporate certain revisions by the Basel Committee on Banking Supervision. The phase-in period for the final rules began for the Company on January 1, 2015, with full compliance with the entire requirements of the final rules phased in on January 1, 2019. The Basel III Capital Rules, among other things (i) introduced a new capital measure called CET1, (ii) specified that Tier 1 capital consists of CET1 and "Additional Tier 1 Capital" instruments meeting specified requirements, (iii) narrowly defined CET1 by requiring that most deductions/adjustments to regulatory capital measures be made to CET1 and not to the other components of capital, and (iv) expanded the scope of the deductions/adjustments compared to existing regulations. Bank holding companies with less than $15 billion in consolidated assets as of December 31, 2009, such as the Company, are permitted to include trust-preferred securities in Additional Tier 1 Capital. This treatment is permanently grandfathered as Tier 1 capital even if the Company should ever exceed $15 billion in consolidated assets due to organic growth. Should the Company exceed $15 billion in consolidated assets as the result of a merger or acquisition, then the Tier 1 treatment of its outstanding trust-preferred securities will be phased out, but those securities will be treated as Tier 2 capital. As of December 31, 2017 , the Company had $50.7 million of trust-preferred securities included in Tier 1 capital. When fully phased in on January 1, 2019, the Basel III Capital Rules will require the Company and the Bank to maintain the following: • A minimum ratio of CET1 to risk-weighted assets of at least 4.5% , plus a 2.5% "capital conservation buffer" (resulting in a minimum ratio of CET1 to risk-weighted assets of at least 7.0% upon full implementation). • A minimum ratio of Tier 1 capital to risk-weighted assets of at least 6.0% , plus the capital conservation buffer (resulting in a minimum Tier 1 capital ratio of 8.5% upon full implementation). • A minimum ratio of total capital (Tier 1 capital plus Tier 2 capital) to risk-weighted assets of at least 8.0% , plus the capital conservation buffer (resulting in a minimum total capital ratio of 10.5% upon full implementation). • A minimum leverage ratio of 4.0% , calculated as the ratio of Tier 1 capital to average assets. The Basel III Capital Rules also provide for a number of deductions from and adjustments to CET1 to be phased-in over a four -year period through January 1, 2019 (beginning at 40% on January 1, 2015 and an additional 20% per year thereafter). In November of 2017, the Federal Reserve issued a final rule that retained certain existing transition provisions related to deductions from and adjustments to CET1. Examples of these include the requirement that mortgage servicing rights, deferred tax assets depending on future taxable income, and significant investments in non-consolidated financial entities be deducted from CET1 to the extent that any one such category exceeds 10% of CET1 or all such categories in the aggregate exceed 15% of CET1. Under the Basel III Capital Rules, the effects of certain accumulated other comprehensive items are included for purposes of determining regulatory capital ratios; however, the Company and the Bank made a one-time permanent election to continue to exclude these items. Finally, the Basel III Capital Rules prescribe a standardized approach for risk weightings that expand the risk-weighting categories from the prior four Basel I-derived categories ( 0% , 20% , 50% , and 100% ) to a much larger and more risk-sensitive number of categories depending on the nature of the assets, generally ranging from 0% for U.S. government and agency securities to 600% for certain equity exposures, resulting in higher risk weights for a variety of asset categories. The Company and the Bank believe they would meet all capital adequacy requirements under the Basel III Capital Rules on a fully phased-in basis as if such requirements were currently in effect as of December 31, 2017 and 2016. In September of 2017, the federal bank regulators proposed to revise and simplify the capital treatment for certain deferred tax assets, mortgage servicing assets, investments in non-consolidated financial entities and minority interests for banking organizations, such as the Company and the Bank, that are not subject to the advanced approaches framework. In November of 2017, the federal banking regulators revised the Basel III Rules to extend the current transitional treatment of these items for non-advanced approaches banking organizations until the September 2017 proposal is finalized. The September 2017 proposal would also change the capital treatment of certain commercial real estate loans under the standardized approach, which the Company and the Bank use to calculate their capital ratios. In December of 2017, the Basel Committee published standards that it described as the finalization of the Basel III post-crisis regulatory reforms (the standards are commonly referred to as "Basel IV"). Among other things, these standards revise the Basel Committee's standardized approach for credit risk (including the recalibration of risk weights and introducing new capital requirements for certain "unconditionally cancellable commitments," such as unused credit card lines of credit) and provide a new standardized approach for operational risk capital. Under the Basel framework, these standards will generally be effective on January 1, 2022, with an aggregate output floor phasing in through January 1, 2027. Under the current U.S. capital rules, operational risk capital requirements and a capital floor apply only to advanced approaches institutions, and not to the Company or the Bank. The impact of Basel IV on the Company and the Bank will depend on the manner in which it is implemented by the federal bank regulators.

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities	DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES In the ordinary course of business, the Company enters into derivative transactions as part of its overall interest rate risk management strategy. The significant accounting policies related to derivative instruments and hedging activities are presented in Note 1 , " Summary of Significant Accounting Policies ." Fair Value Hedges The Company hedges the fair value of fixed rate commercial real estate loans using interest rate swaps through which the Company pays fixed amounts and receives variable amounts. These derivative contracts are designated as fair value hedges. Fair Value Hedges (Dollar amounts in thousands) As of December 31, 2017 2016 Gross notional amount outstanding $ 5,458 $ 5,958 Derivative liability fair value (101 ) (282 ) Weighted-average interest rate received 3.38 % 2.63 % Weighted-average interest rate paid 5.96 % 5.96 % Weighted-average maturity (in years) 0.84 1.84 Fair value of derivative (1) $ 110 $ 296 (1) This amount represents the fair value if credit risk related contingent features were triggered. Hedge ineffectiveness is recognized in other noninterest income in the Consolidated Statements of Income. For the years ended December 31, 2017 , 2016 , and 2015 , gains or losses related to fair value hedge ineffectiveness were not material. Cash Flow Hedges As of December 31, 2017 , the Company hedged $980.0 million of certain corporate variable rate loans using interest rate swaps through which the Company receives fixed amounts and pays variable amounts. The Company also hedged $980.0 million of borrowed funds using forward starting interest rate swaps through which the Company receives variable amounts and pays fixed amounts. These transactions allow the Company to add stability to net interest income and manage its exposure to interest rate movements. Forward starting interest rate swaps totaling $415.0 million began on various dates between June of 2015 and February of 2017, and mature between June of 2019 and February of 2020. The remaining forward starting interest rate swaps totaling $565.0 million begin on various dates between February of 2018 and February of 2020 and mature between February of 2020 and April of 2022. The weighted-average fixed interest rate to be paid on these interest rate swaps that have not yet begun was 1.96% as of December 31, 2017 . These derivative contracts are designated as cash flow hedges. Cash Flow Hedges (Dollar amounts in thousands) As of December 31, 2017 2016 Gross notional amount outstanding $ 1,960,000 $ 1,470,000 Derivative asset fair value 3,989 5,402 Derivative liability fair value (10,219 ) (7,390 ) Weighted-average interest rate received 1.58 % 1.37 % Weighted-average interest rate paid 1.61 % 1.11 % Weighted-average maturity (in years) 2.25 2.83 The effective portion of gains or losses on cash flow hedges is recorded in accumulated other comprehensive loss on an after-tax basis and is subsequently reclassified to interest income or expense in the period that the forecasted hedged item impacts earnings. Hedge effectiveness is determined using a regression analysis at the inception of the hedge relationship and on an ongoing basis. For the years ended December 31, 2017 and 2016 , there were no material gains or losses related to cash flow hedge ineffectiveness. As of December 31, 2017 , the Company estimates that $1.6 million will be reclassified from accumulated other comprehensive loss as an increase to interest income over the next twelve months. Other Derivative Instruments The Company also enters into derivative transactions through capital market products with its commercial customers and simultaneously enters into an offsetting interest rate derivative transaction with third-parties. These transactions allow the Company's customers to effectively convert a variable rate loan into a fixed rate loan. Due to the offsetting nature of these transactions, the Company does not apply hedge accounting treatment. The Company's credit exposure on these derivative transactions results primarily from counterparty credit risk. The credit valuation adjustment ("CVA") is a fair value adjustment to the derivative to account for this risk. As of December 31, 2017 and 2016 , the Company's credit exposure was fully secured by the underlying collateral on customer loans and mitigated through netting arrangements with third-parties, therefore, no CVA was recorded. Capital market products income related to commercial customer derivative instruments of $8.2 million , $10.0 million , and $4.8 million was recorded in noninterest income for the years ended December 31, 2017 , 2016 , and 2015, respectively. Other Derivative Instruments (Dollar amounts in thousands) As of December 31, 2017 2016 Gross notional amount outstanding $ 2,665,358 $ 1,656,612 Derivative asset fair value 17,079 13,478 Derivative liability fair value (14,930 ) (13,478 ) Fair value of derivative (1) 15,059 13,753 (1) This amount represents the fair value if credit risk related contingent factors were triggered. The Company occasionally enters into risk participation agreements with counterparty banks to transfer or assume a portion of the credit risk related to customer transactions. The amounts of these instruments were not material for any period presented. The Company had no other derivative instruments as of December 31, 2017 and 2016 . The Company does not enter into derivative transactions for purely speculative purposes. Credit Risk Derivative instruments are inherently subject to credit risk, which represents the Company's risk of loss when the counterparty to a derivative contract fails to perform according to the terms of the agreement. Credit risk is managed by limiting and collateralizing the aggregate amount of net unrealized losses by transaction, monitoring the size and the maturity structure of the derivatives, and applying uniform credit standards. Company policy establishes limits on credit exposure to any single counterparty. In addition, the Company established bilateral collateral agreements with derivative counterparties that provide for exchanges of marketable securities or cash to collateralize either party's net losses above a stated minimum threshold. As of December 31, 2017 and 2016 , these collateral agreements covered 100% of the fair value of the Company's outstanding fair value hedges. Derivative assets and liabilities are presented gross, rather than net, of pledged collateral amounts. Certain derivative instruments are subject to master netting agreements with counterparties. The Company records these transactions at their gross fair values and does not offset derivative assets and liabilities in the Consolidated Statements of Financial Condition. The following table presents the fair value of the Company's derivatives and offsetting positions as of December 31, 2017 and 2016 . Fair Value of Offsetting Derivatives (Dollar amounts in thousands) As of December 31, 2017 2016 Assets Liabilities Assets Liabilities Gross amounts recognized $ 21,068 $ 25,250 $ 18,880 $ 21,150 Less: amounts offset in the Consolidated Statements of Financial Condition — — — — Net amount presented in the Consolidated Statements of Financial Condition (1) 21,068 25,250 18,880 21,150 Gross amounts not offset in the Consolidated Statements of Financial Condition: Offsetting derivative positions (16,880 ) (16,880 ) (10,889 ) (10,889 ) Cash collateral pledged — (8,370 ) — (10,261 ) Net credit exposure $ 4,188 $ — $ 7,991 $ — (1) Included in other assets or other liabilities in the Consolidated Statements of Financial Condition. As of December 31, 2017 and 2016 , the Company's derivative instruments generally contained provisions that require the Company's debt to remain above a certain credit rating by each of the major credit rating agencies or that the Company maintain certain capital levels. If the Company's debt were to fall below that credit rating or the Company's capital were to fall below the required levels, it would be in violation of those provisions, and the counterparties to the derivative instruments could terminate the swap transaction and demand cash settlement of the derivative instrument in an amount equal to the derivative liability fair value. As of December 31, 2017 and 2016 , the Company was in compliance with these provisions.

Commitments, Guarantees, and Co

Commitments, Guarantees, and Contingent Liabilities	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments, Guarantees, and Contingent Liabilities	COMMITMENTS, GUARANTEES, AND CONTINGENT LIABILITIES Credit Commitments and Guarantees In the normal course of business, the Company enters into a variety of financial instruments with off-balance sheet risk to meet the financing needs of its customers and to conduct lending activities, including commitments to extend credit and standby and commercial letters of credit. These instruments involve elements of credit and interest rate risk in excess of the amount recognized in the Consolidated Statements of Financial Condition. Contractual or Notional Amounts of Financial Instruments (Dollar amounts in thousands) As of December 31, 2017 2016 Commitments to extend credit: Commercial, industrial, and agricultural $ 1,729,426 $ 1,522,152 Commercial real estate 377,551 397,423 Home equity 514,973 426,384 Other commitments (1) 244,222 214,943 Total commitments to extend credit $ 2,866,172 $ 2,560,902 Letters of credit $ 128,801 $ 100,430 (1) Other commitments includes installment and overdraft protection program commitments. Commitments to extend credit are agreements to lend funds to a customer, subject to contractual terms and covenants. Commitments generally have fixed expiration dates or other termination clauses, variable interest rates, and fee requirements, when applicable. Since many of the commitments are expected to expire without being drawn, the total commitment amounts do not necessarily represent future cash flow requirements. In the event of a customer's non-performance, the Company's credit loss exposure is equal to the contractual amount of the commitments. The credit risk is essentially the same as extending loans to customers for the full contractual amount. The Company uses the same credit policies for credit commitments as its loans and minimizes exposure to credit loss through various collateral requirements. Letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third-party. Letters of credit generally are contingent on the failure of the customer to perform according to the terms of the contract with the third-party and are often issued in favor of a municipality where construction is taking place to ensure the borrower adequately completes the construction. Commercial letters of credit are issued to facilitate transactions between a customer and a third-party based on agreed upon terms. The maximum potential future payments guaranteed by the Company under letters of credit arrangements are equal to the contractual amount of the commitment. If a commitment is funded, the Company may seek recourse through the liquidation of the underlying collateral, including real estate, production plants and property, marketable securities, or receipt of cash. As a result of the sale of certain 1-4 family mortgage loans, the Company is contractually obligated to repurchase early payment default loans or loans that do not meet underwriting requirements at recorded value. In accordance with the sales agreements, there is no limitation to the maximum potential future payments or expiration of the Company's recourse obligation. There were no material loan repurchases during the years ended December 31, 2017 or 2016 . Legal Proceedings In the ordinary course of business, there were certain legal proceedings pending against the Company and its subsidiaries as of December 31, 2017 . While the outcome of any legal proceeding is inherently uncertain, based on information currently available, the Company's management does not expect that any liabilities arising from pending legal matters will have a material adverse effect on the Company's business, financial condition, results of operations, or cash flows.

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value	FAIR VALUE Fair value represents the amount expected to be received to sell an asset or paid to transfer a liability in its principal or most advantageous market in an orderly transaction between market participants at the measurement date. In accordance with fair value accounting guidance, the Company measures, records, and reports various types of assets and liabilities at fair value on either a recurring or non-recurring basis in the Consolidated Statements of Financial Condition. Those assets and liabilities are presented below in the sections titled "Assets and Liabilities Required to be Measured at Fair Value on a Recurring Basis" and "Assets and Liabilities Required to be Measured at Fair Value on a Non-Recurring Basis." Other assets and liabilities are not required to be measured at fair value in the Consolidated Statements of Financial Condition, but must be disclosed at fair value. See the "Fair Value Measurements of Other Financial Instruments" section of this note. Any aggregation of the estimated fair values presented in this note does not represent the value of the Company. Depending on the nature of the asset or liability, the Company uses various valuation methodologies and assumptions to estimate fair value. GAAP provides a three-tiered fair value hierarchy based on the inputs used to measure fair value. The hierarchy is defined as follows: • Level 1 – Quoted prices in active markets for identical assets or liabilities. • Level 2 – Observable inputs other than level 1 prices, such as quoted prices for similar instruments, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data. • Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. These inputs require significant management judgment or estimation, some of which use model-based techniques and may be internally developed. Assets and liabilities are assigned to a level within the fair value hierarchy based on the lowest level of significant input used to measure fair value. Assets and liabilities may change levels within the fair value hierarchy due to market conditions or other circumstances. Those transfers are recognized on the date of the event that prompted the transfer. There were no transfers of assets or liabilities required to be measured at fair value on a recurring basis between levels of the fair value hierarchy during the periods presented. Assets and Liabilities Required to be Measured at Fair Value on a Recurring Basis The following table provides the fair value for assets and liabilities required to be measured at fair value on a recurring basis in the Consolidated Statements of Financial Condition by level in the fair value hierarchy. Recurring Fair Value Measurements (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Trading securities: Money market funds $ 1,685 $ — $ — $ 1,645 $ — $ — Mutual funds 18,762 — — 16,275 — — Total trading securities 20,447 — — 17,920 — — Securities available-for-sale: U.S. treasury securities 46,345 — — 48,541 — — U.S. agency securities — 156,847 — — 183,637 — CMOs — 1,095,186 — — 1,047,446 — MBSs — 369,543 — — 332,655 — Municipal securities — 208,991 — — 270,846 — CDOs — — — — — 33,260 Equity securities — 7,297 — — 3,065 — Total securities available-for-sale 46,345 1,837,864 — 48,541 1,837,649 33,260 Mortgage servicing rights ("MSRs") (1) — — 5,894 — — 6,120 Derivative assets (1) — 21,068 — — 18,880 — Liabilities Derivative liabilities (2) $ — $ 25,250 $ — $ — $ 21,150 $ — (1) Included in other assets in the Consolidated Statements of Financial Condition. (2) Included in other liabilities in the Consolidated Statements of Financial Condition. The following sections describe the specific valuation techniques and inputs used to measure financial assets and liabilities at fair value. Trading Securities The Company's trading securities consist of diversified investment securities held in a grantor trust and are invested in money market and mutual funds. The fair value of these money market and mutual funds is based on quoted market prices in active exchange markets and is classified in level 1 of the fair value hierarchy. Securities Available-for-Sale The Company's securities available-for-sale are primarily fixed income instruments that are not quoted on an exchange, but may be traded in active markets. The fair values for these securities are based on quoted prices in active markets or market prices for similar securities obtained from external pricing services or dealer market participants and are classified in level 2 in the fair value hierarchy. The fair value of U.S. treasury securities is based on quoted market prices in active exchange markets and is classified in level 1 of the fair value hierarchy. Quarterly, the Company evaluates the methodologies used by its external pricing services to estimate the fair value of these securities to determine whether the valuations represent an exit price in the Company's principal markets. CDOs were classified in level 3 in the fair value hierarchy as of December 31, 2016. The Company liquidated all of its remaining CDOs during 2017. The Company estimated the fair values for each CDO using discounted cash flow analyses with the assistance of a structured credit valuation firm. This methodology was based on a credit analysis and historical financial data for each of the issuers underlying the CDOs (the "Issuers"). These estimates are highly subjective and sensitive to several significant, unobservable inputs. The cash flows for each Issuer were then discounted to present values using LIBOR plus an adjustment to reflect the impact of market factors. Finally, the discounted cash flows for each Issuer were aggregated to derive the estimated fair value for the specific CDO. The following table presents the ranges of significant, unobservable inputs calculated using the weighted average of the Issuers used by the Company as of December 31, 2016 . Significant Unobservable Inputs Used in the Valuation of CDOs As of December 31, 2016 Probability of prepayment 0.0 % - 10.9% Probability of default 16.7 % - 46.8% Loss given default 93.3 % - 98.9% Probability of deferral cure 7.6 % - 100.0% The impact of changes in these key inputs could result in a significantly higher or lower fair value measurement for each CDO. The timing of the default, the magnitude of the default, and the timing and magnitude of the cure probability are directly interrelated. Defaults that occur sooner and/or are greater than anticipated have a negative impact on the valuation. In addition, a high cure probability assumption has a positive effect on the fair value, and, if a cure event takes place sooner than anticipated, the impact on the valuation is also favorable. A rollforward of the carrying value of CDOs for the three years ended December 31, 2017 is presented in the following table. Carrying Value of CDOs (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 33,260 $ 31,529 $ 33,774 Additions — — — Change in other comprehensive income (loss) (1) 14,421 2,337 (2,030 ) Paydowns and sales (47,681 ) (606 ) (215 ) Ending balance $ — $ 33,260 $ 31,529 (1) Included in unrealized holding gains (losses) in the Consolidated Statements of Comprehensive Income. Mortgage Servicing Rights The Company services loans for others totaling $607.0 million and $640.5 million as of December 31, 2017 and 2016 , respectively. These loans are owned by third-parties and are not included in the Consolidated Statements of Financial Condition. The Company determines the fair value of MSRs by estimating the present value of expected future cash flows associated with the mortgage loans being serviced and classifies them in level 3 of the fair value hierarchy. The following table presents the ranges of significant, unobservable inputs used by the Company to determine the fair value of MSRs as December 31, 2017 and 2016 . Significant Unobservable Inputs Used in the Valuation of MSRs As of December 31, 2017 2016 Prepayment speed 4.2 % - 13.1% 7.7 % - 22.8% Maturity (months) 6 - 92 12 - 103 Discount rate 9.5 % - 12.0% 9.5 % - 13.0% The impact of changes in these key inputs could result in a significantly higher or lower fair value measurement for MSRs. Significant increases in expected prepayment speeds and discount rates have negative impacts on the valuation. Higher maturity assumptions have a favorable effect on the estimated fair value. A rollforward of the carrying value of MSRs for the three years ended December 31, 2017 is presented in the following table. Carrying Value of MSRs (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 6,120 $ 1,853 $ 1,728 Additions from acquisition — 3,092 — New MSRs 673 1,263 342 Total (losses) gains included in earnings (1) : Changes in valuation inputs and assumptions (41 ) 610 (11 ) Other changes in fair value (2) (858 ) (698 ) (206 ) Ending balance (3) $ 5,894 $ 6,120 $ 1,853 Contractual servicing fees earned during the year (1) $ 1,536 $ 1,312 $ 546 Total amount of loans being serviced for the benefit of others at the end of the year 607,016 640,530 242,915 (1) Included in mortgage banking income in the Consolidated Statements of Income and related to assets held as of December 31, 2017 , 2016 , and 2015 . (2) Primarily represents changes in expected future cash flows over time due to payoffs and paydowns. (3) Included in other assets in the Consolidated Statements of Financial Condition. Derivative Assets and Derivative Liabilities The Company enters into interest rate swaps and derivative transactions with commercial customers. These derivative transactions are executed in the dealer market, and pricing is based on market quotes obtained from the counterparties. The market quotes were developed using market observable inputs, which primarily include LIBOR. Therefore, derivatives are classified in level 2 of the fair value hierarchy. For its derivative assets and liabilities, the Company also considers non-performance risk, including the likelihood of default by itself and its counterparties, when evaluating whether the market quotes from the counterparties are representative of an exit price. Pension Plan Assets Although Pension Plan assets are not consolidated in the Company's Consolidated Statements of Financial Condition, they are required to be measured at fair value on an annual basis. The fair value of Pension Plan assets is presented in the following table by level in the fair value hierarchy. Annual Fair Value Measurements for Pension Plan Assets (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Level 1 Level 2 Total Level 1 Level 2 Total Pension plan assets: Mutual funds (1) $ 41,002 $ — $ 41,002 $ 29,071 $ — $ 29,071 U.S. government and government agency securities 3,678 9,397 13,075 5,957 7,947 13,904 Corporate bonds — 9,171 9,171 — 7,010 7,010 Common stocks — — — 7,526 — 7,526 Common trust funds — 2,911 2,911 — 7,678 7,678 Total pension plan assets $ 44,680 $ 21,479 $ 66,159 $ 42,554 $ 22,635 $ 65,189 (1) Includes mutual funds, money market funds, cash, cash equivalents, and accrued interest. Mutual funds, certain U.S. government agency securities, and common stocks are based on quoted market prices in active exchange markets and classified in level 1 of the fair value hierarchy. Corporate bonds and certain U.S. government and government agency securities are valued at quoted prices from independent sources that are based on observable market trades or observable prices for similar bonds where a price for the identical bond is not observable and, therefore, are classified in level 2 of the fair value hierarchy. Common trust funds are valued at quoted redemption values on the last business day of the Pension Plan's fiscal year and are classified in level 2 of the fair value hierarchy. There were no Pension Plan assets classified in level 3 of the fair value hierarchy. Assets and Liabilities Required to be Measured at Fair Value on a Non-Recurring Basis The following table provides the fair value for each class of assets and liabilities required to be measured at fair value on a non-recurring basis in the Consolidated Statements of Financial Condition by level in the fair value hierarchy. Non-Recurring Fair Value Measurements (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Collateral-dependent impaired loans (1) $ — $ — $ 33,240 $ — $ — $ 22,019 OREO (2) — — 12,340 — — 8,624 Loans held-for-sale (3) — — 21,098 — — 10,484 Assets held-for-sale (4) — — 2,208 — — 4,075 (1) Includes impaired loans with charge-offs and impaired loans with a specific reserve during the periods presented. (2) Includes OREO with fair value adjustments subsequent to initial transfer that occurred during the periods presented. (3) Included in other assets in the Consolidated Statements of Financial Condition. (4) Included in premises, furniture, and equipment in the Consolidated Statements of Financial Condition. Collateral-Dependent Impaired Loans Certain collateral-dependent impaired loans are subject to fair value adjustments to reflect the difference between the carrying value of the loan and the value of the underlying collateral. The fair values of collateral-dependent impaired loans are primarily determined by current appraised values of the underlying collateral. Based on the age and/or type, appraisals may be adjusted in the range of 0% to 15% . In certain cases, an internal valuation may be used when the underlying collateral is located in areas where comparable sales data is limited or unavailable. Accordingly, collateral-dependent impaired loans are classified in level 3 of the fair value hierarchy. Collateral-dependent impaired loans for which the fair value is greater than the recorded investment are not measured at fair value in the Consolidated Statements of Financial Condition and are not included in this disclosure. OREO The fair value of OREO is measured using the current appraised value of the properties. In certain circumstances, a current appraisal may not be available or may not represent an accurate measurement of the property's fair value due to outdated market information or other factors. In these cases, the fair value is determined based on the lower of the (i) most recent appraised value, (ii) broker price opinion, (iii) current listing price, or (iv) signed sales contract. Given these valuation methods, OREO is classified in level 3 of the fair value hierarchy. Loans Held-for-Sale Loans held-for-sale consists of 1-4 family mortgage loans, which were originated with the intent to sell as of December 31, 2017 and 2016 . These loans were recorded in the held-for-sale category at the contract price, which approximates fair value, and, accordingly, are classified in level 3 of the fair value hierarchy. Assets Held-for-Sale As of December 31, 2017 , assets held-for-sale consists of former branches that are no longer in operation and parcels of land previously purchased for expansion. These properties are being actively marketed and were transferred into the held-for-sale category at their fair value, as determined by current appraisals. Based on these valuation methods, they are classified in level 3 of the fair value hierarchy. Goodwill and Other Intangible Assets Goodwill and other intangible assets are subject to annual impairment testing, which requires a significant degree of management judgment. If the testing had resulted in impairment, the Company would have classified goodwill and other intangible assets as a level 3 non-recurring fair value measurement. Additional information regarding goodwill, other intangible assets, and impairment policies can be found in Note 1 , " Summary of Significant Accounting Policies ," and Note 9 , " Goodwill and Other Intangible Assets ." Financial Instruments Not Required to be Measured at Fair Value For certain financial instruments that are not required to be measured at fair value in the Consolidated Statements of Financial Condition, the Company must disclose the estimated fair values and the level within the fair value hierarchy as shown in the following table. Fair Value Measurements of Other Financial Instruments (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Fair Value Hierarchy Carrying Fair Value Carrying Fair Value Assets Cash and due from banks 1 $ 192,800 $ 192,800 $ 155,055 $ 155,055 Interest-bearing deposits in other banks 2 153,770 153,770 107,093 107,093 Securities held-to-maturity 2 13,760 12,013 22,291 18,212 FHLB and FRB stock 2 69,708 69,708 59,131 59,131 Loans 3 10,345,397 10,059,992 8,172,584 7,973,845 Investment in BOLI 3 279,900 279,900 219,746 219,746 Accrued interest receivable 3 45,261 45,261 34,384 34,384 Other interest-earning assets 3 228 228 834 834 Liabilities Deposits 2 $ 11,053,325 $ 11,038,819 $ 8,828,603 $ 8,820,572 Borrowed funds 2 714,884 714,884 879,008 879,008 Senior and subordinated debt 2 195,170 198,806 194,603 197,888 Accrued interest payable 2 4,704 4,704 3,416 3,416 Management uses various methodologies and assumptions to determine the estimated fair values of the financial instruments in the table above. The fair value estimates are made at a discrete point in time based on relevant market information and consider management's judgments regarding future expected economic conditions, loss experience, and specific risk characteristics of the financial instruments. Short-Term Financial Assets and Liabilities – For financial instruments with a shorter-term or with no stated maturity, prevailing market rates, and limited credit risk, the carrying amounts approximate fair value. Those financial instruments include cash and due from banks, interest-bearing deposits in other banks, accrued interest receivable, and accrued interest payable. Securities Held-to-Maturity – The fair value of securities held-to-maturity is estimated using the present value of expected future cash flows of the remaining maturities of the securities. FHLB and FRB Stock – The carrying amounts approximate fair value as the stock is non-marketable. Loans – Loans includes the FDIC indemnification asset and net loans, which consists of loans held-for-investment, acquired loans, and the allowance for loan losses. The fair value of loans is estimated using the present value of the expected future cash flows of the remaining maturities of the loans. Prepayment assumptions that consider the Company's historical experience and current economic and lending conditions were included. The discount rate was based on the LIBOR yield curve with adjustments for liquidity and credit risk inherent in the loans. Investment in BOLI – The fair value of BOLI approximates the carrying amount as both are based on each policy's respective CSV, which is the amount the Company would receive from liquidation of these investments. The CSV is derived from monthly reports provided by the managing brokers and is determined using the Company's initial insurance premium and earnings of the underlying assets, offset by management fees. Other Interest-Earning Assets – The fair value of other interest-earning assets is estimated using the present value of the expected future cash flows of the remaining maturities of the assets. Deposits – The fair values disclosed for demand deposits, savings deposits, NOW accounts, and money market deposits are equal to the amount payable on demand at the reporting date (i.e., their carrying amounts). The fair value for fixed-rate time deposits was estimated using the expected future cash flows discounted based on the LIBOR yield curve, plus or minus the spread associated with current pricing. Borrowed Funds – The fair value of FHLB advances is estimated by discounting the agreements based on maturities using the rates currently offered for FHLB advances of similar remaining maturities adjusted for prepayment penalties that would be incurred if the borrowings were paid off on the measurement date. The carrying amounts of securities sold under agreements to repurchase approximate their fair value due to their short-term nature. Senior and Subordinated Debt – The fair values of senior and subordinated notes are estimated based on quoted market prices of similar instruments. The fair values of junior subordinated debentures are estimated based on quoted market prices of comparable securities when available, or by discounting the expected future cash flows at market interest rates. Commitments to Extend Credit and Letters of Credit – The Company estimated the fair value of lending commitments outstanding to be immaterial based on (i) the limited interest rate exposure of the commitments outstanding due to their variable nature, (ii) the short-term nature of the commitment periods, (iii) termination clauses provided in the agreements, and (iv) the market rate of fees charged.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS The Company, through the Bank, makes loans to and has transactions with certain of its directors and executive officers. All of these loans and transactions were made on substantially the same terms, including interest rates and collateral requirements, for comparable transactions with unrelated persons and did not involve more than the normal risk of collectability or present unfavorable features. For the years ended December 31, 2017 and 2016 , loans to directors and executive officers were not greater than 5% of stockholders' equity.

Condensed Parent Company Financ

Condensed Parent Company Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Parent Company Financial Statements	CONDENSED PARENT COMPANY FINANCIAL STATEMENTS The following represents the condensed financial statements of First Midwest Bancorp, Inc., the Parent Company. Statements of Financial Condition (Parent Company only) (Dollar amounts in thousands) As of December 31, 2017 2016 Assets Cash and due from banks $ 120,812 $ 140,217 Investments in and advances to subsidiaries 1,952,414 1,279,065 Other assets 43,606 139,060 Total assets $ 2,116,832 $ 1,558,342 Liabilities and Stockholders' Equity Senior and subordinated debt $ 195,170 $ 194,603 Accrued interest payable and other liabilities 56,788 106,659 Stockholders' equity 1,864,874 1,257,080 Total liabilities and stockholders' equity $ 2,116,832 $ 1,558,342 Statements of Income (Parent Company only) (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Income Dividends from subsidiaries $ 74,091 $ 86,791 $ 127,000 Interest income 2,211 2,188 2,164 Securities transactions and other (1,372 ) 215 584 Total income 74,930 89,194 129,748 Expenses Interest expense 12,428 12,477 12,545 Salaries and employee benefits 20,978 16,104 14,624 Other expenses 9,126 7,110 6,003 Total expenses 42,532 35,691 33,172 Income before income tax benefit and equity in undistributed income (loss) of subsidiaries 32,398 53,503 96,576 Income tax benefit 14,851 12,878 11,950 Income before equity in undistributed income (loss) of subsidiaries 47,249 66,381 108,526 Equity in undistributed income (loss) of subsidiaries 51,138 25,968 (26,462 ) Net income 98,387 92,349 82,064 Net income applicable to non-vested restricted shares (916 ) (1,043 ) (882 ) Net income applicable to common shares $ 97,471 $ 91,306 $ 81,182 Statements of Cash Flows (Parent Company only) (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Operating Activities Net income $ 98,387 $ 92,349 $ 82,064 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed (income) loss of subsidiaries (51,138 ) (25,968 ) 26,462 Depreciation of premises, furniture, and equipment 9 2 7 Net securities losses (gains) 1,523 — (1 ) Share-based compensation expense 11,223 7,879 7,242 Tax benefit (expense) related to share-based compensation 349 (197 ) (406 ) Net decrease (increase) in other assets 18,667 (75,104 ) 23,699 Net (decrease) increase in other liabilities (52,377 ) 74,571 (17,132 ) Net cash provided by operating activities 26,643 73,532 121,935 Investing Activities Purchases of securities available-for-sale — (14 ) — Proceeds from sales and maturities of securities available-for-sale 42,516 601 310 Purchase of premises, furniture, and equipment (119 ) — (5 ) Net cash paid for acquisitions (47,364 ) (14,905 ) (16,047 ) Net cash used in investing activities (4,967 ) (14,318 ) (15,742 ) Financing Activities Net proceeds from the issuance of subordinated debt — 146,484 — Payments for the retirement of senior and subordinated debt — (153,500 ) — Treasury stock activity — — (120 ) Cash dividends paid (37,129 ) (29,198 ) (27,036 ) Restricted stock activity (3,952 ) (2,476 ) (2,890 ) Net cash used in financing activities (41,081 ) (38,690 ) (30,046 ) Net (decrease) increase in cash and cash equivalents (19,405 ) 20,524 76,147 Cash and cash equivalents at beginning of year 140,217 119,693 43,546 Cash and cash equivalents at end of year $ 120,812 $ 140,217 $ 119,693 Supplemental Disclosures of Cash Flow Information: Common stock issued for acquisitions, net of issuance costs $ 534,090 $ 54,896 $ —

Summary of Significant Accoun33

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Nature of Operations and Basis of Presentation	Nature of Operations – First Midwest Bancorp, Inc. (the "Company") is a bank holding company that was incorporated in Delaware in 1982 and began operations on March 31, 1983. The Company is headquartered in Itasca, Illinois and has operations located primarily throughout the Chicago metropolitan area, as well as northwest Indiana, central and western Illinois, and eastern Iowa. The Company operates three wholly-owned subsidiaries: First Midwest Bank (the "Bank"), Catalyst Asset Holdings, LLC ("Catalyst"), and Premier Asset Management LLC ("Premier"). The Bank conducts the majority of the Company's operations, Catalyst manages certain non-performing assets of the Company, and Premier is a registered investment advisor providing advisory services to certain of the Company's wealth management clients. The Company is engaged in commercial and retail banking and offers a broad range of banking, treasury management, and wealth management products and services, tailored to the needs of its commercial and industrial, commercial real estate, municipal, and consumer customers. Basis of Presentation – The accounting and reporting policies of the Company and its subsidiaries conform to U.S. generally accepted accounting principles ("GAAP") and general practices within the banking industry. The Company uses the accrual basis of accounting for financial reporting purposes.
Reclassification	Certain reclassifications were made to prior year amounts to conform to the current year presentation.
Use of Estimates	Use of Estimates – The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates and assumptions are based on the best available information, actual results could differ from those estimates.
Principles of Consolidation	Principles of Consolidation – The accompanying consolidated financial statements include the financial position and results of operations of the Company and its subsidiaries after elimination of all significant intercompany accounts and transactions. Assets held in a fiduciary or agency capacity are not assets of the Company or its subsidiaries and are not included in the consolidated financial statements.
Segment Disclosures	Segment Disclosures – The Company has one reportable segment. The Company's chief operating decision maker evaluates the operations of the Company using consolidated information for purposes of allocating resources and assessing performance. Therefore, segment disclosures are not required.
Business Combinations	Business Combinations – Business combinations are accounted for under the acquisition method of accounting. Assets acquired and liabilities assumed are recorded at their estimated fair values as of the date of acquisition, with any excess of the purchase price of the acquisition over the fair value of the identifiable net tangible and intangible assets acquired recorded as goodwill. Alternatively, a gain is recorded if the fair value of assets purchased exceeds the fair value of liabilities assumed and consideration paid. The results of operations of the acquired business are included in the Consolidated Statements of Income from the effective date of the acquisition.
Cash and Cash Equivalents	Cash and Cash Equivalents – For purposes of the Consolidated Statements of Cash Flows, management defines cash and cash equivalents to include cash and due from banks, interest-bearing deposits in other banks, and other short-term investments, if any, such as federal funds sold and securities purchased under agreements to resell.
Securities	Securities – Securities are classified as held-to-maturity, trading, or available-for-sale at the time of purchase. Securities Held-to-Maturity – Securities classified as held-to-maturity are securities for which management has the intent and ability to hold to maturity. These securities are stated at cost and adjusted for amortization of premiums and accretion of discounts over the estimated lives of the securities using the effective interest method. Trading Securities – The Company's trading securities consist of diversified investment securities held in a grantor trust under deferred compensation arrangements in which plan participants may direct amounts earned to be invested in securities other than Company stock. The accounts of the grantor trust are consolidated with the accounts of the Company in its consolidated financial statements. Trading securities are reported at fair value. Other than the securities held in the grantor trust, the Company does not carry any securities for trading purposes. Securities Available-for-Sale – All other securities are classified as available-for-sale. Securities available-for-sale are carried at fair value with unrealized gains and losses, net of related deferred income taxes, recorded in stockholders' equity as a separate component of accumulated other comprehensive loss. The historical cost of debt securities is adjusted for amortization of premiums and accretion of discounts over the estimated life of the security using the effective interest method. Amortization of premiums and accretion of discounts are included in interest income. Purchases and sales of securities are recognized on a trade date basis. Realized securities gains or losses are reported in net securities (losses) gains in the Consolidated Statements of Income. The cost of securities sold is based on the specific identification method. On a quarterly basis, the Company individually assesses securities with unrealized losses to determine whether there were any events or circumstances indicating that an other-than-temporary impairment ("OTTI") has occurred. In evaluating OTTI, the Company considers many factors, including (i) the severity and duration of the impairment, (ii) the financial condition and near-term prospects of the issuer, including external credit ratings and recent downgrades for debt securities, (iii) its intent to hold the security until its value recovers, and (iv) the likelihood that it will be required to sell the security before a recovery in value, which may be at maturity. If management intends to sell the security or believes it is more likely than not that it will be required to sell the security prior to full recovery, an OTTI charge will be recognized through income as a realized loss and included in net securities (losses) gains in the Consolidated Statements of Income. If management does not expect to sell the security or believes it is not more likely than not that it will be required to sell the security prior to full recovery, the OTTI is separated into the amount related to credit deterioration, which is recognized through income as a realized loss, and the amount resulting from other factors, which is recognized in other comprehensive income (loss).
FHLB and FRB Stock	FHLB and FRB Stock – The Company, as a member of the FHLB and FRB, is required to maintain an investment in the capital stock of the FHLB and FRB. No ready market exists for these stocks, and they have no quoted market values. The stock is redeemable at par by the FHLB and FRB and is, therefore, carried at cost and periodically evaluated for impairment.
Loans	Loans – Loans held-for-investment are loans that the Company intends to hold until they are paid in full and are carried at the principal amount outstanding, including certain net deferred loan origination fees. Loan origination fees, commitment fees, and certain direct loan origination costs are deferred, and the net amount is amortized as a yield adjustment over the contractual life of the related loans or commitments and included in interest income. Fees related to letters of credit are amortized into fee income over the contractual life of the commitment. Other credit-related fees are recognized as fee income when earned. The Company's net investment in direct financing leases is included in loans and consists of future minimum lease payments and estimated residual values, net of unearned income. Interest income on loans is accrued based on principal amounts outstanding. Loans held-for-sale are carried at the lower of aggregate cost or fair value and included in other assets in the Consolidated Statements of Financial Condition.
Acquired and Covered Loans	Acquired and Covered Loans – Covered loans consist of loans acquired by the Company in FDIC-assisted transactions, which are covered by loss share agreements with the FDIC (the "FDIC Agreements"), under which the FDIC reimburses the Company for the majority of the losses and eligible expenses related to these assets during the coverage period. Acquired loans consist of all other loans that were acquired in business combinations that are not covered by the FDIC Agreements. Certain loans that were previously classified as covered loans are no longer covered under the FDIC Agreements, and are included in acquired loans. Covered loans and acquired loans are included within loans held-for-investment. Acquired and covered loans are separated into (i) non-purchased credit impaired ("non-PCI") and (ii) purchased credit impaired ("PCI") loans. Non-PCI loans include loans that did not have evidence of credit deterioration since origination at the acquisition date. PCI loans include loans that had evidence of credit deterioration since origination and for which it was probable at acquisition that the Company would not collect all contractually required principal and interest payments. Evidence of credit deterioration was evaluated using various indicators, such as past due and non-accrual status. Leases and revolving loans do not qualify to be accounted for as PCI loans and are accounted for as non-PCI loans. The acquisition adjustment related to non-PCI loans is amortized into interest income over the contractual life of the related loans. If an acquired non-PCI loan is renewed subsequent to the acquisition date, any remaining acquisition adjustment is accreted into interest income and the loan is considered a new loan that is no longer classified as an acquired loan. PCI loans are accounted for based on estimates of expected future cash flows. To estimate the fair value, the Company generally aggregates purchased consumer loans and commercial loans into pools of loans with common risk characteristics, such as delinquency status, credit score, and internal risk ratings. The fair values of larger balance commercial loans are estimated on an individual basis. Expected future cash flows in excess of the fair value of loans at the purchase date ("accretable yield") are recorded as interest income over the life of the loans if the timing and amount of the expected future cash flows can be reasonably estimated. The non-accretable yield represents the difference between contractually required payments and the expected future cash flows determined at acquisition. Subsequent increases in expected future cash flows are offset against the allowance for credit losses to the extent an allowance has been established or otherwise recognized as interest income prospectively. The present value of any decreases in expected future cash flows is recognized by recording a charge-off through the allowance for loan losses or providing an allowance for loan losses.
90-Days Past Due Loans	90-Days Past Due Loans – The Company's accrual of interest on loans is generally discontinued at the time the loan is 90 days past due unless the credit is sufficiently collateralized and in the process of renewal or collection.
Non-accrual Loans	Non-accrual Loans – Generally, corporate loans are placed on non-accrual status (i) when either principal or interest payments become 90 days or more past due unless the credit is sufficiently collateralized and in the process of renewal or collection or (ii) when an individual analysis of a borrower's creditworthiness warrants a downgrade to non-accrual regardless of past due status. When a loan is placed on non-accrual status, unpaid interest credited to income in the current year is reversed, and unpaid interest accrued in prior years is charged against the allowance for loan losses. After the loan is placed on non-accrual status, all debt service payments are applied to the principal on the loan. Future interest income may only be recorded on a cash basis after recovery of principal is reasonably assured. Non-accrual loans are returned to accrual status when the financial position of the borrower and other relevant factors indicate that the Company will collect all principal and interest. Commercial loans and loans secured by real estate are charged-off when deemed uncollectible. A loss is recorded if the net realizable value of the underlying collateral is less than the outstanding principal and interest. Consumer loans that are not secured by real estate are subject to mandatory charge-off at a specified delinquency date and are usually not classified as non-accrual prior to being charged-off. Closed-end consumer loans, which include installment, automobile, and single payment loans, are usually charged-off no later than the end of the month in which the loan becomes 120 days past due. PCI loans are generally considered accruing loans unless reasonable estimates of the timing and amount of expected future cash flows cannot be determined. Loans without reasonable future cash flow estimates are classified as non-accrual loans, and interest income is not recognized on those loans until the timing and amount of the expected future cash flows can be reasonably determined.
Troubled Debt Restructurings (TDRs)	Troubled Debt Restructurings ("TDRs") – A restructuring is considered a TDR when (i) the borrower is experiencing financial difficulties, and (ii) the creditor grants a concession, such as forgiveness of principal, reduction of the interest rate, changes in payments, or extension of the maturity date. Loans are not classified as TDRs when the modification is short-term or results in an insignificant delay in payments. The Company's TDRs are determined on a case-by-case basis. The Company does not accrue interest on a TDR unless it believes collection of all principal and interest under the modified terms is reasonably assured. For a TDR to begin accruing interest, the borrower must demonstrate some level of past performance and the future capacity to perform under the modified terms. Generally, six months of consecutive payment performance under the restructured terms is required before a TDR is returned to accrual status. However, the period could vary depending on the individual facts and circumstances of the loan. An evaluation of the borrower's current creditworthiness is used to assess the borrower's capacity to repay the loan under the modified terms. This evaluation includes an estimate of expected future cash flows, evidence of strong financial position, and estimates of the value of collateral, if applicable. For TDRs to be removed from TDR status in the calendar year after the restructuring, the loans must (i) have an interest rate and terms that reflect market conditions at the time of restructuring, and (ii) be in compliance with the modified terms. If the loan was restructured at below market rates and terms, it continues to be separately reported as a TDR until it is paid in full or charged-off.
Impaired Loans	Impaired Loans – Impaired loans consist of corporate non-accrual loans and TDRs. A loan is considered impaired when it is probable that the Company will not collect all contractual principal and interest. With the exception of accruing TDRs, impaired loans are classified as non-accrual and are exclusive of smaller homogeneous loans, such as home equity, 1-4 family mortgages, and installment loans. Impaired loans with balances under a specified threshold are not individually evaluated for impairment. For all other impaired loans, impairment is measured by comparing the estimated value of the loan to the recorded book value. The value of collateral-dependent loans is based on the fair value of the underlying collateral, less costs to sell. The value of other loans is measured using the present value of expected future cash flows discounted at the loan's initial effective interest rate.
Allowance for Credit Losses	Allowance for Credit Losses – The allowance for credit losses is comprised of the allowance for loan losses and the reserve for unfunded commitments, and is maintained by management at a level believed adequate to absorb estimated losses inherent in the existing loan portfolio. Determination of the allowance for credit losses is subjective since it requires significant estimates and management judgment, including the amounts and timing of expected future cash flows on impaired loans, estimated losses on pools of homogeneous loans, consideration of current economic trends, and other factors. Loans deemed to be uncollectible are charged-off against the allowance for loan losses, while recoveries of amounts previously charged-off are credited to the allowance for loan losses. Additions to the allowance for loan losses are charged to expense through the provision for loan losses. The amount of provision depends on a number of factors, including net charge-off levels, loan growth, changes in the composition of the loan portfolio, and the Company's assessment of the allowance for loan losses based on the methodology discussed below. Allowance for Loan Losses – The allowance for loan losses consists of (i) specific reserves for individual loans where the recorded investment exceeds the value, (ii) an allowance based on a loss migration analysis that uses historical credit loss experience for each loan category, and (iii) an allowance based on other internal and external qualitative factors. The specific reserves component of the allowance for loan losses is based on a periodic analysis of impaired loans exceeding a fixed dollar amount. If the value of an impaired loan is less than the recorded book value, the Company either establishes a valuation allowance (i.e., a specific reserve) equal to the excess of the book value over the collateral value of the loan as a component of the allowance for loan losses or charges off the amount if it is a confirmed loss. The general reserve component is based on a loss migration analysis, which examines actual loss experience by loan category for a rolling 8-quarter period and the related internal risk rating for corporate loans. The loss migration analysis is updated quarterly primarily using actual loss experience. This component is then adjusted based on management's consideration of many internal and external qualitative factors, including: • Changes in the composition of the loan portfolio, trends in the volume of loans, and trends in delinquent and non-accrual loans that could indicate that historical trends do not reflect current conditions. • Changes in credit policies and procedures, such as underwriting standards and collection, charge-off, and recovery practices. • Changes in the experience, ability, and depth of credit management and other relevant staff. • Changes in the quality of the Company's loan review system and Board of Directors oversight. • The effect of any concentration of credit and changes in the level of concentrations, such as loan type or risk rating. • Changes in the value of the underlying collateral for collateral-dependent loans. • Changes in the national and local economy that affect the collectability of various segments of the portfolio. • The effect of other external factors, such as competition and legal and regulatory requirements, on the Company's loan portfolio. The allowance for loan losses also consists of an allowance on acquired and covered non-PCI and PCI loans. No allowance for loan losses is recorded on acquired loans at the acquisition date. Subsequent to the acquisition date, an allowance for credit losses is established as necessary to reflect credit deterioration. The acquired non-PCI allowance is based on management's evaluation of the acquired non-PCI loan portfolio giving consideration to the current portfolio balance including the remaining acquisition adjustments, maturity dates, and overall credit quality. The allowance for covered non-PCI loans is calculated in the same manner as the general reserve component based on a loss migration analysis as discussed above. The acquired and covered PCI allowance reflects the difference between the carrying value and the discounted expected future cash flows of the acquired and covered PCI loans. On a periodic basis, the adequacy of this allowance is determined through a re-estimation of expected future cash flows on all of the outstanding acquired and covered PCI loans using either a probability of default/loss given default ("PD/LGD") methodology or a specific review methodology. The PD/LGD model is a loss model that estimates expected future cash flows using a probability of default curve and loss given default estimates. Acquired non-PCI loans that have renewed subsequent to the respective acquisition dates are no longer classified as acquired loans. Instead, they are included in the general loan population and allocated an allowance based on a loss migration analysis. Reserve for Unfunded Commitments – The Company also maintains a reserve for unfunded commitments, including letters of credit, for the risk of loss inherent in these arrangements. The reserve for unfunded commitments is estimated using the loss migration analysis from the allowance for loan losses, adjusted for probabilities of future funding requirements. The reserve for unfunded commitments is included in other liabilities in the Consolidated Statements of Financial Condition. The establishment of the allowance for credit losses involves a high degree of judgment given the difficulty of assessing the factors impacting loan repayment and estimating the timing and amount of losses. While management utilizes its best judgment and information available, the adequacy of the allowance for credit losses depends on a variety of factors beyond the Company's control, including the performance of its loan portfolio, the economy, changes in interest rates and property values, and the interpretation of loan risk classifications by regulatory authorities.
OREO	OREO – OREO consists of properties acquired through foreclosure in partial or total satisfaction of defaulted loans. At initial transfer into OREO, properties are recorded at fair value, less estimated selling costs. Subsequently, OREO is carried at the lower of the cost basis or fair value, less estimated selling costs. OREO write-downs occurring at the transfer date are charged against the allowance for loan losses, establishing a new cost basis. Subsequent to the initial transfer, the carrying values of OREO may be adjusted through a valuation allowance to reflect reductions in value resulting from new appraisals, new list prices, changes in market conditions, or changes in disposition strategies. Increases in value can be recognized through a reduction in the valuation allowance, but may not exceed the established cost basis. These valuation adjustments, along with expenses related to maintenance of the properties, are included in net OREO expense in the Consolidated Statements of Income.
FDIC Indemnification Asset	FDIC Indemnification Asset – The majority of loans and OREO acquired through FDIC-assisted transactions are covered by the FDIC Agreements, under which the FDIC reimburses the Company for the majority of the losses and eligible expenses related to these assets during the coverage period. The FDIC indemnification asset represents the present value of expected future reimbursements from the FDIC. Since the indemnified items are covered loans and covered OREO, which are initially measured at fair value, the FDIC indemnification asset is also initially measured at fair value by discounting the expected future cash flows to be received from the FDIC. These expected future cash flows are estimated by multiplying estimated losses on covered PCI loans and covered OREO by the reimbursement rates in the FDIC Agreements. The balance of the FDIC indemnification asset is adjusted periodically to reflect changes in expected future cash flows. Decreases in estimated reimbursements from the FDIC are recorded prospectively through amortization and increases in estimated reimbursements from the FDIC are recognized by an increase in the carrying value of the indemnification asset. Payments from the FDIC for reimbursement of losses result in a reduction of the FDIC indemnification asset.
Depreciable Assets	Depreciable Assets – Premises, furniture, and equipment are stated at cost, less accumulated depreciation. Depreciation expense is determined by the straight-line method over the estimated useful lives of the assets. Useful lives range from 3 to 10 years for furniture and equipment and 25 to 40 years for premises. Leasehold improvements are amortized over the shorter of the life of the asset or the lease term. Gains on dispositions are included in other noninterest income and losses on dispositions are included in other noninterest expense in the Consolidated Statements of Income. Maintenance and repairs are charged to operating expenses as incurred, while improvements that extend the useful life of assets are capitalized and depreciated over the estimated remaining life. Certain assets, such as buildings and land, that the Company intends to sell and meet held-for-sale criteria are transferred into the held-for-sale category at the lower of their fair value, as determined by a current appraisal, or their recorded investment. Long-lived depreciable assets are evaluated periodically for impairment when events or changes in circumstances indicate the carrying amount may not be recoverable. Impairment exists when the undiscounted expected future cash flows of a long-lived asset are less than its carrying value. In that event, the Company recognizes a loss for the difference between the carrying amount and the estimated fair value of the asset based on a quoted market price, if applicable, or a discounted cash flow analysis. Impairment losses are recorded in other noninterest expense in the Consolidated Statements of Income.
BOLI	BOLI – BOLI represents life insurance policies on the lives of certain Company directors and officers for which the Company is the sole owner and beneficiary. These policies are recorded as an asset in the Consolidated Statements of Financial Condition at their cash surrender value ("CSV") or the current amount that could be realized if settled. The change in CSV and insurance proceeds received are included as a component of noninterest income in the Consolidated Statements of Income.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets – Goodwill represents the excess of the purchase price of the acquisition over the fair value of the net tangible and intangible assets acquired using the acquisition method of accounting. Goodwill is not amortized. Instead, impairment testing is conducted annually as of October 1 or more often if events or circumstances between annual tests indicate that there may be impairment. Impairment testing is performed using either a qualitative or quantitative approach at the reporting unit level. All of the Company's goodwill is allocated to First Midwest Bancorp, Inc., which is the Company's only applicable reporting unit for purposes of testing goodwill for impairment. The Company performs impairment testing using a qualitative approach to determine whether it is more-likely-than-not that the fair value of a reporting unit is less than its carrying amount. Qualitative factors include, but are not limited to, macroeconomic conditions, industry and market specific conditions and trends, the Company's financial performance, market capitalization, stock price, and Company-specific events relevant to the assessment. If the assessment of qualitative factors indicates that it is not more-likely-than-not that an impairment exists, no further testing is performed; otherwise, the Company would proceed with a quantitative two-step goodwill impairment test. In the first step, the Company compares its estimate of the fair value of the reporting unit, which is based on a discounted cash flow analysis, with its carrying amount, including goodwill. If the fair value of the reporting unit exceeds its carrying amount, goodwill of the reporting unit is not impaired and the second step is not required. If necessary, the second step compares the implied fair value of the reporting unit goodwill with the carrying amount of that goodwill. The implied fair value of goodwill is determined by assigning the value of the reporting unit to all of the assets and liabilities of that unit, including any other identifiable intangible assets. An impairment loss is recognized if the carrying amount of the reporting unit goodwill exceeds the implied fair value of goodwill. Other intangible assets represent purchased assets that lack physical substance, but can be distinguished from goodwill because of contractual or other legal rights or because the asset is capable of being sold or exchanged either on its own or in combination with a related contract, asset, or liability. Identified intangible assets that have a finite useful life are amortized over that life in a manner that reflects the estimated decline in the economic value of the identified intangible asset. All of the Company's other intangible assets have finite lives and are amortized over varying periods not exceeding 13 years. Intangible assets are reviewed for impairment annually or more frequently when events or circumstances indicate that its carrying amount may not be recoverable.
Wealth Management	Wealth Management – Assets held in a fiduciary or agency capacity for customers are not included in the consolidated financial statements as they are not assets of the Company or its subsidiaries. Fee income is recognized on an accrual basis and is included as a component of noninterest income in the Consolidated Statements of Income.
Derivative Financial Instruments	Derivative Financial Instruments – To provide derivative products to customers and in the ordinary course of business, the Company enters into derivative transactions as part of its overall interest rate risk management strategy to minimize significant unplanned fluctuations in earnings and expected future cash flows caused by interest rate volatility. All derivative instruments are recorded at fair value as either other assets or other liabilities in the Consolidated Statements of Financial Condition. Subsequent changes in a derivative's fair value are recognized in earnings unless specific hedge accounting criteria are met. On the date the Company enters into a derivative contract, the derivative is designated as a fair value hedge, a cash flow hedge, or a non-hedge derivative instrument. Fair value hedges are designed to mitigate exposure to changes in the fair value of an asset or liability attributable to a particular risk, such as interest rate risk. Cash flow hedges are designed to mitigate exposure to variability in expected future cash flows to be received or paid related to an asset, liability, or other type of forecasted transaction. The Company formally documents all relationships between hedging instruments and hedged items, including its risk management objective and strategy at inception. At the hedge's inception and quarterly thereafter, a formal assessment is performed to determine the effectiveness of the derivative in offsetting changes in the fair values or expected future cash flows of the hedged items in the current period and prospectively. If a derivative instrument designated as a hedge is terminated or ceases to be highly effective, hedge accounting is discontinued prospectively, and the gain or loss is amortized into earnings. For fair value hedges, the gain or loss is amortized over the remaining life of the hedged asset or liability. For cash flow hedges, the gain or loss is amortized over the same period that the forecasted hedged transactions impact earnings. If the hedged item is disposed of, any fair value adjustments are included in the gain or loss from the disposition of the hedged item. If the forecasted transaction is no longer probable, the gain or loss is included in earnings immediately. For fair value hedges, changes in the fair value of the derivative instruments, as well as changes in the fair value of the hedged item, are recognized in earnings. For cash flow hedges, the effective portion of the change in fair value of the derivative instrument is reported as a component of accumulated other comprehensive loss and is reclassified to earnings when the hedged transaction is reflected in earnings. Ineffectiveness is calculated based on the change in fair value of the hedged item compared with the change in fair value of the hedging instrument. For all types of hedges, any ineffectiveness in the hedging relationship is recognized in earnings during the period the ineffectiveness occurs.
Comprehensive Income	Comprehensive Income – Comprehensive income is the total of reported net income and other comprehensive income (loss) which includes all other revenues, expenses, gains, and losses that are not reported in net income under GAAP. The Company includes the following items, net of tax, in other comprehensive income (loss) in the Consolidated Statements of Comprehensive Income: (i) changes in unrealized gains or losses on securities available-for-sale, (ii) changes in the fair value of derivatives designated as cash flow hedges, and (iii) changes in unrecognized net pension costs related to the Company's pension plan.
Treasury Stock	Treasury Stock – Treasury stock acquired is recorded at cost and is carried as a reduction of stockholders' equity in the Consolidated Statements of Financial Condition. Treasury stock issued is valued based on the "last in, first out" inventory method. The difference between the consideration received on issuance and the carrying value is charged or credited to additional paid-in capital.
Share-Based Compensation	Share-Based Compensation – The Company recognizes share-based compensation expense based on the estimated fair value of the award at the grant or modification date over the period during which an employee is required to provide service in exchange for such award. Share-based compensation expense is included in salaries and wages in the Consolidated Statements of Income.
Income Taxes	Income Taxes – The Company files United States ("U.S.") federal income tax returns and state income tax returns in various states. The provision for income taxes is based on income in the consolidated financial statements, rather than amounts reported on the Company's income tax return. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis. Deferred tax assets and liabilities are measured using the enacted tax rates that are expected to apply to taxable income in years in which those temporary differences are expected to be recovered or settled. A valuation allowance is established for any deferred tax asset for which recovery or settlement is not more-likely-than-not. The effect of a change in tax rates on deferred tax assets and liabilities is recognized as income or expense in the period that includes the enactment date.
Earnings per Common Share (EPS)	Earnings per Common Share ("EPS") – EPS is computed using the two-class method. Basic EPS is computed by dividing net income applicable to common shares by the weighted-average number of common shares outstanding during the applicable period, excluding outstanding participating securities. Participating securities include non-vested restricted stock awards and restricted stock units, which contain nonforfeitable rights to dividends or dividend equivalents. Diluted earnings per common share is computed using the weighted-average number of shares determined for the basic earnings per common share computation plus the dilutive effect of stock compensation using the treasury stock method.
Adopted Accounting Pronouncements and Accounting Pronouncements Pending Adoption	Adopted Accounting Pronouncements Contingent Put and Call Options in Debt Instruments: In March of 2016, the Financial Accounting Standards Board ("FASB") issued final guidance clarifying the requirements for assessing whether contingent call (put) options that can accelerate the payment of principal on debt instruments are clearly and closely related to their debt hosts. Entities are required to apply the guidance to existing debt instruments (or hybrid financial instruments that are determined to have a debt host) using a modified retrospective transition method as of the period of adoption. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity. Equity Method Accounting: In March of 2016, the FASB issued final guidance to simplify the equity method of accounting. The guidance eliminates the requirement to retrospectively apply equity method accounting in previous periods when an investor initially obtains significant influence over an investee. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity. Accounting for Employee Share-based Payments: In March of 2016, the FASB issued guidance to simplify the accounting for employee share-based payment transactions. The guidance requires entities to recognize the income tax effects of awards in the income statement when the awards vest or are settled. In addition, the guidance allows entities to repurchase more of an employee's shares than it can under current guidance for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. The adoption of this guidance on January 1, 2017 resulted in a $638,000 tax benefit to the provision for income tax expense for the year ended December 31, 2017 , recorded in the Company's results of operations. The Company elected to estimate forfeitures, which is consistent with the Company's practice before the adoption of this guidance. Accounting Pronouncements Pending Adoption Revenue from Contracts with Customers: In May of 2014, the FASB issued guidance that requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In March of 2016, the FASB issued an amendment to this guidance to clarify the implementation of guidance on principal versus agent consideration. Additional amendments to clarify the implementation guidance on the identification of performance obligations and licensing were issued in April of 2016 and narrow-scope improvements and practical expedients were issued in May of 2016. The guidance was initially effective for annual and interim reporting periods beginning on or after December 15, 2016 but was deferred to December 15, 2017, and must be applied either retrospectively or using the modified retrospective approach. Early adoption is permitted, but not before the original effective date. The Company's revenue is comprised of net interest income on financial assets and liabilities, which is excluded from the scope of this guidance, and noninterest income. The primary sources of revenue within noninterest income are service charges on deposit accounts, wealth management fees, card-based fees, and merchant servicing fees. Based upon the Company's final assessment, this guidance will affect the presentation of merchant servicing fees, card-based fees, cardholder expenses, and merchant card expense that are currently presented on a gross basis within noninterest income and noninterest expense but will now be required to be presented on a net basis within noninterest income. In addition, qualitative disclosures regarding noninterest income will be expanded. The Company will adopt this guidance on January 1, 2018 using the modified retrospective approach and does not expect the changes in presentation of certain contract costs or the expanded disclosures to have a significant impact on the Company's financial condition, results of operations, or liquidity. Amendments to Guidance on Classifying and Measuring Financial Instruments: In January of 2016, the FASB issued guidance that will require entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value. Any changes in fair value will be recognized in net income unless the investments qualify for a new practicability exception. This guidance also requires entities to adjust the fair value disclosures for financial instruments carried at amortized cost from an entry price to an exit price. No changes were made to the guidance for classifying and measuring investments in debt securities and loans. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Leases: In February of 2016, the FASB issued guidance to increase transparency and comparability across entities for leasing arrangements. This guidance requires lessees to recognize assets and liabilities for most leases. For lessors, this guidance modifies the lease classification criteria and the accounting for sales-type and direct financing leases. In addition, this guidance clarifies criteria for the determination of whether a contract is or contains a lease. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. During 2016, the Bank entered into a sale-leaseback transaction that resulted in a deferred gain of $82.5 million , with $74.6 million remaining as of December 31, 2017 . Upon adoption of this guidance, the remaining deferred gain will be recognized immediately as a cumulative-effect adjustment to equity and will no longer be accreted as a reduction to lease expense in net occupancy and equipment expense. For additional discussion of the sale-leaseback transaction, see note 8 " Premises, Furniture, and Equipment ." Management is evaluating the new guidance and the additional impact to the Company's financial condition, results of operations, or liquidity. Measurement of Credit Losses on Financial Instruments: In June of 2016, the FASB issued guidance that will require entities to present financial assets measured at amortized cost at the net amount expected to be collected, considering an entity's current estimate of all expected credit losses. In addition, credit losses relating to available-for-sale debt securities will be required to be recorded through an allowance for credit losses, with changes in credit loss estimates recognized through current earnings. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted, but not for periods beginning before December 15, 2018. Management is evaluating the new guidance and the impact to the Company's financial condition, results of operations, and liquidity. Classification of Certain Cash Receipts and Cash Payments: In August of 2016, the FASB issued guidance clarifying certain cash flow presentation and classification issues to reduce diversity in practice. This guidance is effective for annual and interim reporting periods beginning on or after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's Consolidated Statement of Cash Flows. Income Taxes: In October of 2016, the FASB issued guidance that requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Clarifying the Definition of a Business: In January of 2017, the FASB issued guidance that clarifies the definition of a business to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Accounting for Goodwill Impairment: In January of 2017, the FASB issued guidance that simplifies the accounting for goodwill impairment for all entities. The new guidance eliminates the requirement to calculate the implied fair value of goodwill using the second step of the quantitative two-step goodwill impairment model prescribed under current accounting guidance. Under the new guidance, if a reporting unit's carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. This guidance is effective for annual and interim goodwill impairment testing dates beginning after December 15, 2019. Early adoption is permitted for annual and interim goodwill impairment testing dates after January 1, 2017. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Presentation of Defined Benefit Retirement Plan Costs: In March of 2017, the FASB issued guidance that changes how employers that sponsor defined pension and or other postretirement benefit plans present the net periodic benefit cost in the income statement. Employers will present the service cost component of net periodic benefit cost in the same income statement line item as other employee compensation costs arising from services rendered during the period. Other components of net periodic benefit cost will be presented separately from the line item(s) that includes the service cost. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Premium Amortization on Purchased Callable Debt Securities: In March of 2017, the FASB issued guidance that shortens the amortization period for the premium on certain purchased callable debt securities to the earliest call date. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Share-based Payment Award Modifications: In May of 2017, the FASB issued guidance to reduce diversity in practice by clarifying when changes to the terms or conditions of a share-based payment award must be accounted for as a modification. This guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Derivatives and Hedging: In August of 2017, the FASB issued guidance to better align the financial reporting related to hedging activities with the economic objectives of those activities and to simplify the application of current hedge accounting guidance. Entities are required to apply the guidance using a modified retrospective method as of the period of adoption. This guidance is effective for annual and interim periods beginning after December 31, 2018. Early adoption is permitted. Management is evaluating the new guidance, but does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income: In February of 2018, the FASB issued guidance that requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 . Entities electing the reclassification are required to apply the guidance either at the beginning of the period of adoption or retrospectively for all periods impacted. This guidance is effective for annual and interim periods beginning after December 31, 2018. Early adoption is permitted. The Company has elected to reclassify $6.9 million of these stranded tax effects from accumulated other comprehensive loss to retained earnings as of the beginning of the period of adoption on January 1, 2018.
Pension and Other Postretirement Plans	To the extent the cumulative actuarial losses included in accumulated other comprehensive loss exceed 10% of the greater of the accumulated benefit obligation or the market-related value of the Pension Plan assets, it is the Company's policy to amortize the Pension Plan's net actuarial losses into income over the average remaining life expectancy of the Pension Plan participants. Actuarial losses included in accumulated other comprehensive loss as of December 31, 2017 exceeded 10% of the accumulated benefit obligation and the fair value of Pension Plan assets. The amortization of net actuarial losses is a component of the net periodic benefit cost. Amortization of the net actuarial losses and prior service cost included in other comprehensive income (loss) is not expected to have a material impact on the Company's future results of operations, financial position, or liquidity.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Acquisition Activity	The following table presents the assets acquired and liabilities assumed, net of the fair value adjustments, in the Standard and NI Bancshares transactions as of the acquisition date. The assets acquired and liabilities assumed, both intangible and tangible, were recorded at their estimated fair values as of the acquisition date and have been accounted for under the acquisition method of accounting. Acquisition Activity (Dollar amounts in thousands, except share and per share data) Standard NI Bancshares January 6, 2017 March 8, 2016 Assets Cash and due from banks and interest-bearing deposits in other banks $ 102,149 $ 72,533 Securities available-for-sale 214,107 125,843 Securities held-to-maturity — 1,864 FHLB and FRB stock 3,247 1,549 Loans 1,762,303 396,181 OREO 8,424 2,863 Investment in BOLI 55,629 8,384 Goodwill 345,334 22,174 Other intangible assets 31,072 10,408 Premises, furniture, and equipment 56,517 19,636 Accrued interest receivable and other assets 60,278 16,453 Total assets $ 2,639,060 $ 677,888 Liabilities Noninterest-bearing deposits $ 675,354 $ 130,909 Interest-bearing deposits 1,348,520 464,012 Total deposits 2,023,874 594,921 Borrowed funds — 2,416 Intangible liabilities — 230 Accrued interest payable and other liabilities 34,471 10,239 Total liabilities 2,058,345 607,806 Consideration Paid Common stock (2017 - 21,057,085 share issued at $25.34 per share, 2016 - 3,042,494 shares issued at $18.059 per share), net of issuance costs 533,590 54,896 Cash paid 47,125 15,186 Total consideration paid 580,715 70,082 $ 2,639,060 $ 677,888
Unaudited Pro Forma Combined Results of Operations	Unaudited Pro Forma Combined Results of Operations (Dollar amounts in thousands) Years Ended December 31, 2017 2016 Total revenues (1) $ 636,762 $ 616,922 Net income 109,195 108,770 (1) Includes net interest income and total noninterest income.
Summary of Standard Acquired Loans	The following table presents additional detail for loans acquired in the Standard transaction at the acquisition date. Standard Acquired Loans (Dollar amounts in thousands) January 6, 2017 PCI Loans Non-PCI Loans Fair value $ 125,382 $ 1,636,921 Contractually required principal and interest payments 218,680 1,930,311 Best estimate of contractual cash flows not expected to be collected (1) 65,610 100,469 Best estimate of contractual cash flows expected to be collected 153,070 1,829,842 (1) Includes interest payments not expected to be collected due to loan prepayments as well as principal and interest payments not expected to be collected due to customer default.

Securities (Tables)

Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Securities Available-for-Sale	A summary of the Company's securities portfolio by category and maturity is presented in the following tables. Securities Portfolio (Dollar amounts in thousands) As of December 31, 2017 2016 Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Fair Gains Losses Gains Losses Securities Available-for-Sale U.S. treasury securities $ 46,529 $ — $ (184 ) $ 46,345 $ 48,581 $ 26 $ (66 ) $ 48,541 U.S. agency securities 157,636 197 (986 ) 156,847 183,528 519 (410 ) 183,637 Collateralized mortgage 1,113,019 121 (17,954 ) 1,095,186 1,064,130 969 (17,653 ) 1,047,446 Other mortgage-backed 373,676 201 (4,334 ) 369,543 337,139 1,395 (5,879 ) 332,655 Municipal securities 209,558 693 (1,260 ) 208,991 273,319 1,245 (3,718 ) 270,846 Trust-preferred collateralized debt obligations ("CDOs") — — — — 47,681 261 (14,682 ) 33,260 Equity securities 7,408 194 (305 ) 7,297 3,206 147 (288 ) 3,065 Total securities available-for-sale $ 1,907,826 $ 1,406 $ (25,023 ) $ 1,884,209 $ 1,957,584 $ 4,562 $ (42,696 ) $ 1,919,450 Securities Held-to-Maturity Municipal securities $ 13,760 $ — $ (1,747 ) $ 12,013 $ 22,291 $ — $ (4,079 ) $ 18,212 Trading Securities $ 20,447 $ 17,920
Securities Held-to-Maturity	A summary of the Company's securities portfolio by category and maturity is presented in the following tables. Securities Portfolio (Dollar amounts in thousands) As of December 31, 2017 2016 Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Fair Gains Losses Gains Losses Securities Available-for-Sale U.S. treasury securities $ 46,529 $ — $ (184 ) $ 46,345 $ 48,581 $ 26 $ (66 ) $ 48,541 U.S. agency securities 157,636 197 (986 ) 156,847 183,528 519 (410 ) 183,637 Collateralized mortgage 1,113,019 121 (17,954 ) 1,095,186 1,064,130 969 (17,653 ) 1,047,446 Other mortgage-backed 373,676 201 (4,334 ) 369,543 337,139 1,395 (5,879 ) 332,655 Municipal securities 209,558 693 (1,260 ) 208,991 273,319 1,245 (3,718 ) 270,846 Trust-preferred collateralized debt obligations ("CDOs") — — — — 47,681 261 (14,682 ) 33,260 Equity securities 7,408 194 (305 ) 7,297 3,206 147 (288 ) 3,065 Total securities available-for-sale $ 1,907,826 $ 1,406 $ (25,023 ) $ 1,884,209 $ 1,957,584 $ 4,562 $ (42,696 ) $ 1,919,450 Securities Held-to-Maturity Municipal securities $ 13,760 $ — $ (1,747 ) $ 12,013 $ 22,291 $ — $ (4,079 ) $ 18,212 Trading Securities $ 20,447 $ 17,920
Trading Securities	A summary of the Company's securities portfolio by category and maturity is presented in the following tables. Securities Portfolio (Dollar amounts in thousands) As of December 31, 2017 2016 Amortized Cost Gross Unrealized Fair Value Amortized Cost Gross Unrealized Fair Gains Losses Gains Losses Securities Available-for-Sale U.S. treasury securities $ 46,529 $ — $ (184 ) $ 46,345 $ 48,581 $ 26 $ (66 ) $ 48,541 U.S. agency securities 157,636 197 (986 ) 156,847 183,528 519 (410 ) 183,637 Collateralized mortgage 1,113,019 121 (17,954 ) 1,095,186 1,064,130 969 (17,653 ) 1,047,446 Other mortgage-backed 373,676 201 (4,334 ) 369,543 337,139 1,395 (5,879 ) 332,655 Municipal securities 209,558 693 (1,260 ) 208,991 273,319 1,245 (3,718 ) 270,846 Trust-preferred collateralized debt obligations ("CDOs") — — — — 47,681 261 (14,682 ) 33,260 Equity securities 7,408 194 (305 ) 7,297 3,206 147 (288 ) 3,065 Total securities available-for-sale $ 1,907,826 $ 1,406 $ (25,023 ) $ 1,884,209 $ 1,957,584 $ 4,562 $ (42,696 ) $ 1,919,450 Securities Held-to-Maturity Municipal securities $ 13,760 $ — $ (1,747 ) $ 12,013 $ 22,291 $ — $ (4,079 ) $ 18,212 Trading Securities $ 20,447 $ 17,920
Remaining Contractual Maturity of Securities	Remaining Contractual Maturity of Securities (Dollar amounts in thousands) As of December 31, 2017 Available-for-Sale Held-to-Maturity Amortized Cost Fair Value Amortized Cost Fair Value One year or less $ 87,379 $ 87,053 $ 1,432 $ 1,250 After one year to five years 323,203 322,000 5,831 5,090 After five years to ten years 3,141 3,130 2,243 1,959 After ten years — — 4,254 3,714 Securities that do not have a single contractual maturity date 1,494,103 1,472,026 — — Total $ 1,907,826 $ 1,884,209 $ 13,760 $ 12,013
Securities Available-for-Sale (Losses) Gains	The following table presents net realized (losses) gains on securities available-for-sale for the three years ended December 31, 2017 . Securities Available-for-Sale (Losses) Gains (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Gains (losses) on sales of securities: Gross realized gains $ 5,478 $ 1,589 $ 2,519 Gross realized losses (7,354 ) (169 ) (146 ) Net realized (losses) gains on sales of securities (1,876 ) 1,420 2,373 Non-cash impairment charges: OTTI — — — Net realized (losses) gains $ (1,876 ) $ 1,420 $ 2,373
Changes in OTTI Recognized in Earnings	The following table presents a rollforward of life-to-date OTTI recognized in earnings related to all securities available-for-sale held by the Company for the years ended December 31, 2017 , 2016 , and 2015 . Changes in OTTI Recognized in Earnings (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 23,345 $ 23,345 $ 23,516 OTTI included in earnings (1) : Losses on securities that previously had OTTI — — — Losses on securities that did not previously have OTTI — — — Reduction for securities sales (2) (23,345 ) — (171 ) Ending balance $ — $ 23,345 $ 23,345 (1) Included in net securities (losses) gains in the Consolidated Statements of Income. (2) These reductions were driven by the sale of 11 CDOs with a carrying value of $47.7 million during the year ended December 31, 2017 and one CMO with a carrying value of $1.3 million during the year ended December 31, 201
Securities in an Unrealized Loss Position	The following table presents the aggregate amount of unrealized losses and the aggregate related fair values of securities with unrealized losses as of December 31, 2017 and 2016 . Securities in an Unrealized Loss Position (Dollar amounts in thousands) Less Than 12 Months Greater Than 12 Months Total Number of Securities Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses As of December 31, 2017 Securities Available-for-Sale U.S. treasury securities 20 $ 19,918 $ 87 $ 26,427 $ 97 $ 46,345 $ 184 U.S. agency securities 72 66,899 300 58,021 686 124,920 986 CMOs 211 365,131 3,265 633,227 14,689 998,358 17,954 MBSs 86 126,136 902 210,017 3,432 336,153 4,334 Municipal securities 265 35,500 479 81,360 781 116,860 1,260 Equity securities 2 391 214 6,386 91 6,777 305 Total 656 $ 613,975 $ 5,247 $ 1,015,438 $ 19,776 $ 1,629,413 $ 25,023 Securities Held-to-Maturity Municipal securities 8 $ — $ — $ 12,013 $ 1,747 $ 12,013 $ 1,747 As of December 31, 2016 Securities Available-for-Sale U.S. treasury securities 16 $ 33,505 $ 61 $ 3,995 $ 5 $ 37,500 $ 66 U.S. agency securities 28 62,064 364 11,814 46 73,878 410 CMOs 194 523,233 10,309 411,758 7,344 934,991 17,653 MBSs 68 221,174 4,726 77,780 1,154 298,954 5,880 Municipal securities 380 133,957 3,059 29,280 659 163,237 3,718 CDOs 7 — — 30,592 14,682 30,592 14,682 Equity securities 2 404 201 2,319 86 2,723 287 Total 695 $ 974,337 $ 18,720 $ 567,538 $ 23,976 $ 1,541,875 $ 42,696 Securities Held-to-Maturity Municipal securities 14 $ — $ — $ 18,212 $ 4,079 $ 18,212 $ 4,079

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Composition Of Loan Portfolio	The following table presents the Company's loans held-for-investment by class. Loan Portfolio (Dollar amounts in thousands) As of December 31, 2017 2016 Commercial and industrial $ 3,529,914 $ 2,827,658 Agricultural 430,886 389,496 Commercial real estate: Office, retail, and industrial 1,979,820 1,581,967 Multi-family 675,463 614,052 Construction 539,820 451,540 Other commercial real estate 1,358,515 979,528 Total commercial real estate 4,553,618 3,627,087 Total corporate loans 8,514,418 6,844,241 Home equity 827,055 747,983 1-4 family mortgages 774,357 423,922 Installment 321,982 237,999 Total consumer loans 1,923,394 1,409,904 Total loans $ 10,437,812 $ 8,254,145 Deferred loan fees included in total loans $ 4,986 $ 3,838 Overdrawn demand deposits included in total loans 8,587 7,836
Schedule of Financial Instruments Owned and Pledged as Collateral	The carrying value of loans that were pledged to secure liabilities as of December 31, 2017 and 2016 are presented below. Carrying Value of Loans Pledged (Dollar amounts in thousands) As of December 31 2017 2016 Loans pledged to secure: FHLB advances (blanket pledge) $ 4,587,240 $ 3,667,202 FRB's Discount Window Primary Credit Program 1,099,712 777,950 Total $ 5,686,952 $ 4,445,152
Schedule of Loans Sold	The following table presents loan sales for the years ended December 31, 2017 , 2016 , and 2015 . Loan Sales (Dollar amounts in thousands) As of December 31, 2017 2016 2015 Corporate loan sales Proceeds from sales $ 52,974 $ 54,681 $ 31,091 Less book value of loans sold 51,781 52,821 29,535 Net gains on corporate sales (1) $ 1,193 $ 1,860 $ 1,556 1-4 family mortgage loan sales Proceeds from sales $ 258,626 $ 290,383 $ 185,308 Less book value of loans sold 252,741 283,312 180,017 Net gains on 1-4 family mortgage sales (2) 5,885 7,071 5,291 Total net gains on loan sales $ 7,078 $ 8,931 $ 6,847 (1) Net gains on corporate loan sales are included in other service charges, commissions, and fees in the Consolidated Statements of Income. (2) Net gains on mortgage loan sales are included in mortgage banking income in the Consolidated Statements of Income.

Acquired and Covered Loans (Tab

Acquired and Covered Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Acquired Loans [Abstract]
Acquired and Covered Loans	The following table presents acquired and covered PCI and Non-PCI loans as of December 31, 2017 and 2016 . Acquired and Covered Loans (Dollar amounts in thousands) As of December 31, 2017 2016 PCI Non-PCI Total PCI Non-PCI Total Acquired loans $ 130,694 $ 1,512,664 $ 1,643,358 $ 53,772 $ 613,339 $ 667,111 Covered loans 6,759 11,789 18,548 7,895 15,379 23,274 Total acquired and covered loans $ 137,453 $ 1,524,453 $ 1,661,906 $ 61,667 $ 628,718 $ 690,385
Changes In The FDIC Indemnification Asset	A rollforward of the carrying value of the FDIC indemnification asset for the three years ended December 31, 2017 is presented in the following table. Changes in the FDIC Indemnification Asset (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 4,522 $ 3,903 $ 8,452 Amortization (1,208 ) (1,185 ) (1,461 ) Change in expected reimbursements from the FDIC for changes in expected credit losses (792 ) 330 1,313 Net payments to (from) the FDIC 792 1,474 (4,401 ) Ending balance $ 3,314 $ 4,522 $ 3,903
Changes In Accretable Yield For Purchased Credit Impaired Loans	Changes in the accretable yield for acquired and covered PCI loans were as follows. Changes in Accretable Yield (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 19,386 $ 24,912 $ 28,244 Additions 27,316 3,981 1,168 Accretion (15,529 ) (8,063 ) (11,311 ) Other (1) 1,784 (1,444 ) 6,811 Ending balance $ 32,957 $ 19,386 $ 24,912 (1) Increases represent a rise in the expected future cash flows to be collected over the remaining estimated life of the underlying portfolio while decreases result from the resolution of certain loans occurring earlier than anticipated.

Past Due Loans, Allowance For38

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs (Tables)	12 Months Ended
	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Past Due Financing Receivables	The following table presents an aging analysis of the Company's past due loans as of December 31, 2017 and 2016 . The aging is determined without regard to accrual status. The table also presents non-performing loans, consisting of non-accrual loans (the majority of which are past due) and loans 90 days or more past due and still accruing interest, as of each balance sheet date. Aging Analysis of Past Due Loans and Non-Performing Loans by Class (Dollar amounts in thousands) Aging Analysis (Accruing and Non-accrual) Non-performing Loans Current (1) 30-89 Days Past Due 90 Days or More Past Due Total Past Due Total Loans Non-accrual (2) 90 Days or More Past Due, Still Accruing Interest As of December 31, 2017 Commercial and industrial $ 3,490,783 $ 34,620 $ 4,511 $ 39,131 $ 3,529,914 $ 40,580 $ 1,830 Agricultural 430,221 280 385 665 430,886 219 177 Commercial real estate: Office, retail, and industrial 1,970,564 3,156 6,100 9,256 1,979,820 11,560 345 Multi-family 672,098 3,117 248 3,365 675,463 377 20 Construction 539,043 198 579 777 539,820 209 371 Other commercial real estate 1,353,263 2,545 2,707 5,252 1,358,515 3,621 317 Total commercial real estate 4,534,968 9,016 9,634 18,650 4,553,618 15,767 1,053 Total corporate loans 8,455,972 43,916 14,530 58,446 8,514,418 56,566 3,060 Home equity 820,099 4,102 2,854 6,956 827,055 5,946 98 1-4 family mortgages 770,120 2,145 2,092 4,237 774,357 4,412 — Installment 319,178 2,407 397 2,804 321,982 — 397 Total consumer loans 1,909,397 8,654 5,343 13,997 1,923,394 10,358 495 Total loans $ 10,365,369 $ 52,570 $ 19,873 $ 72,443 $ 10,437,812 $ 66,924 $ 3,555 As of December 31, 2016 Commercial and industrial $ 2,816,442 $ 6,426 $ 4,790 $ 11,216 $ 2,827,658 $ 29,938 $ 374 Agricultural 388,596 — 900 900 389,496 181 736 Commercial real estate: Office, retail, and industrial 1,564,007 5,327 12,633 17,960 1,581,967 17,277 1,129 Multi-family 612,446 858 748 1,606 614,052 311 604 Construction 450,927 332 281 613 451,540 286 — Other commercial real estate 974,575 1,307 3,646 4,953 979,528 2,892 1,526 Total commercial real estate 3,601,955 7,824 17,308 25,132 3,627,087 20,766 3,259 Total corporate loans 6,806,993 14,250 22,998 37,248 6,844,241 50,885 4,369 Home equity 740,919 4,545 2,519 7,064 747,983 5,465 109 1-4 family mortgages 420,264 2,652 1,006 3,658 423,922 2,939 272 Installment 236,264 1,476 259 1,735 237,999 — 259 Total consumer loans 1,397,447 8,673 3,784 12,457 1,409,904 8,404 640 Total loans $ 8,204,440 $ 22,923 $ 26,782 $ 49,705 $ 8,254,145 $ 59,289 $ 5,009 (1) PCI loans with an accretable yield are considered current. (2) Includes PCI loans of $763,000 and $681,000 as of December 31, 2017 and December 31, 2016 , respectively, which no longer have an accretable yield as estimates of expected future cash flows have decreased since the acquisition due to credit deterioration.
Allowance For Credit Losses On Financing Receivables	A rollforward of the allowance for credit losses by portfolio segment for the years ended December 31, 2017 , 2016 , and 2015 is presented in the table below. Allowance for Credit Losses by Portfolio Segment (Dollar amounts in thousands) Commercial, Industrial, and Agricultural Office, Retail, and Industrial Multi-family Construction Other Commercial Real Estate Consumer Reserve for Unfunded Commitments Total Allowance for Credit Losses Year Ended December 31, 2017 Beginning balance $ 40,709 $ 17,595 $ 3,261 $ 3,444 $ 7,739 $ 13,335 $ 1,000 $ 87,083 Charge-offs (22,885 ) (190 ) — (38 ) (755 ) (6,955 ) — (30,823 ) Recoveries 4,150 2,935 39 270 244 1,541 — 9,179 Net charge-offs (18,735 ) 2,745 39 232 (511 ) (5,414 ) — (21,644 ) Provision for loan 33,817 (9,344 ) (766 ) (195 ) (847 ) 8,625 — 31,290 Ending Balance $ 55,791 $ 10,996 $ 2,534 $ 3,481 $ 6,381 $ 16,546 $ 1,000 $ 96,729 Year Ended December 31, 2016 Beginning balance $ 37,074 $ 13,124 $ 2,469 $ 1,440 $ 6,109 $ 13,414 $ 1,225 $ 74,855 Charge-offs (9,982 ) (4,707 ) (307 ) (134 ) (2,932 ) (5,231 ) — (23,293 ) Recoveries 2,451 337 97 56 524 1,298 — 4,763 Net charge-offs (7,531 ) (4,370 ) (210 ) (78 ) (2,408 ) (3,933 ) — (18,530 ) Provision for loan losses and other 11,166 8,841 1,002 2,082 4,038 3,854 (225 ) 30,758 Ending balance $ 40,709 $ 17,595 $ 3,261 $ 3,444 $ 7,739 $ 13,335 $ 1,000 $ 87,083 Year Ended December 31, 2015 Beginning balance $ 31,177 $ 13,053 $ 2,387 $ 3,031 $ 9,019 $ 14,027 $ 1,816 $ 74,510 Charge-offs (16,422 ) (2,899 ) (568 ) (139 ) (2,678 ) (4,211 ) — (26,917 ) Recoveries 2,588 534 15 350 2,031 1,183 — 6,701 Net charge-offs (13,834 ) (2,365 ) (553 ) 211 (647 ) (3,028 ) — (20,216 ) Provision for loan 19,731 2,436 635 (1,802 ) (2,263 ) 2,415 (591 ) 20,561 Ending balance $ 37,074 $ 13,124 $ 2,469 $ 1,440 $ 6,109 $ 13,414 $ 1,225 $ 74,855
Schedule of Loans and The Related Allowance for Credit Losses	The table below provides a breakdown of loans and the related allowance for credit losses by portfolio segment as of December 31, 2017 and 2016 . Loans and Related Allowance for Credit Losses by Portfolio Segment (Dollar amounts in thousands) Loans Allowance for Credit Losses Individually Evaluated for Impairment Collectively Evaluated for Impairment PCI Total Individually Evaluated for Impairment Collectively Evaluated for Impairment PCI Total As of December 31, 2017 Commercial, industrial, and $ 38,718 $ 3,909,380 $ 12,702 $ 3,960,800 $ 10,074 $ 45,293 $ 424 $ 55,791 Commercial real estate: Office, retail, and industrial 10,810 1,954,435 14,575 1,979,820 — 9,333 1,663 10,996 Multi-family 621 660,771 14,071 675,463 — 2,436 98 2,534 Construction — 530,977 8,843 539,820 — 3,331 150 3,481 Other commercial real estate 1,468 1,291,723 65,324 1,358,515 — 5,415 966 6,381 Total commercial real estate 12,899 4,437,906 102,813 4,553,618 — 20,515 2,877 23,392 Total corporate loans 51,617 8,347,286 115,515 8,514,418 10,074 65,808 3,301 79,183 Consumer — 1,901,456 21,938 1,923,394 — 15,533 1,013 16,546 Reserve for unfunded — — — — — 1,000 — 1,000 Total loans $ 51,617 $ 10,248,742 $ 137,453 $ 10,437,812 $ 10,074 $ 82,341 $ 4,314 $ 96,729 As of December 31, 2016 Commercial, industrial, and $ 24,645 $ 3,189,327 $ 3,182 $ 3,217,154 $ 507 $ 39,554 $ 648 $ 40,709 Commercial real estate: Office, retail, and industrial 16,287 1,553,234 12,446 1,581,967 — 16,148 1,447 17,595 Multi-family 398 601,429 12,225 614,052 — 3,059 202 3,261 Construction 34 447,058 4,448 451,540 — 3,280 164 3,444 Other commercial real estate 1,286 965,900 12,342 979,528 18 6,613 1,108 7,739 Total commercial real estate 18,005 3,567,621 41,461 3,627,087 18 29,100 2,921 32,039 Total corporate loans 42,650 6,756,948 44,643 6,844,241 525 68,654 3,569 72,748 Consumer — 1,392,880 17,024 1,409,904 — 12,210 1,125 13,335 Reserve for unfunded — — — — — 1,000 — 1,000 Total loans $ 42,650 $ 8,149,828 $ 61,667 $ 8,254,145 $ 525 $ 81,864 $ 4,694 $ 87,083
Impaired Financing Receivables	The following table presents loans individually evaluated for impairment by class of loan as of December 31, 2017 and 2016 . PCI loans are excluded from this disclosure. Impaired Loans Individually Evaluated by Class (Dollar amounts in thousands) As of December 31, 2017 2016 Recorded Investment In Recorded Investment In Loans with No Specific Reserve Loans with a Specific Reserve Unpaid Principal Balance Specific Reserve Loans with No Specific Reserve Loans with a Specific Reserve Unpaid Principal Balance Specific Reserve Commercial and industrial $ 4,234 $ 34,484 $ 53,192 $ 10,074 $ 11,579 $ 13,066 $ 29,514 $ 507 Agricultural — — — — — — — — Commercial real estate: Office, retail, and industrial 7,154 3,656 14,246 — 16,287 — 21,057 — Multi-family 621 — 621 — 398 — 398 — Construction — — — — 34 — 34 — Other commercial real estate 1,468 — 1,566 — 1,016 270 2,141 18 Total commercial real estate 9,243 3,656 16,433 — 17,735 270 23,630 18 Total impaired loans $ 13,477 $ 38,140 $ 69,625 $ 10,074 $ 29,314 $ 13,336 $ 53,144 $ 525 The following table presents the average recorded investment and interest income recognized on impaired loans by class for the years ended December 31, 2017 , 2016 , and 2015 . PCI loans are excluded from this disclosure. Average Recorded Investment and Interest Income Recognized on Impaired Loans by Class (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Average Recorded Investment Interest Income Recognized (1) Average Recorded Investment Interest Income Recognized (1) Average Interest (1) Commercial and industrial $ 33,956 $ 1,059 $ 9,178 $ 104 $ 8,940 $ 163 Agricultural 279 101 — — — — Commercial real estate: Office, retail, and industrial 13,106 325 12,867 291 9,359 52 Multi-family 441 28 479 11 855 13 Construction 7 136 63 — 3,902 118 Other commercial real estate 1,615 41 2,809 86 3,310 44 Total commercial real estate 15,170 530 16,218 388 17,426 227 Total impaired loans $ 49,404 $ 1,690 $ 25,396 $ 492 $ 26,366 $ 390 (1) Recorded using the cash basis of accounting.
Financing Receivable Credit Quality Indicators	Consumer Credit Quality Indicators by Class (Dollar amounts in thousands) Performing Non-accrual Total As of December 31, 2017 Home equity $ 821,109 $ 5,946 $ 827,055 1-4 family mortgages 769,945 4,412 774,357 Installment 321,982 — 321,982 Total consumer loans $ 1,913,036 $ 10,358 $ 1,923,394 As of December 31, 2016 Home equity $ 742,518 $ 5,465 $ 747,983 1-4 family mortgages 420,983 2,939 423,922 Installment 237,999 — 237,999 Total consumer loans $ 1,401,500 $ 8,404 $ 1,409,904 The following tables present credit quality indicators by class for corporate and consumer loans as of December 31, 2017 and 2016 . Corporate Credit Quality Indicators by Class (Dollar amounts in thousands) Pass Special (1)(4) Substandard (2)(4) Non-accrual (3) Total As of December 31, 2017 Commercial and industrial $ 3,388,133 $ 70,863 $ 30,338 $ 40,580 $ 3,529,914 Agricultural 413,946 10,989 5,732 219 430,886 Commercial real estate: Office, retail, and industrial 1,903,737 25,546 38,977 11,560 1,979,820 Multi-family 665,496 7,395 2,195 377 675,463 Construction 521,911 10,184 7,516 209 539,820 Other commercial real estate 1,304,337 29,624 20,933 3,621 1,358,515 Total commercial real estate 4,395,481 72,749 69,621 15,767 4,553,618 Total corporate loans $ 8,197,560 $ 154,601 $ 105,691 $ 56,566 $ 8,514,418 As of December 31, 2016 Commercial and industrial $ 2,638,833 $ 92,340 $ 66,547 $ 29,938 $ 2,827,658 Agricultural 366,382 17,039 5,894 181 389,496 Commercial real estate: Office, retail, and industrial 1,491,170 34,007 39,513 17,277 1,581,967 Multi-family 607,342 4,370 2,029 311 614,052 Construction 438,946 111 12,197 286 451,540 Other commercial real estate 951,284 11,808 13,544 2,892 979,528 Total commercial real estate 3,488,742 50,296 67,283 20,766 3,627,087 Total corporate loans $ 6,493,957 $ 159,675 $ 139,724 $ 50,885 $ 6,844,241 (1) Loans categorized as special mention exhibit potential weaknesses that require the close attention of management since these potential weaknesses may result in the deterioration of repayment prospects in the future. (2) Loans categorized as substandard exhibit a well-defined weakness that may jeopardize the liquidation of the debt. These loans continue to accrue interest because they are well-secured and collection of principal and interest is expected within a reasonable time. (3) Loans categorized as non-accrual exhibit a well-defined weakness that may jeopardize the liquidation of the debt or result in a loss if the deficiencies are not corrected. (4) Total special mention and substandard loans includes accruing TDRs of $657,000 as of December 31, 2017 and $834,000 as of December 31, 2016 .
Troubled Debt Restructurings on Financing Receivables	A rollforward of the carrying value of TDRs for the years ended December 31, 2017 , 2016 , and 2015 is presented in the following table. TDR Rollforward (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Accruing Beginning balance $ 2,291 $ 2,743 $ 3,704 Additions 15,819 — 120 Net payments (1,923 ) (120 ) (774 ) Returned to performing status — — — Net transfers to non-accrual (14,391 ) (332 ) (307 ) Ending balance 1,796 2,291 2,743 Non-accrual Beginning balance 6,297 2,324 19,904 Additions 14,570 6,205 325 Net payments (4,380 ) (1,072 ) (15,525 ) Charge-offs (6,345 ) (1,492 ) (2,687 ) Transfers to OREO — — — Loans sold — — — Net transfers from accruing 14,391 332 307 Ending balance 24,533 6,297 2,324 Total TDRs $ 26,329 $ 8,588 $ 5,067 The table below presents TDRs by class as of December 31, 2017 and 2016 . See Note 1 , " Summary of Significant Accounting Policies ," for the accounting policy for TDRs. TDRs by Class (Dollar amounts in thousands) As of December 31, 2017 2016 Accruing Non-accrual (1) Total Accruing Non-accrual (1) Total Commercial and industrial $ 264 $ 18,959 $ 19,223 $ 281 $ 150 $ 431 Agricultural — — — — — — Commercial real estate: Office, retail, and industrial — 4,236 4,236 155 4,733 4,888 Multi-family 574 149 723 586 168 754 Construction — — — — — — Other commercial real estate 192 — 192 268 48 316 Total commercial real estate 766 4,385 5,151 1,009 4,949 5,958 Total corporate loans 1,030 23,344 24,374 1,290 5,099 6,389 Home equity 86 738 824 177 820 997 1-4 family mortgages 680 451 1,131 824 378 1,202 Installment — — — — — — Total consumer loans 766 1,189 1,955 1,001 1,198 2,199 Total loans $ 1,796 $ 24,533 $ 26,329 $ 2,291 $ 6,297 $ 8,588 (1) These TDRs are included in non-accrual loans in the preceding tables. The following table presents a summary of loans that were restructured during the years ended December 31, 2017 , 2016 , and 2015 . Loans Restructured During the Period (Dollar amounts in thousands) Number of Loans Pre-Modification Recorded Investment Funds Disbursed Interest and Escrow Capitalized Charge-offs Post-Modification Recorded Investment Year Ended December 31, 2017 Commercial and industrial 12 $ 26,733 $ 9,035 $ — $ 6,232 $ 29,536 Office, retail, and industrial 2 3,656 — — — 3,656 Total loans restructured during the period 14 $ 30,389 $ 9,035 $ — $ 6,232 $ 33,192 Year Ended December 31, 2016 Office, retail, and industrial 1 $ 5,460 $ — $ — $ 1,083 $ 4,377 Other commercial real estate 1 745 — — — 745 Total loans restructured during the period 2 $ 6,205 $ — $ — $ 1,083 $ 5,122 Year Ended December 31, 2015 Home equity 1 $ 120 $ — $ — $ — $ 120 1-4 family mortgages 2 325 — — — 325 Total loans restructured during the period 3 $ 445 $ — $ — $ — $ 445 The following table presents TDRs that had payment defaults during the years ended December 31, 2017 , 2016 , and 2015 where the default occurred within twelve months of the restructure date. TDRs That Defaulted Within Twelve Months of the Restructured Date (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment Home equity — $ — 1 $ 119 — $ — Total — $ — 1 $ 119 — $ —

Premises, Furniture, and Equi39

Premises, Furniture, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table summarizes the Company's premises, furniture, and equipment by category. Premises, Furniture, and Equipment (Dollar amounts in thousands) As of December 31, 2017 2016 Land $ 30,470 $ 18,304 Premises 123,873 94,369 Furniture and equipment 115,013 105,859 Total cost 269,356 218,532 Accumulated depreciation (148,248 ) (140,030 ) Net book value of premises, furniture, and equipment 121,108 78,502 Assets held-for-sale 2,208 4,075 Premises, furniture, and equipment, net $ 123,316 $ 82,577
Schedule of Future Minimum Lease Payments for Capital Leases	The following summary reflects the future minimum payments by year required under operating leases that have initial or remaining non-cancelable lease terms in excess of one year as of December 31, 2017 . Future Minimum Operating Lease Payments (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 19,241 2019 17,659 2020 16,926 2021 16,732 2022 16,464 2023 and thereafter 119,847 Total minimum lease payments $ 206,869
Scheduled Accretion of Operating Leases	The following table presents the remaining scheduled accretion of the intangible liability by year. Scheduled Accretion of Operating Lease Intangible (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 935 2019 685 2020 648 2021 648 2022 639 2023 and thereafter 3,358 Total accretion $ 6,913
Schedule Of Rental Expense And Income	The following table presents net operating lease expense for the years ended December 31, 2017 , 2016 , and 2015 . Net Operating Lease Expense (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Lease expense charged to operations $ 18,666 $ 11,207 $ 6,850 Accretion of operating lease intangible (1) (1,180 ) (1,171 ) (1,144 ) Accretion of deferred gain on sale-leaseback transaction (1) (5,872 ) (1,473 ) — Rental income from premises leased to others (1) (682 ) (527 ) (606 ) Net operating lease expense $ 10,932 $ 8,036 $ 5,100 (1) Included as reductions to net occupancy and equipment expense in the Consolidated Statements of Income.

Goodwill and Other Intangible40

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The following table presents changes in the carrying amount of goodwill for the years ended December 31, 2017 , 2016 , and 2015 . Changes in the Carrying Amount of Goodwill (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 340,879 $ 319,007 $ 310,589 Acquisitions 356,729 21,872 8,418 Ending balance $ 697,608 $ 340,879 $ 319,007
Schedule of Finite-Lived Intangible Assets	Other Intangible Assets (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Gross Accumulated Amortization Net Beginning balance $ 58,959 $ 32,962 $ 25,997 $ 48,550 $ 28,280 $ 20,270 $ 47,970 $ 24,360 $ 23,610 Additions 39,017 — 39,017 10,409 — 10,409 580 — 580 Amortization expense — 7,865 (7,865 ) — 4,682 (4,682 ) — 3,920 (3,920 ) Ending balance $ 97,976 $ 40,827 $ 57,149 $ 58,959 $ 32,962 $ 25,997 $ 48,550 $ 28,280 $ 20,270 Weighted-average remaining life (in years) 8.3 7.6 7.4 Estimated remaining useful lives (in years) 0.2 to 9.3 0.6 to 9.3 0.8 to 10.0
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Scheduled Amortization of Other Intangible Assets (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 7,139 2019 7,073 2020 7,023 2021 6,946 2022 6,867 2023 and thereafter 22,101 Total $ 57,149

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Schedule of Deposits	The following table presents the Company's deposits by type. Summary of Deposits (Dollar amounts in thousands) As of December 31, 2017 2016 Demand deposits $ 3,576,190 $ 2,766,748 Savings deposits 2,011,999 1,615,833 NOW accounts 1,962,304 1,675,421 Money market deposits 1,856,049 1,577,316 Time deposits less than $100,000 904,882 755,558 Time deposits greater than $100,000 741,901 437,727 Total deposits $ 11,053,325 $ 8,828,603
Schedule of Maturities of Time Deposits	The following table provides maturity information related to the Company's time deposits. Scheduled Maturities of Time Deposits (Dollar amounts in thousands) Total Year Ending December 31, 2018 $ 1,086,528 2019 418,176 2020 86,196 2021 38,569 2022 16,845 2023 and thereafter 469 Total $ 1,646,783

Borrowed Funds (Tables)

Borrowed Funds (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Debt	The following table summarizes the Company's borrowed funds by funding source. Summary of Borrowed Funds (Dollar amounts in thousands) As of December 31, 2017 2016 Securities sold under agreements to repurchase $ 124,884 $ 129,008 FHLB advances 590,000 750,000 Total borrowed funds $ 714,884 $ 879,008
Unused Short-Term Credit Lines Available for Use	The following table presents short-term credit lines available for use, for which the Company did not have an outstanding balance as of December 31, 2017 and 2016 . Short-Term Credit Lines Available for Use (Dollar amounts in thousands) As of December 31, 2017 2016 FRBs Discount Window Primary Credit Program $ 843,618 $ 629,699 Available federal funds lines 667,000 632,000 Correspondent bank line of credit 50,000 50,000

Senior and Subordinated Debt (T

Senior and Subordinated Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	The following table presents the Company's senior and subordinated debt by issuance. Senior and Subordinated Debt (Dollar amounts in thousands) As of December 31, Issuance Date Maturity Date Interest Rate 2017 2016 Subordinated notes September 2016 September 2026 5.875% $ 146,927 $ 146,573 Junior subordinated debentures: First Midwest Capital Trust I ("FMCT") November 2003 December 2033 6.950% 37,801 37,800 Great Lakes Statutory Trust II ("GLST II") (1) December 2005 December 2035 L+1.400% (2) 4,486 4,391 Great Lakes Statutory Trust III ("GLST III") (1) June 2007 September 2037 L+1.700% (2) 5,956 5,839 Total junior subordinated debentures 48,243 48,030 Total senior and subordinated debt $ 195,170 $ 194,603 (1) The junior subordinated debentures related to GLST II and GLST III were assumed by the Company through an acquisition. As of December 31, 2017, these amounts include acquisition adjustments which resulted in a discount of $1.7 million to GLST II and $2.3 million to GLST III. The acquisition adjustments totaled $1.8 million and $2.4 million to GLST II and GLST III, respectively, as of December 31, 2016. (2) The interest rates are a variable rate based on the three-month LIBOR plus 1.400% and 1.700% for GLST II and GLST III, respectively.

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The table below displays the calculation of basic and diluted EPS. Basic and Diluted EPS (Amounts in thousands, except per share data) Years Ended December 31, 2017 2016 2015 Net income $ 98,387 $ 92,349 $ 82,064 Net income applicable to non-vested restricted shares (916 ) (1,043 ) (882 ) Net income applicable to common shares $ 97,471 $ 91,306 $ 81,182 Weighted-average common shares outstanding: Weighted-average common shares outstanding (basic) 101,423 79,797 77,059 Dilutive effect of common stock equivalents 20 13 13 Weighted-average diluted common shares outstanding 101,443 79,810 77,072 Basic EPS $ 0.96 $ 1.14 $ 1.05 Diluted EPS 0.96 1.14 1.05 Anti-dilutive shares not included in the computation of diluted EPS (1) 229 494 800 (1) This amount represents outstanding stock options for which the exercise price is greater than the average market price of the Company's common stock.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Components of Income Tax Expense (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Current income tax expense: Federal $ 93,540 $ 46,748 $ 18,524 State 104 790 2,326 Total 93,644 47,538 20,850 Deferred income tax (benefit) expense: Federal (12,219 ) (7,786 ) 12,048 State 8,142 6,419 4,849 Total (4,077 ) (1,367 ) 16,897 Total income tax expense $ 89,567 $ 46,171 $ 37,747
Schedule of Effective Income Tax Rate Reconciliation	Components of Effective Tax Rate (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Amount % of Pretax Income Amount % of Pretax Income Amount % of Pretax Income Statutory federal income tax $ 65,784 35.0 % $ 48,482 35.0 % $ 41,934 35.0 % Increase (decrease) in income taxes resulting from: Revaluation of deferred tax assets 23,709 12.6 — — — — Tax-exempt income, net of interest expense disallowance (5,065 ) (2.7 ) (5,439 ) (3.9 ) (6,752 ) (5.6 ) State income tax, net of federal income tax effect 5,069 2.7 4,323 3.1 4,665 3.9 Other 70 0.1 (1,195 ) (0.9 ) (2,100 ) (1.8 ) Total $ 89,567 47.7 % $ 46,171 33.3 % $ 37,747 31.5 %
Schedule of Deferred Tax Assets and Liabilities	Deferred Tax Assets and Liabilities (Dollar amounts in thousands) As of December 31, 2017 2016 Deferred tax assets: Allowance for credit losses $ 20,285 $ 30,399 Deferred gain on sale-leaseback transaction 15,668 28,133 Equity based compensation 3,605 5,228 Federal and state net operating loss ("NOL") carryforwards 3,384 388 Acquisition adjustments 2,489 — OREO 2,089 4,336 Non-equity based compensation 897 6,060 AMT and other credit carryforwards 667 90 Unrealized losses on securities 23 18,320 Other 12,494 10,997 Total deferred tax assets 61,601 103,951 Deferred tax liabilities: Deferred loan fees and costs (4,169 ) (3,172 ) Accrued retirement benefits (3,517 ) (6,281 ) Fixed assets (1,660 ) (397 ) Cancellation of indebtedness income (641 ) (2,136 ) Acquisition adjustments — (13,407 ) Other (2,449 ) (6,045 ) Total deferred tax liabilities (12,436 ) (31,438 ) Deferred tax valuation allowance — — Net deferred tax assets 49,165 72,513 Tax effect of adjustments related to other comprehensive income (loss) 15,571 27,694 Net deferred tax assets including adjustments $ 64,736 $ 100,207 NOL carryforwards available to offset future taxable income: Federal gross NOL carryforwards, begin to expire in 2035 $ — $ 574 Illinois gross NOL carryforwards, begin to expire in 2025 188,995 26,342 Indiana gross NOL carryforwards, begin to expire in 2025 16,174 1,003 AMT credits 410 —
Summary of Income Tax Contingencies	Rollforward of Unrecognized Tax Benefits (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 2,039 $ 1,408 $ 912 Additions for tax positions relating to the current year 845 640 480 Additions for tax positions relating to prior years 13,389 — 37 Reductions for tax positions relating to prior years (25 ) (9 ) (21 ) Ending balance $ 16,248 $ 2,039 $ 1,408 Interest and penalties not included above (1) : Interest expense, net of tax effect, and penalties $ 118 $ 49 $ 20 Accrued interest and penalties, net of tax effect, at end of year 191 73 24 (1) Included in income tax expense in the Consolidated Statements of Income.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Profit Sharing Plan	Profit Sharing Plan (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Profit sharing expense (1) $ 7,346 $ 6,171 $ 6,919 Company dividends received by the Profit Sharing Plan $ 441 $ 494 $ 466 Company shares held by the Profit Sharing Plan at the end of the year: Number of shares 1,079,975 1,175,858 1,277,567 Fair value $ 25,930 $ 29,667 $ 23,546 (1) Included in retirement and other employee benefits in the Consolidated Statements of Income.
Schedule of Pension Plan Cost and Obligation	Pension Plan Cost and Obligations (Dollar amounts in thousands) As of December 31, 2017 2016 Accumulated benefit obligation $ 67,923 $ 68,959 Change in projected benefit obligation Beginning balance $ 68,959 $ 67,185 Service cost — — Interest cost 1,712 1,635 Settlements (6,271 ) (3,136 ) Actuarial loss 4,240 3,851 Benefits paid (717 ) (576 ) Ending balance $ 67,923 $ 68,959 Change in fair value of plan assets Beginning balance $ 65,189 $ 64,903 Actual return on plan assets 7,958 3,998 Benefits paid (717 ) (576 ) Settlements (6,271 ) (3,136 ) Ending balance $ 66,159 $ 65,189 Funded status recognized in the Consolidated Statements of Financial Condition Noncurrent liability $ (1,764 ) $ (3,770 ) Amounts recognized in accumulated other comprehensive loss Prior service cost $ — $ — Net loss 25,495 28,483 Net amount recognized $ 25,495 $ 28,483 Actuarial losses included in accumulated other comprehensive loss as a percent of Accumulated benefit obligation 37.5 % 41.3 % Fair value of plan assets 38.5 % 43.7 % Amounts expected to be amortized from accumulated other comprehensive loss into net periodic benefit cost in the next fiscal year Prior service cost $ — $ — Net loss 561 582 Net amount expected to be recognized $ 561 $ 582 Weighted-average assumptions at the end of the year used to determine the actuarial present value of the projected benefit obligation Discount rate 3.45 % 3.86 %
Schedule of Net Periodic Benefit Pension Costs	Net Periodic Benefit Pension Cost (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Components of net periodic benefit cost Interest cost $ 1,712 $ 1,635 $ 2,334 Expected return on plan assets (3,802 ) (4,057 ) (4,333 ) Recognized net actuarial loss 591 571 367 Amortization of prior service cost — — — Recognized settlement loss 2,480 1,338 2,254 Net periodic cost (income) 981 (513 ) 622 Other changes in plan assets and benefit obligations recognized as a charge to other comprehensive income (loss) Net loss for the period (83 ) (3,911 ) (9,191 ) Amortization of net loss 3,071 1,909 2,621 Total unrealized gain (loss) 2,988 (2,002 ) (6,570 ) Total recognized in net periodic pension cost and other comprehensive income (loss) $ 2,007 $ (1,489 ) $ (7,192 ) Weighted-average assumptions used to determine the net periodic cost Discount rate 3.86 % 3.99 % 3.60 % Expected return on plan assets 6.25 % 6.50 % 6.50 %
Schedule of Pension Plan Asset Allocation	Pension Plan Asset Allocation (Dollar amounts in thousands) Percentage of Plan Assets as of December 31, Target Allocation Fair Value of Plan Assets (1) 2017 2016 Asset Category Equity securities 50 - 60% $ 39,954 60 % 60 % Fixed income 30 - 48% 22,734 35 % 33 % Cash equivalents 2 - 10% 3,471 5 % 7 % Total $ 66,159 100 % 100 % (1) Additional information regarding the fair value of Pension Plan assets as of December 31, 2017 can be found in Note 21 , " Fair Value ."
Schedule of Estimated Future Pension Benefit Payments	The following table presents estimated future pension benefit payments under the Pension Plan for retirees already receiving benefits and future retirees, assuming they retire and begin receiving unreduced benefits as soon as they are eligible. Estimated Future Pension Benefit Payments (Dollar amounts in thousands) Total Year ending December 31, 2018 $ 6,849 2019 5,462 2020 5,366 2021 5,216 2022 5,064 2023-2026 20,222

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares of Common Stock Available Under Share-Based Plans	Shares of Common Stock Available Under Share-Based Plans As of December 31, 2017 Shares Authorized Shares Available For Grant Omnibus Plan 8,631,641 1,835,929 Directors Plan 481,250 104,782
Nonqualified Stock Option Transactions	Nonqualified Stock Option Transactions (Amounts in thousands, except per share data) Year Ended December 31, 2017 Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (1) Aggregate Intrinsic Value (2) Options outstanding beginning balance 486 $ 31.77 Expired (254 ) 37.78 Options outstanding ending balance 232 $ 25.19 0.75 $ 513 Exercisable at the end of the year 232 $ 25.19 0.75 $ 513 (1) Represents the average remaining contractual life in years. (2) Aggregate intrinsic value represents the total pre-tax intrinsic value that would have been received by the option holders if they had exercised their options on December 31, 2017 . Intrinsic value equals the difference between the Company's average of the high and low stock price on the last trading day of the year and the option exercise price, multiplied by the number of shares. This amount will fluctuate with changes in the fair value of the Company's common stock.
Restricted Stock, Restricted Stock Unit, and Performance Share Award Transactions	Restricted Stock, Restricted Stock Unit, and Performance Share Award Transactions (Amounts in thousands, except per share data) Year Ended December 31, 2017 Restricted Stock/Unit Awards Performance Shares Number of Shares/Units Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Non-vested awards beginning balance 989 $ 16.95 408 $ 15.78 Granted 477 24.71 145 24.71 Vested (367 ) 16.79 (54 ) 16.79 Forfeited (46 ) 19.80 (33 ) 19.80 Non-vested awards ending balance 1,053 $ 20.36 466 $ 18.16
Schedule of Other Share-based Compensation, Activity	Other Restricted Stock, Restricted Stock Unit, and Performance Share Award Information (Amounts in thousands, except per share data) Years Ended December 31, 2017 2016 2015 Weighted-average grant date fair value of restricted stock, restricted stock unit, and performance share awards granted during the year $ 24.71 $ 17.28 $ 16.95 Total fair value of restricted stock, restricted stock unit, and performance share awards vested during the year 13,760 12,231 7,615 Income tax benefit realized from the vesting/release of restricted stock, restricted stock unit, and performance share awards 4,007 2,529 2,368
Effect of Recording Share-Based Compensation Expense	Effect of Recording Share-Based Compensation Expense (Dollar amounts in thousands) Years ended December 31, 2017 2016 2015 Total share-based compensation expense (1) $ 11,223 $ 7,879 $ 7,242 Income tax benefit 4,601 3,152 2,962 Share-based compensation expense, net of tax $ 6,622 $ 4,727 $ 4,280 Unrecognized compensation expense $ 13,266 $ 9,990 $ 8,644 Weighted-average amortization period remaining (in years) 1.3 1.3 1.4 (1) Comprised of restricted stock, restricted stock unit, and performance share awards expense.

Regulatory and Capital Matters

Regulatory and Capital Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Summary of Regulatory Capital Ratios	The following table outlines the Company's and the Bank's measures of capital as of the dates presented and the capital guidelines established by the Federal Reserve for the Company and the Bank to be categorized as adequately capitalized and the Bank to be categorized as "well-capitalized." Summary of Regulatory Capital Ratios (Dollar amounts in thousands) Actual Adequately Capitalized To Be Well-Capitalized Under Prompt Corrective Action Provisions Capital Ratio % Capital Ratio % Capital Ratio % As of December 31, 2017 Total capital to risk-weighted assets: First Midwest Bancorp, Inc. $ 1,448,124 12.15 $ 1,102,634 9.250 N/A N/A First Midwest Bank 1,300,809 10.95 1,099,133 9.250 $ 1,188,252 10.00 Tier 1 capital to risk-weighted assets: First Midwest Bancorp, Inc. 1,204,468 10.10 864,227 7.250 N/A N/A First Midwest Bank 1,204,080 10.13 861,482 7.250 950,601 8.00 CET1 to risk-weighted assets: First Midwest Bancorp, Inc. 1,153,939 9.68 685,421 5.750 N/A N/A First Midwest Bank 1,204,080 10.13 683,245 5.750 772,364 6.50 Tier 1 capital to average assets: First Midwest Bancorp, Inc. 1,204,468 8.99 536,200 4.000 N/A N/A First Midwest Bank 1,204,080 9.10 529,147 4.000 661,434 5.00 As of December 31, 2016 Total capital to risk-weighted assets: First Midwest Bancorp, Inc. $ 1,225,529 12.23 $ 864,176 8.625 N/A N/A First Midwest Bank 1,043,482 10.73 838,741 8.625 $ 972,454 10.00 Tier 1 capital to risk-weighted assets: First Midwest Bancorp, Inc. 991,873 9.90 663,788 6.625 N/A N/A First Midwest Bank 956,399 9.83 644,251 6.625 777,963 8.00 CET1 to risk-weighted assets: First Midwest Bancorp, Inc. 941,315 9.39 513,496 5.125 N/A N/A First Midwest Bank 956,399 9.83 498,383 5.125 632,095 6.50 Tier 1 capital to average assets: First Midwest Bancorp, Inc. 991,873 8.99 441,473 4.000 N/A N/A First Midwest Bank 956,399 8.76 436,560 4.000 545,700 5.00 N/A – Not applicable.

Derivative Instruments and He49

Derivative Instruments and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Interest Rate Derivatives	Cash Flow Hedges (Dollar amounts in thousands) As of December 31, 2017 2016 Gross notional amount outstanding $ 1,960,000 $ 1,470,000 Derivative asset fair value 3,989 5,402 Derivative liability fair value (10,219 ) (7,390 ) Weighted-average interest rate received 1.58 % 1.37 % Weighted-average interest rate paid 1.61 % 1.11 % Weighted-average maturity (in years) 2.25 2.83 Fair Value Hedges (Dollar amounts in thousands) As of December 31, 2017 2016 Gross notional amount outstanding $ 5,458 $ 5,958 Derivative liability fair value (101 ) (282 ) Weighted-average interest rate received 3.38 % 2.63 % Weighted-average interest rate paid 5.96 % 5.96 % Weighted-average maturity (in years) 0.84 1.84 Fair value of derivative (1) $ 110 $ 296 (1) This amount represents the fair value if credit risk related contingent features were triggered.
Schedule of Derivative Instruments	Other Derivative Instruments (Dollar amounts in thousands) As of December 31, 2017 2016 Gross notional amount outstanding $ 2,665,358 $ 1,656,612 Derivative asset fair value 17,079 13,478 Derivative liability fair value (14,930 ) (13,478 ) Fair value of derivative (1) 15,059 13,753 (1) This amount represents the fair value if credit risk related contingent factors were triggered.
Offsetting Assets	The following table presents the fair value of the Company's derivatives and offsetting positions as of December 31, 2017 and 2016 . Fair Value of Offsetting Derivatives (Dollar amounts in thousands) As of December 31, 2017 2016 Assets Liabilities Assets Liabilities Gross amounts recognized $ 21,068 $ 25,250 $ 18,880 $ 21,150 Less: amounts offset in the Consolidated Statements of Financial Condition — — — — Net amount presented in the Consolidated Statements of Financial Condition (1) 21,068 25,250 18,880 21,150 Gross amounts not offset in the Consolidated Statements of Financial Condition: Offsetting derivative positions (16,880 ) (16,880 ) (10,889 ) (10,889 ) Cash collateral pledged — (8,370 ) — (10,261 ) Net credit exposure $ 4,188 $ — $ 7,991 $ — (1) Included in other assets or other liabilities in the Consolidated Statements of Financial Condition.
Offsetting Liabilities	The following table presents the fair value of the Company's derivatives and offsetting positions as of December 31, 2017 and 2016 . Fair Value of Offsetting Derivatives (Dollar amounts in thousands) As of December 31, 2017 2016 Assets Liabilities Assets Liabilities Gross amounts recognized $ 21,068 $ 25,250 $ 18,880 $ 21,150 Less: amounts offset in the Consolidated Statements of Financial Condition — — — — Net amount presented in the Consolidated Statements of Financial Condition (1) 21,068 25,250 18,880 21,150 Gross amounts not offset in the Consolidated Statements of Financial Condition: Offsetting derivative positions (16,880 ) (16,880 ) (10,889 ) (10,889 ) Cash collateral pledged — (8,370 ) — (10,261 ) Net credit exposure $ 4,188 $ — $ 7,991 $ — (1) Included in other assets or other liabilities in the Consolidated Statements of Financial Condition.

Commitments, Guarantees, and 50

Commitments, Guarantees, and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments Disclosure	Contractual or Notional Amounts of Financial Instruments (Dollar amounts in thousands) As of December 31, 2017 2016 Commitments to extend credit: Commercial, industrial, and agricultural $ 1,729,426 $ 1,522,152 Commercial real estate 377,551 397,423 Home equity 514,973 426,384 Other commitments (1) 244,222 214,943 Total commitments to extend credit $ 2,866,172 $ 2,560,902 Letters of credit $ 128,801 $ 100,430 (1) Other commitments includes installment and overdraft protection program commitments.

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	The following table provides the fair value for assets and liabilities required to be measured at fair value on a recurring basis in the Consolidated Statements of Financial Condition by level in the fair value hierarchy. Recurring Fair Value Measurements (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Trading securities: Money market funds $ 1,685 $ — $ — $ 1,645 $ — $ — Mutual funds 18,762 — — 16,275 — — Total trading securities 20,447 — — 17,920 — — Securities available-for-sale: U.S. treasury securities 46,345 — — 48,541 — — U.S. agency securities — 156,847 — — 183,637 — CMOs — 1,095,186 — — 1,047,446 — MBSs — 369,543 — — 332,655 — Municipal securities — 208,991 — — 270,846 — CDOs — — — — — 33,260 Equity securities — 7,297 — — 3,065 — Total securities available-for-sale 46,345 1,837,864 — 48,541 1,837,649 33,260 Mortgage servicing rights ("MSRs") (1) — — 5,894 — — 6,120 Derivative assets (1) — 21,068 — — 18,880 — Liabilities Derivative liabilities (2) $ — $ 25,250 $ — $ — $ 21,150 $ — (1) Included in other assets in the Consolidated Statements of Financial Condition. (2) Included in other liabilities in the Consolidated Statements of Financial Condition.
Significant Unobservable Inputs Used in the Valuation of CDOs	The following table presents the ranges of significant, unobservable inputs calculated using the weighted average of the Issuers used by the Company as of December 31, 2016 . Significant Unobservable Inputs Used in the Valuation of CDOs As of December 31, 2016 Probability of prepayment 0.0 % - 10.9% Probability of default 16.7 % - 46.8% Loss given default 93.3 % - 98.9% Probability of deferral cure 7.6 % - 100.0% The following table presents the ranges of significant, unobservable inputs used by the Company to determine the fair value of MSRs as December 31, 2017 and 2016 . Significant Unobservable Inputs Used in the Valuation of MSRs As of December 31, 2017 2016 Prepayment speed 4.2 % - 13.1% 7.7 % - 22.8% Maturity (months) 6 - 92 12 - 103 Discount rate 9.5 % - 12.0% 9.5 % - 13.0%
Carrying Value of CDOs	A rollforward of the carrying value of CDOs for the three years ended December 31, 2017 is presented in the following table. Carrying Value of CDOs (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 33,260 $ 31,529 $ 33,774 Additions — — — Change in other comprehensive income (loss) (1) 14,421 2,337 (2,030 ) Paydowns and sales (47,681 ) (606 ) (215 ) Ending balance $ — $ 33,260 $ 31,529 (1) Included in unrealized holding gains (losses) in the Consolidated Statements of Comprehensive Income.
Significant Unobservable Inputs Used in the Valuation of MSRs	The following table presents the ranges of significant, unobservable inputs calculated using the weighted average of the Issuers used by the Company as of December 31, 2016 . Significant Unobservable Inputs Used in the Valuation of CDOs As of December 31, 2016 Probability of prepayment 0.0 % - 10.9% Probability of default 16.7 % - 46.8% Loss given default 93.3 % - 98.9% Probability of deferral cure 7.6 % - 100.0% The following table presents the ranges of significant, unobservable inputs used by the Company to determine the fair value of MSRs as December 31, 2017 and 2016 . Significant Unobservable Inputs Used in the Valuation of MSRs As of December 31, 2017 2016 Prepayment speed 4.2 % - 13.1% 7.7 % - 22.8% Maturity (months) 6 - 92 12 - 103 Discount rate 9.5 % - 12.0% 9.5 % - 13.0%
Fair Value Inputs Mortgage Servicing Assets Quantitative Information	A rollforward of the carrying value of MSRs for the three years ended December 31, 2017 is presented in the following table. Carrying Value of MSRs (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Beginning balance $ 6,120 $ 1,853 $ 1,728 Additions from acquisition — 3,092 — New MSRs 673 1,263 342 Total (losses) gains included in earnings (1) : Changes in valuation inputs and assumptions (41 ) 610 (11 ) Other changes in fair value (2) (858 ) (698 ) (206 ) Ending balance (3) $ 5,894 $ 6,120 $ 1,853 Contractual servicing fees earned during the year (1) $ 1,536 $ 1,312 $ 546 Total amount of loans being serviced for the benefit of others at the end of the year 607,016 640,530 242,915 (1) Included in mortgage banking income in the Consolidated Statements of Income and related to assets held as of December 31, 2017 , 2016 , and 2015 . (2) Primarily represents changes in expected future cash flows over time due to payoffs and paydowns. (3) Included in other assets in the Consolidated Statements of Financial Condition.
Fair Value Assets Measured On Annual Basis	The fair value of Pension Plan assets is presented in the following table by level in the fair value hierarchy. Annual Fair Value Measurements for Pension Plan Assets (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Level 1 Level 2 Total Level 1 Level 2 Total Pension plan assets: Mutual funds (1) $ 41,002 $ — $ 41,002 $ 29,071 $ — $ 29,071 U.S. government and government agency securities 3,678 9,397 13,075 5,957 7,947 13,904 Corporate bonds — 9,171 9,171 — 7,010 7,010 Common stocks — — — 7,526 — 7,526 Common trust funds — 2,911 2,911 — 7,678 7,678 Total pension plan assets $ 44,680 $ 21,479 $ 66,159 $ 42,554 $ 22,635 $ 65,189 (1) Includes mutual funds, money market funds, cash, cash equivalents, and accrued interest.
Fair Value Measurements, Nonrecurring	The following table provides the fair value for each class of assets and liabilities required to be measured at fair value on a non-recurring basis in the Consolidated Statements of Financial Condition by level in the fair value hierarchy. Non-Recurring Fair Value Measurements (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Collateral-dependent impaired loans (1) $ — $ — $ 33,240 $ — $ — $ 22,019 OREO (2) — — 12,340 — — 8,624 Loans held-for-sale (3) — — 21,098 — — 10,484 Assets held-for-sale (4) — — 2,208 — — 4,075 (1) Includes impaired loans with charge-offs and impaired loans with a specific reserve during the periods presented. (2) Includes OREO with fair value adjustments subsequent to initial transfer that occurred during the periods presented. (3) Included in other assets in the Consolidated Statements of Financial Condition. (4) Included in premises, furniture, and equipment in the Consolidated Statements of Financial Condition.
Fair Value, by Balance Sheet Grouping	For certain financial instruments that are not required to be measured at fair value in the Consolidated Statements of Financial Condition, the Company must disclose the estimated fair values and the level within the fair value hierarchy as shown in the following table. Fair Value Measurements of Other Financial Instruments (Dollar amounts in thousands) As of December 31, 2017 As of December 31, 2016 Fair Value Hierarchy Carrying Fair Value Carrying Fair Value Assets Cash and due from banks 1 $ 192,800 $ 192,800 $ 155,055 $ 155,055 Interest-bearing deposits in other banks 2 153,770 153,770 107,093 107,093 Securities held-to-maturity 2 13,760 12,013 22,291 18,212 FHLB and FRB stock 2 69,708 69,708 59,131 59,131 Loans 3 10,345,397 10,059,992 8,172,584 7,973,845 Investment in BOLI 3 279,900 279,900 219,746 219,746 Accrued interest receivable 3 45,261 45,261 34,384 34,384 Other interest-earning assets 3 228 228 834 834 Liabilities Deposits 2 $ 11,053,325 $ 11,038,819 $ 8,828,603 $ 8,820,572 Borrowed funds 2 714,884 714,884 879,008 879,008 Senior and subordinated debt 2 195,170 198,806 194,603 197,888 Accrued interest payable 2 4,704 4,704 3,416 3,416

Condensed Parent Company Fina52

Condensed Parent Company Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Statements of Financial Condition - Parent Company Only	The following represents the condensed financial statements of First Midwest Bancorp, Inc., the Parent Company. Statements of Financial Condition (Parent Company only) (Dollar amounts in thousands) As of December 31, 2017 2016 Assets Cash and due from banks $ 120,812 $ 140,217 Investments in and advances to subsidiaries 1,952,414 1,279,065 Other assets 43,606 139,060 Total assets $ 2,116,832 $ 1,558,342 Liabilities and Stockholders' Equity Senior and subordinated debt $ 195,170 $ 194,603 Accrued interest payable and other liabilities 56,788 106,659 Stockholders' equity 1,864,874 1,257,080 Total liabilities and stockholders' equity $ 2,116,832 $ 1,558,342
Statements of Income - Parent Company Only	Statements of Income (Parent Company only) (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Income Dividends from subsidiaries $ 74,091 $ 86,791 $ 127,000 Interest income 2,211 2,188 2,164 Securities transactions and other (1,372 ) 215 584 Total income 74,930 89,194 129,748 Expenses Interest expense 12,428 12,477 12,545 Salaries and employee benefits 20,978 16,104 14,624 Other expenses 9,126 7,110 6,003 Total expenses 42,532 35,691 33,172 Income before income tax benefit and equity in undistributed income (loss) of subsidiaries 32,398 53,503 96,576 Income tax benefit 14,851 12,878 11,950 Income before equity in undistributed income (loss) of subsidiaries 47,249 66,381 108,526 Equity in undistributed income (loss) of subsidiaries 51,138 25,968 (26,462 ) Net income 98,387 92,349 82,064 Net income applicable to non-vested restricted shares (916 ) (1,043 ) (882 ) Net income applicable to common shares $ 97,471 $ 91,306 $ 81,182
Statements of Cash Flows - Parent Company Only	Statements of Cash Flows (Parent Company only) (Dollar amounts in thousands) Years Ended December 31, 2017 2016 2015 Operating Activities Net income $ 98,387 $ 92,349 $ 82,064 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed (income) loss of subsidiaries (51,138 ) (25,968 ) 26,462 Depreciation of premises, furniture, and equipment 9 2 7 Net securities losses (gains) 1,523 — (1 ) Share-based compensation expense 11,223 7,879 7,242 Tax benefit (expense) related to share-based compensation 349 (197 ) (406 ) Net decrease (increase) in other assets 18,667 (75,104 ) 23,699 Net (decrease) increase in other liabilities (52,377 ) 74,571 (17,132 ) Net cash provided by operating activities 26,643 73,532 121,935 Investing Activities Purchases of securities available-for-sale — (14 ) — Proceeds from sales and maturities of securities available-for-sale 42,516 601 310 Purchase of premises, furniture, and equipment (119 ) — (5 ) Net cash paid for acquisitions (47,364 ) (14,905 ) (16,047 ) Net cash used in investing activities (4,967 ) (14,318 ) (15,742 ) Financing Activities Net proceeds from the issuance of subordinated debt — 146,484 — Payments for the retirement of senior and subordinated debt — (153,500 ) — Treasury stock activity — — (120 ) Cash dividends paid (37,129 ) (29,198 ) (27,036 ) Restricted stock activity (3,952 ) (2,476 ) (2,890 ) Net cash used in financing activities (41,081 ) (38,690 ) (30,046 ) Net (decrease) increase in cash and cash equivalents (19,405 ) 20,524 76,147 Cash and cash equivalents at beginning of year 140,217 119,693 43,546 Cash and cash equivalents at end of year $ 120,812 $ 140,217 $ 119,693 Supplemental Disclosures of Cash Flow Information: Common stock issued for acquisitions, net of issuance costs $ 534,090 $ 54,896 $ —

Summary of Significant Accoun53

Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2017segmentsubsidiary
Property, Plant and Equipment [Line Items]
Number of wholly-owned subsidiaries | subsidiary	3
Number of reportable segments | segment	1
Finite-lived intangible assets amortization period	13 years
Furniture And Equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Furniture And Equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Premises | Minimum
Property, Plant and Equipment [Line Items]
Useful life	25 years
Premises | Maximum
Property, Plant and Equipment [Line Items]
Useful life	40 years

Recent Accounting Pronounceme54

Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 27, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Tax benefit to the provision for income tax expense		$ 638
Deferred gain, net		$ 74,600	$ 81,000	$ 82,500
Early adopted | Subsequent Event | Accounting Standards Update 2018-02
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification of tax effects from AOCI to retained earnings	$ 6,900

Acquisitions - Narrative (Deta

Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands	Jan. 06, 2017USD ($)$ / sharesshares	Mar. 08, 2016USD ($)locationshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Feb. 28, 2017USD ($)	Dec. 31, 2014USD ($)
Business Acquisition [Line Items]
Goodwill			$ 697,608	$ 340,879	$ 319,007		$ 310,589
Acquisition and integration related expenses			20,123	14,352	$ 1,389
Standard Bancshares, Inc.
Business Acquisition [Line Items]
Fixed exchange ratio (in shares) | shares	0.4350
Consideration transferred	$ 580,715
Common stock, shares issued (in shares) | shares	21,057,085
Cash paid	$ 47,125
Goodwill	$ 345,334
Goodwill adjustment			6,000
Acquisition and integration related expenses			19,100	$ 8,000
Premier Asset Management LLC
Business Acquisition [Line Items]
Assets under management acquired						$ 550,000
NI Bancshares Corporation
Business Acquisition [Line Items]
Consideration transferred		$ 70,082
Common stock, shares issued (in shares) | shares		3,042,494
Cash paid		$ 15,186
Goodwill		$ 22,174
Goodwill adjustment			$ 423
Number of retail branches acquired | location		10
Minimum value of trust assets under management acquired		$ 700,000
First Midwest Bancorp, Inc.
Business Acquisition [Line Items]
Share price (in dollars per share) | $ / shares	$ 25.34
Standard Bancshares, Inc.
Business Acquisition [Line Items]
Share price (in dollars per share) | $ / shares	$ 11.02

Acquisitions - Acquisition Act

Acquisitions - Acquisition Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 06, 2017	Mar. 08, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Goodwill			$ 697,608	$ 340,879	$ 319,007	$ 310,589
Liabilities
Intangible liabilities			$ 6,913
Standard Bancshares, Inc.
Assets
Cash and due from banks and interest-bearing deposits in other banks	$ 102,149
Securities available-for-sale	214,107
Securities held-to-maturity	0
FHLB and FRB stock	3,247
Loans	1,762,303
OREO	8,424
Investment in BOLI	55,629
Goodwill	345,334
Other intangible assets	31,072
Premises, furniture, and equipment	56,517
Accrued interest receivable and other assets	60,278
Total assets	2,639,060
Liabilities
Noninterest-bearing deposits	675,354
Interest-bearing deposits	1,348,520
Total deposits	2,023,874
Borrowed funds	0
Intangible liabilities	0
Accrued interest payable and other liabilities	34,471
Total liabilities	2,058,345
Consideration Paid
Common stock (2017 - 21,057,085 share issued at $25.34 per share, 2016 - 3,042,494 shares issued at $18.059 per share), net of issuance costs	533,590
Cash paid	47,125
Total consideration paid	$ 580,715
Common stock, shares issued (in shares)	21,057,085
Shares issued (in dollars per share)	$ 25.34
NI Bancshares Corporation
Assets
Cash and due from banks and interest-bearing deposits in other banks		$ 72,533
Securities available-for-sale		125,843
Securities held-to-maturity		1,864
FHLB and FRB stock		1,549
Loans		396,181
OREO		2,863
Investment in BOLI		8,384
Goodwill		22,174
Other intangible assets		10,408
Premises, furniture, and equipment		19,636
Accrued interest receivable and other assets		16,453
Total assets		677,888
Liabilities
Noninterest-bearing deposits		130,909
Interest-bearing deposits		464,012
Total deposits		594,921
Borrowed funds		2,416
Intangible liabilities		230
Accrued interest payable and other liabilities		10,239
Total liabilities		607,806
Consideration Paid
Common stock (2017 - 21,057,085 share issued at $25.34 per share, 2016 - 3,042,494 shares issued at $18.059 per share), net of issuance costs		54,896
Cash paid		15,186
Total consideration paid		$ 70,082
Common stock, shares issued (in shares)		3,042,494
Shares issued (in dollars per share)		$ 18.059

Acquisitions - Unaudited Pro F

Acquisitions - Unaudited Pro Forma Combined Results of Operations (Details) - Standard Bancshares, Inc. - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Total revenues	[1]	$ 636,762	$ 616,922
Net income		$ 109,195	$ 108,770
[1]	(1) Includes net interest income and total noninterest income.

Acquisitions - Standard Acquir

Acquisitions - Standard Acquired Loans (Details) - Standard Bancshares, Inc. - Acquired loans $ in Thousands	Jan. 06, 2017USD ($)
Business Acquisition [Line Items]
Fair value	$ 1,636,921
Contractually required principal and interest payments	1,930,311
Best estimate of contractual cash flows not expected to be collected	100,469	[1]
Best estimate of contractual cash flows expected to be collected	1,829,842
PCI
Business Acquisition [Line Items]
Fair value	125,382
Contractually required principal and interest payments	218,680
Best estimate of contractual cash flows not expected to be collected	65,610	[1]
Best estimate of contractual cash flows expected to be collected	$ 153,070
[1]	(1) Includes interest payments not expected to be collected due to loan prepayments as well as principal and interest payments not expected to be collected due to customer default.

Securities - Securities Portfo

Securities - Securities Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	$ 13,760	$ 22,291
Fair Value	12,013	18,212
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	20,447	17,920
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	1,907,826	1,957,584
Gross Unrealized Gains	1,406	4,562
Gross Unrealized Losses	(25,023)	(42,696)
Fair Value	1,884,209	1,919,450
U.S. treasury securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	46,529	48,581
Gross Unrealized Gains	0	26
Gross Unrealized Losses	(184)	(66)
Fair Value	46,345	48,541
U.S. agency securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	157,636	183,528
Gross Unrealized Gains	197	519
Gross Unrealized Losses	(986)	(410)
Fair Value	156,847	183,637
Collateralized mortgage obligations (CMOs)
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	1,113,019	1,064,130
Gross Unrealized Gains	121	969
Gross Unrealized Losses	(17,954)	(17,653)
Fair Value	1,095,186	1,047,446
Other mortgage-backed securities (MBSs)
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	373,676	337,139
Gross Unrealized Gains	201	1,395
Gross Unrealized Losses	(4,334)	(5,879)
Fair Value	369,543	332,655
Municipal securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	209,558	273,319
Gross Unrealized Gains	693	1,245
Gross Unrealized Losses	(1,260)	(3,718)
Fair Value	208,991	270,846
Trust-preferred collateralized debt obligations (CDOs)
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	0	47,681
Gross Unrealized Gains	0	261
Gross Unrealized Losses	0	(14,682)
Fair Value	0	33,260
Equity securities
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	7,408	3,206
Gross Unrealized Gains	194	147
Gross Unrealized Losses	(305)	(288)
Fair Value	7,297	3,065
Trading securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	20,447	17,920
Municipal securities
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	13,760	22,291
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,747)	(4,079)
Fair Value	$ 12,013	$ 18,212

Securities - Remaining Contrac

Securities - Remaining Contractual Maturity of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-Sale Securities, Amortized Cost Basis [Abstract]
One year or less	$ 87,379
After one year to five years	323,203
After five years to ten years	3,141
After ten years	0
Securities that do not have a single contractual maturity date	1,494,103
Amortized Cost	1,907,826	$ 1,957,584
Available-for-Sale Securities, Fair Value [Abstract]
One year or less	87,053
After one year to five years	322,000
After five years to ten years	3,130
After ten years	0
Securities that do not have a single contractual maturity date	1,472,026
Total	1,884,209	1,919,450
Held-to-Maturity Securities, Amortized Cost [Abstract]
One year or less	1,432
After one year to five years	5,831
After five years to ten years	2,243
After ten years	4,254
Securities that do not have a single contractual maturity date	0
Amortized Cost	13,760	22,291
Held-to-Maturity Securities, Fair Value [Abstract]
One year or less	1,250
After one year to five years	5,090
After five years to ten years	1,959
After ten years	3,714
Securities that do not have a single contractual maturity date	0
Total	$ 12,013	$ 18,212

Securities - Narrative (Detail

Securities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-Sale Securities [Line Items]
Available-for-sale securities pledged as collateral	$ 1,100,000,000	$ 1,100,000,000
Held-to-maturity securities pledged as collateral	0	0
Net realized (losses) gains on sales of securities	1,876,000	(1,420,000)	$ (2,373,000)
CMOs
Schedule of Available-for-Sale Securities [Line Items]
Net realized (losses) gains on sales of securities	2,800,000
CDOs
Schedule of Available-for-Sale Securities [Line Items]
Net realized (losses) gains on sales of securities	404,000
Municipal securities
Schedule of Available-for-Sale Securities [Line Items]
Net realized (losses) gains on sales of securities	(854,000)	(1,100,000)
MBS and equity securities
Schedule of Available-for-Sale Securities [Line Items]
Net realized (losses) gains on sales of securities	$ (449,000)
Equity securities
Schedule of Available-for-Sale Securities [Line Items]
Net realized (losses) gains on sales of securities		$ (304,000)
MBSs
Schedule of Available-for-Sale Securities [Line Items]
Net realized (losses) gains on sales of securities			(1,900,000)
CMOs, municipal securities, and other investments
Schedule of Available-for-Sale Securities [Line Items]
Net realized (losses) gains on sales of securities			$ (521,000)

Securities - Securities (Losse

Securities - Securities (Losses) Gains (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gains (losses) on sales of securities:
Gross realized gains	$ 5,478	$ 1,589	$ 2,519
Gross realized losses	(7,354)	(169)	(146)
Net realized (losses) gains on sales of securities	(1,876)	1,420	2,373
Non-cash impairment charges:
OTTI	0	0	0
Net realized (losses) gains	$ (1,876)	$ 1,420	$ 2,373

Securities - Changes In Credit

Securities - Changes In Credit Losses Recognized In Earnings (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)security
Changes in Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance		$ 23,345	$ 23,345	$ 23,516
OTTI included in earnings:
Losses on securities that previously had OTTI	[1]	0	0	0
Losses on securities that did not previously have OTTI	[1]	0	0	0
Reduction for securities sales	[1],[2]	(23,345)	0	(171)
Ending balance		0	$ 23,345	23,345
CDOs
OTTI included in earnings:
Reduction for securities sales		$ (47,700)
Number of CDOs sold (security) | security		11
CMOs
OTTI included in earnings:
Reduction for securities sales				$ (1,300)
Number of CMOs sold (security) | security				1
[1]	Included in net securities (losses) gains in the Consolidated Statements of Income.
[2]	These reductions were driven by the sale of 11 CDOs with a carrying value of $47.7 million during the year ended December 31, 2017 and one CMO with a carrying value of $1.3 million during the year ended December 31, 2015.

Securities - Securities In An

Securities - Securities In An Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)security
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security	656	695
Fair Value - Less Than 12 Months	$ 613,975	$ 974,337
Unrealized Losses - Less Than 12 Months	5,247	18,720
Fair Value - 12 Months or Longer	1,015,438	567,538
Unrealized Losses - 12 Months or Longer	19,776	23,976
Fair Value - Total	1,629,413	1,541,875
Unrealized Losses - Total	$ 25,023	$ 42,696
U.S. treasury securities
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security	20	16
Fair Value - Less Than 12 Months	$ 19,918	$ 33,505
Unrealized Losses - Less Than 12 Months	87	61
Fair Value - 12 Months or Longer	26,427	3,995
Unrealized Losses - 12 Months or Longer	97	5
Fair Value - Total	46,345	37,500
Unrealized Losses - Total	$ 184	$ 66
U.S. agency securities
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security	72	28
Fair Value - Less Than 12 Months	$ 66,899	$ 62,064
Unrealized Losses - Less Than 12 Months	300	364
Fair Value - 12 Months or Longer	58,021	11,814
Unrealized Losses - 12 Months or Longer	686	46
Fair Value - Total	124,920	73,878
Unrealized Losses - Total	$ 986	$ 410
CMOs
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security	211	194
Fair Value - Less Than 12 Months	$ 365,131	$ 523,233
Unrealized Losses - Less Than 12 Months	3,265	10,309
Fair Value - 12 Months or Longer	633,227	411,758
Unrealized Losses - 12 Months or Longer	14,689	7,344
Fair Value - Total	998,358	934,991
Unrealized Losses - Total	$ 17,954	$ 17,653
MBSs
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security	86	68
Fair Value - Less Than 12 Months	$ 126,136	$ 221,174
Unrealized Losses - Less Than 12 Months	902	4,726
Fair Value - 12 Months or Longer	210,017	77,780
Unrealized Losses - 12 Months or Longer	3,432	1,154
Fair Value - Total	336,153	298,954
Unrealized Losses - Total	$ 4,334	$ 5,880
Municipal securities
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security	265	380
Fair Value - Less Than 12 Months	$ 35,500	$ 133,957
Unrealized Losses - Less Than 12 Months	479	3,059
Fair Value - 12 Months or Longer	81,360	29,280
Unrealized Losses - 12 Months or Longer	781	659
Fair Value - Total	116,860	163,237
Unrealized Losses - Total	$ 1,260	$ 3,718
CDOs
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security		7
Fair Value - Less Than 12 Months		$ 0
Unrealized Losses - Less Than 12 Months		0
Fair Value - 12 Months or Longer		30,592
Unrealized Losses - 12 Months or Longer		14,682
Fair Value - Total		30,592
Unrealized Losses - Total		$ 14,682
Equity securities
Securities in An Unrealized Loss Position [Line Items]
Number of Securities | security	2	2
Fair Value - Less Than 12 Months	$ 391	$ 404
Unrealized Losses - Less Than 12 Months	214	201
Fair Value - 12 Months or Longer	6,386	2,319
Unrealized Losses - 12 Months or Longer	91	86
Fair Value - Total	6,777	2,723
Unrealized Losses - Total	$ 305	$ 287
Municipal securities
Schedule of Held-to-Maturity Securities [Line Items]
Number of Securities | security	8	14
Fair Value - Less than 12 Months	$ 0	$ 0
Unrealized Losses - Less than 12 Months	0	0
Fair Value - 12 Months or Longer	12,013	18,212
Unrealized Losses - 12 Months or Longer	1,747	4,079
Fair Value - Total	12,013	18,212
Unrealized Losses - Total	$ 1,747	$ 4,079

Loans - Loan Portfolio (Detail

Loans - Loan Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 10,437,812	$ 8,254,145
Deferred loan fees included in total loans	4,986	3,838
Overdrawn demand deposits included in total loans	8,587	7,836
Commercial, industrial, and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,960,800	3,217,154
Commercial, industrial, and agricultural | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,529,914	2,827,658
Total loans	3,529,914	2,827,658
Commercial, industrial, and agricultural | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	430,886	389,496
Total loans	430,886	389,496
Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,553,618	3,627,087
Total loans	4,553,618	3,627,087
Commercial real estate loans | Office, retail, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,979,820	1,581,967
Total loans	1,979,820	1,581,967
Commercial real estate loans | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	675,463	614,052
Total loans	675,463	614,052
Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	539,820	451,540
Total loans	539,820	451,540
Commercial real estate loans | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,358,515	979,528
Total loans	1,358,515	979,528
Total corporate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,514,418	6,844,241
Total loans	8,514,418	6,844,241
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,923,394	1,409,904
Total loans	1,923,394	1,409,904
Consumer loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	827,055	747,983
Total loans	827,055	747,983
Consumer loans | 1-4 family mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	774,357	423,922
Total loans	774,357	423,922
Consumer loans | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	321,982	237,999
Total loans	$ 321,982	$ 237,999

Loans - Carrying Value of Loan

Loans - Carrying Value of Loans Pledged (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loans pledged to secure:
FHLB advances (blanket pledge)	$ 4,587,240	$ 3,667,202
FRB's Discount Window Primary Credit Program	1,099,712	777,950
Total	$ 5,686,952	$ 4,445,152

Loans - Loans Sales (Details)

Loans - Loans Sales (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total net gains on loan sales		$ 7,078	$ 8,931	$ 6,847
Corporate loan sales
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales		52,974	54,681	31,091
Less book value of loans sold		51,781	52,821	29,535
Total net gains on loan sales	[1]	1,193	1,860	1,556
1-4 family mortgage loan sales
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales		258,626	290,383	185,308
Less book value of loans sold		252,741	283,312	180,017
Total net gains on loan sales	[2]	$ 5,885	$ 7,071	$ 5,291
[1]	Net gains on corporate loan sales are included in other service charges, commissions, and fees in the Consolidated Statements of Income.
[2]	Net gains on mortgage loan sales are included in mortgage banking income in the Consolidated Statements of Income.

Loans - Narrative (Details)

Loans - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Eligible borrowing capacity in FHLB advances	$ 2,600,000	$ 2,000,000
FRBs Discount Window Primary Credit Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Eligible borrowing capacity through FRB's Discount Window Primary Credit Program	$ 843,618	$ 629,699

Acquired and Covered Loans - N

Acquired and Covered Loans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Non-residential mortgage loans with expired loss share agreements	$ 12.7	$ 14.9
Outstanding balance of PCI loans	210.7	84.8
Renewed non-purchased credit impaired loans	366	117.6
Acquired and Covered Receivables
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Accretion on acquired loans	$ 33.9	$ 14.6	$ 16.3

Acquired and Covered Loans - A

Acquired and Covered Loans - Acquired and Covered Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Acquired Loans [Line Items]
Non-PCI	$ 1,524,453	$ 628,718
Total	1,661,906	690,385
Acquired loans
Acquired Loans [Line Items]
Non-PCI	1,512,664	613,339
Total	1,643,358	667,111
Covered loans
Acquired Loans [Line Items]
Non-PCI	11,789	15,379
Total	18,548	23,274
Receivables acquired with deteriorated credit quality
Acquired Loans [Line Items]
PCI	137,453	61,667
Receivables acquired with deteriorated credit quality | Acquired loans
Acquired Loans [Line Items]
PCI	130,694	53,772
Receivables acquired with deteriorated credit quality | Covered loans
Acquired Loans [Line Items]
PCI	$ 6,759	$ 7,895

Acquired and Covered Loans - C

Acquired and Covered Loans - Changes in FDIC Indemnification Asset (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
FDIC Indemnification Asset [Roll Forward]
Beginning balance	$ 4,522	$ 3,903	$ 8,452
Amortization	(1,208)	(1,185)	(1,461)
Change in expected reimbursements from the FDIC for changes in expected credit losses	(792)	330	1,313
Net payments to (from) the FDIC	792	1,474	(4,401)
Ending balance	$ 3,314	$ 4,522	$ 3,903

Acquired and Covered Loans -72

Acquired and Covered Loans - Changes in Accretable Yield (Details) - Receivables acquired with deteriorated credit quality - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Accretable Yield [Roll Forward]
Beginning balance		$ 19,386	$ 24,912	$ 28,244
Additions		27,316	3,981	1,168
Accretion		(15,529)	(8,063)	(11,311)
Other	[1]	1,784	(1,444)	6,811
Ending balance		$ 32,957	$ 19,386	$ 24,912
[1]	Increases represent a rise in the expected future cash flows to be collected over the remaining estimated life of the underlying portfolio while decreases result from the resolution of certain loans occurring earlier than anticipated.

Past Due Loans, Allowance For73

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Aging Analysis of Past Due Loans and Non-Performing Loans by Class (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	$ 10,365,369	$ 8,204,440
Past Due		72,443	49,705
Total loans		10,437,812	8,254,145
Non-accrual	[2]	66,924	59,289
90 Days or More Past Due, Still Accruing Interest		3,555	5,009
Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		137,453	61,667
Receivables acquired with deteriorated credit quality | Non-accrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		763	681
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		52,570	22,923
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		19,873	26,782
Commercial, industrial, and agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		3,960,800	3,217,154
Commercial, industrial, and agricultural | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		12,702	3,182
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	3,490,783	2,816,442
Past Due		39,131	11,216
Total loans		3,529,914	2,827,658
Non-accrual	[2]	40,580	29,938
90 Days or More Past Due, Still Accruing Interest		1,830	374
Commercial, industrial, and agricultural | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	430,221	388,596
Past Due		665	900
Total loans		430,886	389,496
Non-accrual	[2]	219	181
90 Days or More Past Due, Still Accruing Interest		177	736
Commercial, industrial, and agricultural | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		34,620	6,426
Commercial, industrial, and agricultural | 30-89 Days Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		280	0
Commercial, industrial, and agricultural | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		4,511	4,790
Commercial, industrial, and agricultural | 90 Days or More Past Due | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		385	900
Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	4,534,968	3,601,955
Past Due		18,650	25,132
Total loans		4,553,618	3,627,087
Non-accrual	[2]	15,767	20,766
90 Days or More Past Due, Still Accruing Interest		1,053	3,259
Commercial real estate loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		102,813	41,461
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,970,564	1,564,007
Past Due		9,256	17,960
Total loans		1,979,820	1,581,967
Non-accrual	[2]	11,560	17,277
90 Days or More Past Due, Still Accruing Interest		345	1,129
Commercial real estate loans | Office, retail, and industrial | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		14,575	12,446
Commercial real estate loans | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	672,098	612,446
Past Due		3,365	1,606
Total loans		675,463	614,052
Non-accrual	[2]	377	311
90 Days or More Past Due, Still Accruing Interest		20	604
Commercial real estate loans | Multi-family | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		14,071	12,225
Commercial real estate loans | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	539,043	450,927
Past Due		777	613
Total loans		539,820	451,540
Non-accrual	[2]	209	286
90 Days or More Past Due, Still Accruing Interest		371	0
Commercial real estate loans | Construction | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		8,843	4,448
Commercial real estate loans | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,353,263	974,575
Past Due		5,252	4,953
Total loans		1,358,515	979,528
Non-accrual	[2]	3,621	2,892
90 Days or More Past Due, Still Accruing Interest		317	1,526
Commercial real estate loans | Other commercial real estate | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		65,324	12,342
Commercial real estate loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		9,016	7,824
Commercial real estate loans | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		3,156	5,327
Commercial real estate loans | 30-89 Days Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		3,117	858
Commercial real estate loans | 30-89 Days Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		198	332
Commercial real estate loans | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,545	1,307
Commercial real estate loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		9,634	17,308
Commercial real estate loans | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		6,100	12,633
Commercial real estate loans | 90 Days or More Past Due | Multi-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		248	748
Commercial real estate loans | 90 Days or More Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		579	281
Commercial real estate loans | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,707	3,646
Total corporate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	8,455,972	6,806,993
Past Due		58,446	37,248
Total loans		8,514,418	6,844,241
Non-accrual	[2]	56,566	50,885
90 Days or More Past Due, Still Accruing Interest		3,060	4,369
Total corporate loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		115,515	44,643
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		43,916	14,250
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		14,530	22,998
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	1,909,397	1,397,447
Past Due		13,997	12,457
Total loans		1,923,394	1,409,904
Non-accrual	[2]	10,358	8,404
90 Days or More Past Due, Still Accruing Interest		495	640
Consumer loans | Receivables acquired with deteriorated credit quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
PCI		21,938	17,024
Consumer loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	820,099	740,919
Past Due		6,956	7,064
Total loans		827,055	747,983
Non-accrual	[2]	5,946	5,465
90 Days or More Past Due, Still Accruing Interest		98	109
Consumer loans | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	770,120	420,264
Past Due		4,237	3,658
Total loans		774,357	423,922
Non-accrual	[2]	4,412	2,939
90 Days or More Past Due, Still Accruing Interest		0	272
Consumer loans | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	[1]	319,178	236,264
Past Due		2,804	1,735
Total loans		321,982	237,999
Non-accrual	[2]	0	0
90 Days or More Past Due, Still Accruing Interest		397	259
Consumer loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		8,654	8,673
Consumer loans | 30-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		4,102	4,545
Consumer loans | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,145	2,652
Consumer loans | 30-89 Days Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,407	1,476
Consumer loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		5,343	3,784
Consumer loans | 90 Days or More Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,854	2,519
Consumer loans | 90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		2,092	1,006
Consumer loans | 90 Days or More Past Due | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		$ 397	$ 259
[1]	PCI loans with an accretable yield are considered current.
[2]	Includes PCI loans of $763,000 and $681,000 as of December 31, 2017 and December 31, 2016, respectively, which no longer have an accretable yield as estimates of expected future cash flows have decreased since the acquisition due to credit deterioration.

Past Due Loans, Allowance For74

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	$ 87,083	$ 74,855	$ 74,510
Charge-offs	(30,823)	(23,293)	(26,917)
Recoveries	9,179	4,763	6,701
Net charge-offs	(21,644)	(18,530)	(20,216)
Provision for loan losses and other	31,290	30,758	20,561
Ending Balance	96,729	87,083	74,855
Reserve for Unfunded Commitments
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	1,000	1,225	1,816
Charge-offs	0	0	0
Recoveries	0	0	0
Net charge-offs	0	0	0
Provision for loan losses and other	0	(225)	(591)
Ending Balance	1,000	1,000	1,225
Commercial, Industrial, and Agricultural
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	40,709	37,074	31,177
Charge-offs	(22,885)	(9,982)	(16,422)
Recoveries	4,150	2,451	2,588
Net charge-offs	(18,735)	(7,531)	(13,834)
Provision for loan losses and other	33,817	11,166	19,731
Ending Balance	55,791	40,709	37,074
Commercial Real Estate Loans
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	32,039
Ending Balance	23,392	32,039
Commercial Real Estate Loans | Office, Retail, and Industrial
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	17,595	13,124	13,053
Charge-offs	(190)	(4,707)	(2,899)
Recoveries	2,935	337	534
Net charge-offs	2,745	(4,370)	(2,365)
Provision for loan losses and other	(9,344)	8,841	2,436
Ending Balance	10,996	17,595	13,124
Commercial Real Estate Loans | Multi-family
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	3,261	2,469	2,387
Charge-offs	0	(307)	(568)
Recoveries	39	97	15
Net charge-offs	39	(210)	(553)
Provision for loan losses and other	(766)	1,002	635
Ending Balance	2,534	3,261	2,469
Commercial Real Estate Loans | Construction
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	3,444	1,440	3,031
Charge-offs	(38)	(134)	(139)
Recoveries	270	56	350
Net charge-offs	232	(78)	211
Provision for loan losses and other	(195)	2,082	(1,802)
Ending Balance	3,481	3,444	1,440
Commercial Real Estate Loans | Other Commercial Real Estate
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	7,739	6,109	9,019
Charge-offs	(755)	(2,932)	(2,678)
Recoveries	244	524	2,031
Net charge-offs	(511)	(2,408)	(647)
Provision for loan losses and other	(847)	4,038	(2,263)
Ending Balance	6,381	7,739	6,109
Consumer Loans
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	13,335
Ending Balance	16,546	13,335
Consumer Loans | Consumer Loans
Allowance for Credit Losses by Portfolio Segment [Roll Forward]
Beginning balance	13,335	13,414	14,027
Charge-offs	(6,955)	(5,231)	(4,211)
Recoveries	1,541	1,298	1,183
Net charge-offs	(5,414)	(3,933)	(3,028)
Provision for loan losses and other	8,625	3,854	2,415
Ending Balance	$ 16,546	$ 13,335	$ 13,414

Past Due Loans, Allowance For75

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Loans and Related Allowance for Credit Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	$ 51,617	$ 42,650
Loans Collectively Evaluated for Impairment	10,248,742	8,149,828
Loans	10,437,812	8,254,145
Allowance for Credit Losses Individually Evaluated for Impairment	10,074	525
Allowance for Credit Losses Collectively Evaluated for Impairment	82,341	81,864
Total Allowance for Credit Losses	96,729	87,083	$ 74,855	$ 74,510
PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	137,453	61,667
Total Allowance for Credit Losses	4,314	4,694
Reserve for unfunded commitments
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	0	0
Loans Collectively Evaluated for Impairment	0	0
Loans	0	0
Allowance for Credit Losses Individually Evaluated for Impairment	0	0
Allowance for Credit Losses Collectively Evaluated for Impairment	1,000	1,000
Total Allowance for Credit Losses	1,000	1,000	1,225	1,816
Reserve for unfunded commitments | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	0	0
Total Allowance for Credit Losses	0	0
Commercial, industrial, and agricultural
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	38,718	24,645
Loans Collectively Evaluated for Impairment	3,909,380	3,189,327
Loans	3,960,800	3,217,154
Allowance for Credit Losses Individually Evaluated for Impairment	10,074	507
Allowance for Credit Losses Collectively Evaluated for Impairment	45,293	39,554
Total Allowance for Credit Losses	55,791	40,709	37,074	31,177
Commercial, industrial, and agricultural | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	12,702	3,182
Total Allowance for Credit Losses	424	648
Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	12,899	18,005
Loans Collectively Evaluated for Impairment	4,437,906	3,567,621
Loans	4,553,618	3,627,087
Allowance for Credit Losses Individually Evaluated for Impairment	0	18
Allowance for Credit Losses Collectively Evaluated for Impairment	20,515	29,100
Total Allowance for Credit Losses	23,392	32,039
Commercial real estate loans | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	102,813	41,461
Total Allowance for Credit Losses	2,877	2,921
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	10,810	16,287
Loans Collectively Evaluated for Impairment	1,954,435	1,553,234
Loans	1,979,820	1,581,967
Allowance for Credit Losses Individually Evaluated for Impairment	0	0
Allowance for Credit Losses Collectively Evaluated for Impairment	9,333	16,148
Total Allowance for Credit Losses	10,996	17,595	13,124	13,053
Commercial real estate loans | Office, retail, and industrial | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	14,575	12,446
Total Allowance for Credit Losses	1,663	1,447
Commercial real estate loans | Multi-family
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	621	398
Loans Collectively Evaluated for Impairment	660,771	601,429
Loans	675,463	614,052
Allowance for Credit Losses Individually Evaluated for Impairment	0	0
Allowance for Credit Losses Collectively Evaluated for Impairment	2,436	3,059
Total Allowance for Credit Losses	2,534	3,261	2,469	2,387
Commercial real estate loans | Multi-family | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	14,071	12,225
Total Allowance for Credit Losses	98	202
Commercial real estate loans | Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	0	34
Loans Collectively Evaluated for Impairment	530,977	447,058
Loans	539,820	451,540
Allowance for Credit Losses Individually Evaluated for Impairment	0	0
Allowance for Credit Losses Collectively Evaluated for Impairment	3,331	3,280
Total Allowance for Credit Losses	3,481	3,444	1,440	3,031
Commercial real estate loans | Construction | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	8,843	4,448
Total Allowance for Credit Losses	150	164
Commercial real estate loans | Other commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	1,468	1,286
Loans Collectively Evaluated for Impairment	1,291,723	965,900
Loans	1,358,515	979,528
Allowance for Credit Losses Individually Evaluated for Impairment	0	18
Allowance for Credit Losses Collectively Evaluated for Impairment	5,415	6,613
Total Allowance for Credit Losses	6,381	7,739	$ 6,109	$ 9,019
Commercial real estate loans | Other commercial real estate | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	65,324	12,342
Total Allowance for Credit Losses	966	1,108
Total corporate loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	51,617	42,650
Loans Collectively Evaluated for Impairment	8,347,286	6,756,948
Loans	8,514,418	6,844,241
Allowance for Credit Losses Individually Evaluated for Impairment	10,074	525
Allowance for Credit Losses Collectively Evaluated for Impairment	65,808	68,654
Total Allowance for Credit Losses	79,183	72,748
Total corporate loans | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	115,515	44,643
Total Allowance for Credit Losses	3,301	3,569
Consumer loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Individually Evaluated for Impairment	0	0
Loans Collectively Evaluated for Impairment	1,901,456	1,392,880
Loans	1,923,394	1,409,904
Allowance for Credit Losses Individually Evaluated for Impairment	0	0
Allowance for Credit Losses Collectively Evaluated for Impairment	15,533	12,210
Total Allowance for Credit Losses	16,546	13,335
Consumer loans | PCI
Financing Receivable, Allowance for Credit Losses [Line Items]
PCI	21,938	17,024
Total Allowance for Credit Losses	$ 1,013	$ 1,125

Past Due Loans, Allowance For76

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Impaired Loans Individually Evaluated by Class (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	$ 13,477	$ 29,314
Recorded Investment in Loans with a Specific Reserve	38,140	13,336
Unpaid Principal Balance	69,625	53,144
Specific Reserve	10,074	525
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	4,234	11,579
Recorded Investment in Loans with a Specific Reserve	34,484	13,066
Unpaid Principal Balance	53,192	29,514
Specific Reserve	10,074	507
Commercial, industrial, and agricultural | Agricultural
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	0	0
Recorded Investment in Loans with a Specific Reserve	0	0
Unpaid Principal Balance	0	0
Specific Reserve	0	0
Commercial real estate loans
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	9,243	17,735
Recorded Investment in Loans with a Specific Reserve	3,656	270
Unpaid Principal Balance	16,433	23,630
Specific Reserve	0	18
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	7,154	16,287
Recorded Investment in Loans with a Specific Reserve	3,656	0
Unpaid Principal Balance	14,246	21,057
Specific Reserve	0	0
Commercial real estate loans | Multi-family
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	621	398
Recorded Investment in Loans with a Specific Reserve	0	0
Unpaid Principal Balance	621	398
Specific Reserve	0	0
Commercial real estate loans | Construction
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	0	34
Recorded Investment in Loans with a Specific Reserve	0	0
Unpaid Principal Balance	0	34
Specific Reserve	0	0
Commercial real estate loans | Other commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment in Loans with No Specific Reserve	1,468	1,016
Recorded Investment in Loans with a Specific Reserve	0	270
Unpaid Principal Balance	1,566	2,141
Specific Reserve	$ 0	$ 18

Past Due Loans, Allowance For77

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Impaired Loans Individually Evaluated by Class (Continued) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		$ 49,404	$ 25,396	$ 26,366
Interest Income Recognized	[1]	1,690	492	390
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		33,956	9,178	8,940
Interest Income Recognized	[1]	1,059	104	163
Commercial, industrial, and agricultural | Agricultural
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		279	0	0
Interest Income Recognized	[1]	101	0	0
Commercial real estate loans
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		15,170	16,218	17,426
Interest Income Recognized	[1]	530	388	227
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		13,106	12,867	9,359
Interest Income Recognized	[1]	325	291	52
Commercial real estate loans | Multi-family
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		441	479	855
Interest Income Recognized	[1]	28	11	13
Commercial real estate loans | Construction
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		7	63	3,902
Interest Income Recognized	[1]	136	0	118
Commercial real estate loans | Other commercial real estate
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		1,615	2,809	3,310
Interest Income Recognized	[1]	$ 41	$ 86	$ 44
[1]	Recorded using the cash basis of accounting.

Past Due Loans, Allowance For78

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Credit Quality Indicators by Class, Excluding Covered Loans (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Accruing		$ 1,796	$ 2,291
Special mention and substandard loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Accruing		657	834
Commercial, industrial, and agricultural | Commercial and industrial
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		3,529,914	2,827,658
Accruing		264	281
Commercial, industrial, and agricultural | Commercial and industrial | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		3,388,133	2,638,833
Commercial, industrial, and agricultural | Commercial and industrial | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	70,863	92,340
Commercial, industrial, and agricultural | Commercial and industrial | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	30,338	66,547
Commercial, industrial, and agricultural | Commercial and industrial | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	40,580	29,938
Commercial, industrial, and agricultural | Agricultural
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		430,886	389,496
Accruing		0	0
Commercial, industrial, and agricultural | Agricultural | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		413,946	366,382
Commercial, industrial, and agricultural | Agricultural | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	10,989	17,039
Commercial, industrial, and agricultural | Agricultural | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	5,732	5,894
Commercial, industrial, and agricultural | Agricultural | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	219	181
Commercial real estate loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		4,553,618	3,627,087
Accruing		766	1,009
Commercial real estate loans | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		4,395,481	3,488,742
Commercial real estate loans | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	72,749	50,296
Commercial real estate loans | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	69,621	67,283
Commercial real estate loans | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	15,767	20,766
Commercial real estate loans | Office, retail, and industrial
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,979,820	1,581,967
Accruing		0	155
Commercial real estate loans | Office, retail, and industrial | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,903,737	1,491,170
Commercial real estate loans | Office, retail, and industrial | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	25,546	34,007
Commercial real estate loans | Office, retail, and industrial | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	38,977	39,513
Commercial real estate loans | Office, retail, and industrial | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	11,560	17,277
Commercial real estate loans | Multi-family
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		675,463	614,052
Accruing		574	586
Commercial real estate loans | Multi-family | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		665,496	607,342
Commercial real estate loans | Multi-family | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	7,395	4,370
Commercial real estate loans | Multi-family | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	2,195	2,029
Commercial real estate loans | Multi-family | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	377	311
Commercial real estate loans | Construction
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		539,820	451,540
Accruing		0	0
Commercial real estate loans | Construction | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		521,911	438,946
Commercial real estate loans | Construction | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	10,184	111
Commercial real estate loans | Construction | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	7,516	12,197
Commercial real estate loans | Construction | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	209	286
Commercial real estate loans | Other commercial real estate
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,358,515	979,528
Accruing		192	268
Commercial real estate loans | Other commercial real estate | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,304,337	951,284
Commercial real estate loans | Other commercial real estate | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	29,624	11,808
Commercial real estate loans | Other commercial real estate | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	20,933	13,544
Commercial real estate loans | Other commercial real estate | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	3,621	2,892
Total corporate loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		8,514,418	6,844,241
Accruing		1,030	1,290
Total corporate loans | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		8,197,560	6,493,957
Total corporate loans | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	154,601	159,675
Total corporate loans | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	105,691	139,724
Total corporate loans | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	$ 56,566	$ 50,885
[1]	Loans categorized as special mention exhibit potential weaknesses that require the close attention of management since these potential weaknesses may result in the deterioration of repayment prospects in the future.
[2]	Total special mention and substandard loans includes accruing TDRs of $657,000 as of December 31, 2017 and $834,000 as of December 31, 2016.
[3]	Loans categorized as substandard exhibit a well-defined weakness that may jeopardize the liquidation of the debt. These loans continue to accrue interest because they are well-secured and collection of principal and interest is expected within a reasonable time.
[4]	Loans categorized as non-accrual exhibit a well-defined weakness that may jeopardize the liquidation of the debt or result in a loss if the deficiencies are not corrected.

Past Due Loans, Allowance For79

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) (Details) - Consumer loans - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	$ 1,923,394	$ 1,409,904
Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	1,913,036	1,401,500
Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	10,358	8,404
Home equity
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	827,055	747,983
Home equity | Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	821,109	742,518
Home equity | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	5,946	5,465
1-4 family mortgages
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	774,357	423,922
1-4 family mortgages | Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	769,945	420,983
1-4 family mortgages | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	4,412	2,939
Installment
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	321,982	237,999
Installment | Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	321,982	237,999
Installment | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Credit Quality Indicators by Class	$ 0	$ 0

Past Due Loans, Allowance For80

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - TDRs By Class (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Accruing		$ 1,796	$ 2,291
Non-accrual	[1]	24,533	6,297
Total		26,329	8,588	$ 5,067
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Accruing		264	281
Non-accrual	[1]	18,959	150
Total		19,223	431
Commercial, industrial, and agricultural | Agricultural
Financing Receivable, Modifications [Line Items]
Accruing		0	0
Non-accrual	[1]	0	0
Total		0	0
Commercial real estate loans
Financing Receivable, Modifications [Line Items]
Accruing		766	1,009
Non-accrual	[1]	4,385	4,949
Total		5,151	5,958
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Modifications [Line Items]
Accruing		0	155
Non-accrual	[1]	4,236	4,733
Total		4,236	4,888
Commercial real estate loans | Multi-family
Financing Receivable, Modifications [Line Items]
Accruing		574	586
Non-accrual	[1]	149	168
Total		723	754
Commercial real estate loans | Construction
Financing Receivable, Modifications [Line Items]
Accruing		0	0
Non-accrual	[1]	0	0
Total		0	0
Commercial real estate loans | Other commercial real estate
Financing Receivable, Modifications [Line Items]
Accruing		192	268
Non-accrual	[1]	0	48
Total		192	316
Total corporate loans
Financing Receivable, Modifications [Line Items]
Accruing		1,030	1,290
Non-accrual	[1]	23,344	5,099
Total		24,374	6,389
Consumer loans
Financing Receivable, Modifications [Line Items]
Accruing		766	1,001
Non-accrual	[1]	1,189	1,198
Total		1,955	2,199
Consumer loans | Home equity
Financing Receivable, Modifications [Line Items]
Accruing		86	177
Non-accrual	[1]	738	820
Total		824	997
Consumer loans | 1-4 family mortgages
Financing Receivable, Modifications [Line Items]
Accruing		680	824
Non-accrual	[1]	451	378
Total		1,131	1,202
Consumer loans | Installment
Financing Receivable, Modifications [Line Items]
Accruing		0	0
Non-accrual	[1]	0	0
Total		$ 0	$ 0
[1]	These TDRs are included in non-accrual loans in the preceding tables.

Past Due Loans, Allowance For81

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Narrative (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Valuation allowance on TDR loans	$ 2,000,000	$ 0
Commitments to lend additional funds on TDR loans	$ 0	$ 0

Past Due Loans, Allowance For82

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - TDRs That Were Restructured (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	14	2	3
Pre-Modification Recorded Investment	$ 30,389	$ 6,205	$ 445
Funds Disbursed	9,035	0	0
Interest and Escrow Capitalized	0	0	0
Charge-offs	6,232	1,083	0
Post-Modification Recorded Investment	$ 33,192	$ 5,122	$ 445
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	12
Pre-Modification Recorded Investment	$ 26,733
Funds Disbursed	9,035
Interest and Escrow Capitalized	0
Charge-offs	6,232
Post-Modification Recorded Investment	$ 29,536
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2	1
Pre-Modification Recorded Investment	$ 3,656	$ 5,460
Funds Disbursed	0	0
Interest and Escrow Capitalized	0	0
Charge-offs	0	1,083
Post-Modification Recorded Investment	$ 3,656	$ 4,377
Commercial real estate loans | Other commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Loans | loan		1
Pre-Modification Recorded Investment		$ 745
Funds Disbursed		0
Interest and Escrow Capitalized		0
Charge-offs		0
Post-Modification Recorded Investment		$ 745
Consumer loans | Home equity
Financing Receivable, Modifications [Line Items]
Number of Loans | loan			1
Pre-Modification Recorded Investment			$ 120
Funds Disbursed			0
Interest and Escrow Capitalized			0
Charge-offs			0
Post-Modification Recorded Investment			$ 120
Consumer loans | 1-4 family mortgages
Financing Receivable, Modifications [Line Items]
Number of Loans | loan			2
Pre-Modification Recorded Investment			$ 325
Funds Disbursed			0
Interest and Escrow Capitalized			0
Charge-offs			0
Post-Modification Recorded Investment			$ 325

Past Due Loans, Allowance For83

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - TDRs That Defaulted Within Twelve Months of the Restructured Date (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	1	0
Recorded Investment | $	$ 0	$ 119	$ 0
Consumer loans | Home equity
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	1	0
Recorded Investment | $	$ 0	$ 119	$ 0

Past Due Loans, Allowance For84

Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - TDR Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	$ 8,588	$ 5,067
Additions	33,192	5,122	$ 445
Ending balance	26,329	8,588	5,067
Accruing
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	2,291	2,743	3,704
Additions	15,819	0	120
Net payments	(1,923)	(120)	(774)
Returned to performing status	0	0	0
Net transfers to non-accrual	(14,391)	(332)	(307)
Ending balance	1,796	2,291	2,743
Non-accrual
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	6,297	2,324	19,904
Additions	14,570	6,205	325
Net payments	(4,380)	(1,072)	(15,525)
Charge-offs	(6,345)	(1,492)	(2,687)
Transfers to OREO	0	0	0
Loans sold	0	0	0
Net transfers from accruing	14,391	332	307
Ending balance	$ 24,533	$ 6,297	$ 2,324

Premises, Furniture, and Equi85

Premises, Furniture, and Equipment - Premises, Furniture, and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 30,470	$ 18,304
Premises	123,873	94,369
Furniture and equipment	115,013	105,859
Total cost	269,356	218,532
Accumulated depreciation	(148,248)	(140,030)
Net book value of premises, furniture, and equipment	121,108	78,502
Assets held-for-sale	2,208	4,075
Premises, furniture, and equipment, net	$ 123,316	$ 82,577

Premises, Furniture, and Equi86

Premises, Furniture, and Equipment - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)renewal_optionretail_branch	Dec. 31, 2015USD ($)	Sep. 27, 2016USD ($)
Property, Plant and Equipment [Line Items]
Aggregate cash purchase price		$ 150,300
Number of branches sold | retail_branch		55
Net book value of properties		$ 58,800
Renewal term of lease for sale-leaseback transaction		14 years
Number of lease renewal options | renewal_option		5
Pre-tax gain on sale-leaseback transaction		$ 88,000
Net gain on sale-leaseback transaction	$ 0	5,509	$ 0
Deferred gain, net	74,600	81,000		$ 82,500
Depreciation of premises, furniture, and equipment	$ 13,995	$ 12,804	$ 13,367
Five Year Renewal Period
Property, Plant and Equipment [Line Items]
Renewal term of lease for sale-leaseback transaction		5 years

Premises, Furniture, and Equi87

Premises, Furniture, and Equipment - Future Minimum Operating Lease Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Property, Plant and Equipment [Abstract]
2,018	$ 19,241
2,019	17,659
2,020	16,926
2,021	16,732
2,022	16,464
2023 and thereafter	119,847
Total minimum lease payments	$ 206,869

Premises, Furniture, and Equi88

Premises, Furniture, and Equipment - Accretion of Operating Leases (Details) $ in Thousands	Dec. 31, 2017USD ($)
Property, Plant and Equipment [Abstract]
2,018	$ 935
2,019	685
2,020	648
2,021	648
2,022	639
2023 and thereafter	3,358
Total accretion	$ 6,913

Premises, Furniture, and Equi89

Premises, Furniture, and Equipment - Rental Expense (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Lease expense charged to operations		$ 18,666	$ 11,207	$ 6,850
Accretion of operating lease intangible	[1]	(1,180)	(1,171)	(1,144)
Accretion of deferred gain on sale-leaseback transaction	[1]	(5,872)	(1,473)	0
Rental income from premises leased to others	[1]	(682)	(527)	(606)
Net operating lease expense		$ 10,932	$ 8,036	$ 5,100
[1]	Included as reductions to net occupancy and equipment expense in the Consolidated Statements of Income.

Goodwill and Other Intangible90

Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Beginning balance	$ 340,879	$ 319,007	$ 310,589
Acquisitions	356,729	21,872	8,418
Ending balance	$ 697,608	$ 340,879	$ 319,007

Goodwill and Other Intangible91

Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-lived Intangible Assets [Roll Forward]
Balance at the beginning of the year, gross	$ 58,959	$ 48,550	$ 47,970
Balance at the beginning of the year, accumulated amortization	32,962	28,280	24,360
Balance at the beginning of the year, net	25,997	20,270	23,610
Additions	39,017	10,409	580
Amortization expense	(7,865)	(4,682)	(3,920)
Balance at the end of the year, gross	97,976	58,959	48,550
Balance at the end of the year, accumulated amortization	40,827	32,962	28,280
Balance at the end of the year, net	$ 57,149	$ 25,997	$ 20,270
Weighted-average remaining life (in years)	8 years 4 months	7 years 6 months 20 days	7 years 5 months 9 days
Minimum
Finite-lived Intangible Assets [Roll Forward]
Estimated useful lives (in years)	2 months	7 months	9 months 6 days
Maximum
Finite-lived Intangible Assets [Roll Forward]
Estimated useful lives (in years)	9 years 3 months	9 years 3 months	10 years

Goodwill and Other Intangible92

Goodwill and Other Intangible Assets - Amortization of Other Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
2,018	$ 7,139
2,019	7,073
2,020	7,023
2,021	6,946
2,022	6,867
2023 and thereafter	22,101
Total	$ 57,149	$ 25,997	$ 20,270	$ 23,610

Deposits - Summary of Deposits

Deposits - Summary of Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Demand deposits	$ 3,576,190	$ 2,766,748
Savings deposits	2,011,999	1,615,833
NOW accounts	1,962,304	1,675,421
Money market deposits	1,856,049	1,577,316
Time deposits less than $100,000	904,882	755,558
Time deposits greater than $100,000	741,901	437,727
Total deposits	$ 11,053,325	$ 8,828,603

Deposits - Maturities of Time

Deposits - Maturities of Time Deposits (Details) $ in Thousands	Dec. 31, 2017USD ($)
Maturities of Time Deposits [Abstract]
2,018	$ 1,086,528
2,019	418,176
2,020	86,196
2,021	38,569
2,022	16,845
2023 and thereafter	469
Total	$ 1,646,783

Borrowed Funds - Summary of Bo

Borrowed Funds - Summary of Borrowed Funds (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Securities sold under agreements to repurchase	$ 124,884	$ 129,008
FHLB advances	590,000	750,000
Total borrowed funds	$ 714,884	$ 879,008

Borrowed Funds - Narrative (De

Borrowed Funds - Narrative (Details) - USD ($)	Sep. 27, 2016	Dec. 31, 2017
Short-term Debt [Line Items]
Line of credit maximum borrowing capacity	$ 50,000,000
Line of credit unused facility fee	0.35%
Line of credit amount outstanding		$ 0
One-Month LIBOR Plus 1.75%
Short-term Debt [Line Items]
Line of credit interest rate spread	1.75%
FHLB Advances
Short-term Debt [Line Items]
FHLB maturity date range, start		Jan. 2, 2018
FHLB maturity date range, end		Mar. 1, 2018
FHLB Advances | Minimum
Short-term Debt [Line Items]
FHLB fixed interest rate		1.30%
FHLB Advances | Maximum
Short-term Debt [Line Items]
FHLB fixed interest rate		1.46%

Borrowed Funds - Short-Term Cr

Borrowed Funds - Short-Term Credit Lines Available for Use (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
FRBs Discount Window Primary Credit Program
Line of Credit Facility [Line Items]
Amount outstanding	$ 843,618	$ 629,699
Available federal funds lines
Line of Credit Facility [Line Items]
Amount outstanding	667,000	632,000
Correspondent bank line of credit
Line of Credit Facility [Line Items]
Amount outstanding	$ 50,000	$ 50,000

Senior and Subordinated Debt (D

Senior and Subordinated Debt (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Sep. 29, 2016
Debt Instrument [Line Items]
Total junior subordinated debentures		$ 48,243	$ 48,030
Senior and subordinated debt		195,170	194,603
Great Lakes Statutory Trust II (GLST II)
Debt Instrument [Line Items]
Debt instrument, unamortized discount		1,700	1,800
Great Lakes Statutory Trust III (GLST III)
Debt Instrument [Line Items]
Debt instrument, unamortized discount		2,300	2,400
Subordinated notes due in 2026
Debt Instrument [Line Items]
Subordinated notes		$ 146,927	$ 146,573	$ 150,000
Issuance date		Sep. 29, 2016
Maturity date		Sep. 29, 2026
Interest rate		5.875%	5.875%	5.875%
Junior Subordinated Debentures, First Midwest Capital Trust I | First Midwest Capital Trust I (FMCT)
Debt Instrument [Line Items]
Total junior subordinated debentures		$ 37,801	$ 37,800
Issuance date		Nov. 11, 2003
Maturity date		Dec. 1, 2033
Interest rate		6.95%	6.95%
Junior Subordinated Debentures, Great Lakes Statutory Trust II | Great Lakes Statutory Trust II (GLST II)
Debt Instrument [Line Items]
Total junior subordinated debentures	[1]	$ 4,486	$ 4,391
Issuance date	[1]	Dec. 15, 2005
Maturity date	[1]	Dec. 15, 2035
Basis spread on variable interest rate	[1],[2]	1.40%	1.40%
Junior Subordinated Debentures, Great Lakes Statutory Trust III | Great Lakes Statutory Trust III (GLST III)
Debt Instrument [Line Items]
Total junior subordinated debentures	[1]	$ 5,956	$ 5,839
Issuance date	[1]	Jun. 15, 2007
Maturity date	[1]	Sep. 15, 2037
Basis spread on variable interest rate	[1],[2]	1.70%	1.70%
[1]	The junior subordinated debentures related to GLST II and GLST III were assumed by the Company through an acquisition. As of December 31, 2017, these amounts include acquisition adjustments which resulted in a discount of $1.7 million to GLST II and $2.3 million to GLST III. The acquisition adjustments totaled $1.8 million and $2.4 million to GLST II and GLST III, respectively, as of December 31, 2016.
[2]	The interest rates are a variable rate based on the three-month LIBOR plus 1.400% and 1.700% for GLST II and GLST III, respectively.

Senior and Subordinated Debt -

Senior and Subordinated Debt - Narrative (Details) - USD ($) $ in Thousands	Sep. 29, 2016	Dec. 31, 2017	Dec. 31, 2016	Nov. 22, 2016	Apr. 01, 2016
Subordinated notes due in 2016
Debt Instrument [Line Items]
Subordinated notes					$ 38,500
Interest rate					5.85%
Subordinated notes due in 2026
Debt Instrument [Line Items]
Subordinated notes	$ 150,000	$ 146,927	$ 146,573
Interest rate	5.875%	5.875%	5.875%
Proceeds from issuance of debt	$ 146,500
Senior notes
Debt Instrument [Line Items]
Interest rate				5.875%
Senior notes				$ 115,000

Material Transactions Affect100

Material Transactions Affecting Stockholders' Equity (Details) - $ / shares	May 17, 2017	Jan. 06, 2017	Mar. 08, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Class of Stock [Line Items]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01	$ 0.01				$ 0.01
Common stock, increase shares authorized (in shares)	100,000,000
Common stock and preferred stock, shares authorized (in shares)	251,000,000
Preferred stock, shares authorized (in shares)	1,000,000			1,000,000				1,000,000
Common stock, shares authorized (in shares)	250,000,000			250,000,000				150,000,000
Common dividends declared per common share (in dollars per share)				$ 0.10	$ 0.10	$ 0.10	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09
Standard Bancshares, Inc.
Class of Stock [Line Items]
Common stock, shares issued (in shares)		21,057,085
Shares issued (in dollars per share)		$ 25.34
NI Bancshares Corporation
Class of Stock [Line Items]
Common stock, shares issued (in shares)			3,042,494
Shares issued (in dollars per share)			$ 18.059
Standard Bancshares, Inc.
Class of Stock [Line Items]
Shares issued (in dollars per share)		$ 25.34

Earnings Per Common Share - Bas

Earnings Per Common Share - Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income		$ 98,387	$ 92,349	$ 82,064
Net income applicable to non-vested restricted shares		(916)	(1,043)	(882)
Net income applicable to common shares		$ 97,471	$ 91,306	$ 81,182
Weighted-average common shares outstanding:
Weighted-average common shares outstanding (basic) (in shares)		101,423	79,797	77,059
Dilutive effect of common stock equivalents (in shares)		20	13	13
Weighted-average diluted common shares outstanding (in shares)		101,443	79,810	77,072
Basic EPS (in dollars per share)		$ 0.96	$ 1.14	$ 1.05
Diluted EPS (in dollars per share)		$ 0.96	$ 1.14	$ 1.05
Anti-dilutive shares not included in the computation of diluted EPS (in shares)	[1]	229	494	800
[1]	This amount represents outstanding stock options for which the exercise price is greater than the average market price of the Company's common stock.

Income Taxes - Components of I

Income Taxes - Components of Income Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax expense:
Federal	$ 93,540	$ 46,748	$ 18,524
State	104	790	2,326
Total	93,644	47,538	20,850
Deferred income tax (benefit) expense:
Federal	(12,219)	(7,786)	12,048
State	8,142	6,419	4,849
Total	(4,077)	(1,367)	16,897
Total income tax expense	$ 89,567	$ 46,171	$ 37,747

Income Taxes - Narrative (Deta

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Acquired thrift's tax bad debt reserve	$ 2,500		$ 2,500	$ 2,500	$ 2,500
Deferred tax assets, net	64,736		64,736	100,207
Unrecognized tax benefit that would affect effective tax rate	12,900		12,900	1,400	$ 936,000
Standard Bancshares and NI Bancshares Acquisitions
Income Taxes [Line Items]
Deferred tax assets, net	41,500		41,500
NI Bancshares and Peoples Bank Acquisitions
Income Taxes [Line Items]
Deferred tax assets, net				$ 4,400
Federal
Income Taxes [Line Items]
Revaluation of deferred tax assets	$ (26,600)		(26,600)
State and Local Jurisdiction
Income Taxes [Line Items]
Revaluation of deferred tax assets		$ 2,800	$ 2,800

Income Taxes - Components of E

Income Taxes - Components of Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory federal income tax	$ 65,784	$ 48,482	$ 41,934
Statutory federal income tax rate (percent of pretax income)	35.00%	35.00%	35.00%
Revaluation of deferred tax assets	$ 23,709	$ 0	$ 0
Revaluation of deferred tax assets (percent of pretax income)	12.60%	0.00%	0.00%
Tax-exempt income, net of interest expense disallowance	$ (5,065)	$ (5,439)	$ (6,752)
Tax-exempt income, net of interest expense disallowance (percent of pretax income)	(2.70%)	(3.90%)	(5.60%)
State income tax, net of federal income tax effect	$ 5,069	$ 4,323	$ 4,665
State income tax, net of federal income tax effect (percent of pretax income)	2.70%	3.10%	3.90%
Other	$ 70	$ (1,195)	$ (2,100)
Other (percent of pretax income)	0.10%	(0.90%)	(1.80%)
Total income tax expense	$ 89,567	$ 46,171	$ 37,747
Effective tax rate	47.70%	33.30%	31.50%

Income Taxes - Deferred Tax As

Income Taxes - Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowance for credit losses	$ 20,285	$ 30,399
Deferred gain on sale-leaseback transaction	15,668	28,133
Equity based compensation	3,605	5,228
Federal and state net operating loss (NOL) carryforwards	3,384	388
Acquisition adjustments	2,489	0
OREO	2,089	4,336
Non-equity based compensation	897	6,060
AMT and other credit carryforwards	667	90
Unrealized losses on securities	23	18,320
Other	12,494	10,997
Total deferred tax assets	61,601	103,951
Deferred tax liabilities:
Deferred loan fees and costs	(4,169)	(3,172)
Accrued retirement benefits	(3,517)	(6,281)
Fixed assets	(1,660)	(397)
Cancellation of indebtedness income	(641)	(2,136)
Acquisition adjustments	0	(13,407)
Other	(2,449)	(6,045)
Total deferred tax liabilities	(12,436)	(31,438)
Deferred tax valuation allowance	0	0
Net deferred tax assets	49,165	72,513
Tax effect of adjustments related to other comprehensive income (loss)	15,571	27,694
Net deferred tax assets including adjustments	64,736	100,207
NOL carryforwards available to offset future taxable income:
AMT credits	410	0
Internal Revenue Service (IRS)
NOL carryforwards available to offset future taxable income:
Gross NOL Carryforwards	0	574
Illinois
NOL carryforwards available to offset future taxable income:
Gross NOL Carryforwards	188,995	26,342
Indiana
NOL carryforwards available to offset future taxable income:
Gross NOL Carryforwards	$ 16,174	$ 1,003

Income Taxes - Rollforward of

Income Taxes - Rollforward of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance		$ 2,039	$ 1,408	$ 912
Additions for tax positions relating to the current year		845	640	480
Additions for tax positions relating to prior years		13,389	0	37
Reductions for tax positions relating to prior years		(25)	(9)	(21)
Ending balance		16,248	2,039	1,408
Interest and penalties not included above:
Interest expense, net of tax effect, and penalties	[1]	118	49	20
Accrued interest and penalties, net of tax effect, at end of year	[1]	$ 191	$ 73	$ 24
[1]	Included in income tax expense in the Consolidated Statements of Income.

Employee Benefit Plans - Narra

Employee Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined contribution plan, employer matching contribution percent of employee's compensation			4.00%	2.00%
Defined contribution plan, transition contribution in next fiscal year (up to) (percent)		4.00%
Defined contribution plan, discretionary contribution vesting period	6 years
Actuarial losses as a percentage of accumulated benefit obligation	37.50%				41.30%
Pension Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Actuarial losses as a percentage of accumulated benefit obligation	10.00%
Contributions
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined contribution plan, employee contribution limit, percentage of compensation			100.00%	45.00%
Certain Highly Compensated Employees
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined contribution plan, employee contribution limit, percentage of compensation				15.00%
Voluntary 401K Plans
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined contribution plan, employer automatic contribution limit	2.00%
Deferred Profit Sharing
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined contribution plan, employer automatic contribution limit	15.00%

Employee Benefit Plans - Profi

Employee Benefit Plans - Profit Sharing Plan (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plan Disclosure [Line Items]
Profit sharing expense		$ 41,886	$ 33,309	$ 31,852
Profit Sharing Expense
Defined Contribution Plan Disclosure [Line Items]
Profit sharing expense	[1]	7,346	6,171	6,919
Company dividends received by the Profit Sharing Plan		$ 441	$ 494	$ 466
Company shares held by the Profit Sharing Plan at the end of the year:
Number of shares		1,079,975	1,175,858	1,277,567
Fair value		$ 25,930	$ 29,667	$ 23,546
[1]	Included in retirement and other employee benefits in the Consolidated Statements of Income.

Employee Benefit Plans - Pensi

Employee Benefit Plans - Pension Plan Cost and Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Accumulated benefit obligation	$ 67,923		$ 68,959
Change in projected benefit obligation
Beginning balance	68,959		67,185
Service cost	0		0
Interest cost	1,712		1,635	$ 2,334
Settlements	(6,271)		(3,136)
Actuarial loss	4,240		3,851
Benefits paid	(717)		(576)
Ending balance	67,923		68,959	67,185
Change in fair value of plan assets
Beginning balance	65,189		64,903
Actual return on plan assets	7,958		3,998
Benefits paid	(717)		(576)
Settlements	(6,271)		(3,136)
Ending balance	66,159	[1]	65,189	$ 64,903
Funded status recognized in the Consolidated Statements of Financial Condition
Noncurrent liability	(1,764)		(3,770)
Amounts recognized in accumulated other comprehensive loss
Prior service cost	0		0
Net loss	25,495		28,483
Net amount recognized	$ 25,495		$ 28,483
Actuarial losses included in accumulated other comprehensive loss as a percent of
Accumulated benefit obligation	37.50%		41.30%
Fair value of plan assets	38.50%		43.70%
Amounts expected to be amortized from accumulated other comprehensive loss into net periodic benefit cost in the next fiscal year
Prior service cost	$ 0		$ 0
Net loss	561		582
Net amount expected to be recognized	$ 561		$ 582
Weighted-average assumptions at the end of the year used to determine the actuarial present value of the projected benefit obligation
Discount rate	3.45%		3.86%
[1]	Additional information regarding the fair value of Pension Plan assets as of December 31, 2017 can be found in Note 21, "Fair Value."

Employee Benefit Plans - Net P

Employee Benefit Plans - Net Periodic Benefit Pension Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of net periodic benefit cost
Interest cost	$ 1,712	$ 1,635	$ 2,334
Expected return on plan assets	(3,802)	(4,057)	(4,333)
Recognized net actuarial loss	591	571	367
Amortization of prior service cost	0	0	0
Recognized settlement loss	2,480	1,338	2,254
Net periodic cost (income)	981	(513)	622
Other changes in plan assets and benefit obligations recognized as a charge to other comprehensive income (loss)
Net loss for the period	(83)	(3,911)	(9,191)
Amortization of net loss	3,071	1,909	2,621
Total unrealized gain (loss)	2,988	(2,002)	(6,570)
Total recognized in net periodic pension cost and other comprehensive income (loss)	$ 2,007	$ (1,489)	$ (7,192)
Weighted-average assumptions used to determine the net periodic cost
Discount rate	3.86%	3.99%	3.60%
Expected return on plan assets	6.25%	6.50%	6.50%

Employee Benefit Plans - Pe111

Employee Benefit Plans - Pension Plan Asset Allocation (Details) - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Asset Category
Fair Value of Plan Assets (in dollars)		$ 66,159	[1]	$ 65,189	$ 64,903
Percentage of Plan Assets		100.00%		100.00%
Equity securities
Asset Category
Fair Value of Plan Assets (in dollars)	[1]	$ 39,954
Percentage of Plan Assets		60.00%		60.00%
Fixed income
Asset Category
Fair Value of Plan Assets (in dollars)	[1]	$ 22,734
Percentage of Plan Assets		35.00%		33.00%
Cash equivalents
Asset Category
Fair Value of Plan Assets (in dollars)	[1]	$ 3,471
Percentage of Plan Assets		5.00%		7.00%
Minimum | Equity securities
Asset Category
Target plan asset allocations		50.00%
Minimum | Fixed income
Asset Category
Target plan asset allocations		30.00%
Minimum | Cash equivalents
Asset Category
Target plan asset allocations		2.00%
Maximum | Equity securities
Asset Category
Target plan asset allocations		60.00%
Maximum | Fixed income
Asset Category
Target plan asset allocations		48.00%
Maximum | Cash equivalents
Asset Category
Target plan asset allocations		10.00%
[1]	Additional information regarding the fair value of Pension Plan assets as of December 31, 2017 can be found in Note 21, "Fair Value."

Employee Benefit Plans - Estim

Employee Benefit Plans - Estimated Future Pension Benefit Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Retirement Benefits [Abstract]
2,018	$ 6,849
2,019	5,462
2,020	5,366
2,021	5,216
2,022	5,064
2023-2026	$ 20,222

Share-Based Compensation - Nar

Share-Based Compensation - Narrative (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award term	10 years
Granted (in shares)	16,000	18,000
Directors Plan | Accelerated Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Nonqualified Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award term	10 years
Stock options granted in period (in shares)	0	0	0
Stock options exercised in period (in shares)	0	0	0
Restricted Stock And Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Granted (in shares)	477,000
Restricted Stock And Restricted Stock Unit Awards | Vesting After Two Years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights percentage	50.00%
Restricted Stock And Restricted Stock Unit Awards | Vesting After Three Years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights percentage	50.00%
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of internal and external performance metric analysis	3 years
Metric weighting (percent)	50.00%
Granted (in shares)	145,000
Performance Shares | Vesting After Three Years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights percentage	33.33%
Performance Shares | Vesting After Fourth Years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights percentage	33.33%
Performance Shares | Vesting After Fifth Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights percentage	33.33%
Performance Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares earned of those granted based on performance	0.00%
Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares earned of those granted based on performance	200.00%

Share-Based Compensation - Sha

Share-Based Compensation - Shares of Common Stock Available Under Share-Based Plans (Details)	Dec. 31, 2017shares
Omnibus Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Authorized (in shares)	8,631,641
Shares Available For Grant (in shares)	1,835,929
Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Authorized (in shares)	481,250
Shares Available For Grant (in shares)	104,782

Share-Based Compensation - Non

Share-Based Compensation - Nonqualified Stock Option Transactions (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Number of Options
Options outstanding beginning balance (in shares) | shares	486
Expired (in shares) | shares	(254)
Options outstanding ending balance (in shares) | shares	232
Exercisable at the end of the year (in shares) | shares	232
Weighted Average Exercise Price
Options outstanding beginning balance (in dollars per share) | $ / shares	$ 31.77
Expired (in dollars per share) | $ / shares	37.78
Options outstanding ending balance (in dollars per share) | $ / shares	25.19
Exercisable at the end of the year (in dollars per share) | $ / shares	$ 25.19
Weighted average remaining contractual term of options outstanding ending balance (in years)	9 months	[1]
Weighted average remaining contractual term of options exercisable at the end of the year (in years)	9 months	[1]
Aggregate intrinsic value of options outstanding at the end of the year | $	$ 513	[2]
Aggregate intrinsic value of options exercisable at the end of the year | $	$ 513	[2]
[1]	Represents the average remaining contractual life in years.
[2]	Aggregate intrinsic value represents the total pre-tax intrinsic value that would have been received by the option holders if they had exercised their options on December 31, 2017. Intrinsic value equals the difference between the Company's average of the high and low stock price on the last trading day of the year and the option exercise price, multiplied by the number of shares. This amount will fluctuate with changes in the fair value of the Company's common stock.

Share-Based Compensation - Res

Share-Based Compensation - Restricted Stock Award Transactions (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Restricted Stock/Unit Awards
Number of Shares/Units
Non-vested awards at beginning of year (in shares) | shares	989
Granted (in shares) | shares	477
Vested (in shares) | shares	(367)
Forfeited (in shares) | shares	(46)
Non-vested awards at end of year (in shares) | shares	1,053
Weighted Average Grant Date Fair Value
Non-vested awards at beginning of year (in dollars per share) | $ / shares	$ 16.95
Granted (in dollars per share) | $ / shares	24.71
Vested (in dollars per share) | $ / shares	16.79
Forfeited (in dollars per share) | $ / shares	19.80
Non-vested awards at end of year (in dollars per share) | $ / shares	$ 20.36
Performance Shares
Number of Shares/Units
Non-vested awards at beginning of year (in shares) | shares	408
Granted (in shares) | shares	145
Vested (in shares) | shares	(54)
Forfeited (in shares) | shares	(33)
Non-vested awards at end of year (in shares) | shares	466
Weighted Average Grant Date Fair Value
Non-vested awards at beginning of year (in dollars per share) | $ / shares	$ 15.78
Granted (in dollars per share) | $ / shares	24.71
Vested (in dollars per share) | $ / shares	16.79
Forfeited (in dollars per share) | $ / shares	19.80
Non-vested awards at end of year (in dollars per share) | $ / shares	$ 18.16

Share-Based Compensation - Oth

Share-Based Compensation - Other Restricted Stock Award/Unit Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefit realized from the vesting/release of restricted stock, restricted stock unit, and performance share awards	$ 4,601	$ 3,152	$ 2,962
Restricted Stock Restricted Stock Unit and Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of restricted stock, restricted stock unit, and performance share awards granted during the year (in dollars per share)	$ 24.71	$ 17.28	$ 16.95
Total fair value of restricted stock, restricted stock unit, and performance share awards vested during the year	$ 13,760	$ 12,231	$ 7,615
Income tax benefit realized from the vesting/release of restricted stock, restricted stock unit, and performance share awards	$ 4,007	$ 2,529	$ 2,368

Share-Based Compensation - Eff

Share-Based Compensation - Effect of Recording Share-Based Compensation Expense (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based compensation expense	[1]	$ 11,223	$ 7,879	$ 7,242
Income tax benefit		4,601	3,152	2,962
Share-based compensation expense, net of tax		6,622	4,727	4,280
Unrecognized compensation expense		$ 13,266	$ 9,990	$ 8,644
Weighted-average amortization period remaining (in years)		1 year 3 months 10 days	1 year 4 months	1 year 4 months 7 days
[1]	Comprised of restricted stock, restricted stock unit, and performance share awards expense.

Regulatory and Capital Matte119

Regulatory and Capital Matters - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash reserve balance	$ 121,000,000	$ 85,400,000
Adjustment to available dividends	107,800,000
Regulatory capital requirements under banking regulations, inclusion of trust-preferred securities in Tier One capital calculation (less than)	15,000,000,000
Trust-preferred securities included in Tier 1 capital	$ 50,700,000
Tier 1 risk based capital conservation buffer initial requirements phasing duration	4 years
Implementation of deductions and other adjustments to CET1, percentage			40.00%
Implementation of deductions and other adjustments to CET1 additional, percentage	20.00%
Risk weighted threshold of items deducted from CET1 capital	10.00%
Aggregate risk weighted threshold of items deducted from CET1	15.00%
Minimum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk-weighting	0.00%
Maximum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk-weighting	600.00%
January 2,019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Minimum ratio of CET1 to risk-weighted assets	4.50%
Capital conservation buffer	2.50%
Resulting minimum ratio of CET1 to risk-weighted assets after capital conversion buffer	7.00%
Minimum ratio of Tier 1 capital to risk-weighted assets	6.00%
Minimum ratio of Tier 1 capital to risk-weighted assets, adjusted	8.50%
Minimum ratio of Total capital to risk-weighted assets	8.00%
Minimum ratio of Total capital to risk-weighted assets, adjusted	10.50%
Minimum leverage ratio	4.00%

Regulatory and Capital Matte120

Regulatory and Capital Matters - Summary of Capital Ratios (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
First Midwest Bancorp, Inc.
Total capital to risk-weighted assets:
Actual Capital	$ 1,448,124	$ 1,225,529
Actual Ratio (percent)	12.15%	12.23%
Adequately Capitalized Capital	$ 1,102,634	$ 864,176
Adequately Capitalized Ratio (percent)	9.25%	8.625%
Tier 1 capital to risk-weighted assets:
Actual Capital	$ 1,204,468	$ 991,873
Actual Ratio (percent)	10.10%	9.90%
Adequately Capitalized Capital	$ 864,227	$ 663,788
Adequately Capitalized Ratio (percent)	7.25%	6.625%
CET1 to risk-weighted assets:
Actual Capital	$ 1,153,939	$ 941,315
Actual Ratio (percent)	9.68%	9.39%
Adequately Capitalized Capital	$ 685,421	$ 513,496
Adequately Capitalized Ratio (percent)	5.75%	5.125%
Tier 1 capital to average assets:
Actual Capital	$ 1,204,468	$ 991,873
Actual Ratio (percent)	8.99%	8.99%
Adequately Capitalized Capital	$ 536,200	$ 441,473
Adequately Capitalized Ratio (percent)	4.00%	4.00%
First Midwest Bank
Total capital to risk-weighted assets:
Actual Capital	$ 1,300,809	$ 1,043,482
Actual Ratio (percent)	10.95%	10.73%
Adequately Capitalized Capital	$ 1,099,133	$ 838,741
Adequately Capitalized Ratio (percent)	9.25%	8.625%
To Be Well-Capitalized Under Prompt Corrective Action Provisions Capital	$ 1,188,252	$ 972,454
To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	10.00%	10.00%
Tier 1 capital to risk-weighted assets:
Actual Capital	$ 1,204,080	$ 956,399
Actual Ratio (percent)	10.13%	9.83%
Adequately Capitalized Capital	$ 861,482	$ 644,251
Adequately Capitalized Ratio (percent)	7.25%	6.625%
To Be Well-Capitalized Under Prompt Corrective Action Provisions Capital	$ 950,601	$ 777,963
To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	8.00%	8.00%
CET1 to risk-weighted assets:
Actual Capital	$ 1,204,080	$ 956,399
Actual Ratio (percent)	10.13%	9.83%
Adequately Capitalized Capital	$ 683,245	$ 498,383
Adequately Capitalized Ratio (percent)	5.75%	5.125%
To be Well-Capitalized Under Prompt Corrective Action Provisions Capital	$ 772,364	$ 632,095
To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio ( percent)	6.50%	6.50%
Tier 1 capital to average assets:
Actual Capital	$ 1,204,080	$ 956,399
Actual Ratio (percent)	9.10%	8.76%
Adequately Capitalized Capital	$ 529,147	$ 436,560
Adequately Capitalized Ratio (percent)	4.00%	4.00%
To Be Well-Capitalized Under Prompt Corrective Action Provisions Capital	$ 661,434	$ 545,700
To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	5.00%	5.00%

Derivative Instruments and H121

Derivative Instruments and Hedging Activities - Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross notional amount outstanding		$ 5,458	$ 5,958
Derivative liability fair value		$ (101)	$ (282)
Weighted-average interest rate received		3.38%	2.63%
Weighted-average interest rate paid		5.96%	5.96%
Weighted-average maturity (in years)		10 months 4 days	1 year 10 months 1 day
Fair value of derivative	[1]	$ 110	$ 296
[1]	This amount represents the fair value if credit risk related contingent features were triggered.

Derivative Instruments and H122

Derivative Instruments and Hedging Activities - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value hedge ineffectiveness	$ 0	$ 0	$ 0
Amount hedged of borrowed funds using forward starting interest rate swaps				$ 415,000
Amount to be hedged of borrowed funds using forward staring interest rate swaps	$ 565,000
Weighted-average interest rate to be paid	1.96%
Cash flow ineffectiveness	$ 0	0	0
Interest rate cash flow hedge to be reclassified during next 12 months, net	1,600
Capital market products income	$ 8,171	$ 10,024	$ 4,806
Portion of fair value outstanding, interest rate swaps covered by collateral agreements (percent)	100.00%	100.00%
Cash Flow Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of variable rate loans hedged using interest rate swaps	$ 980,000
Amount hedged of borrowed funds using forward starting interest rate swaps	$ 980,000

Derivative Instruments and H123

Derivative Instruments and Hedging Activities - Cash Flow Hedges (Details) - Cash Flow Hedging - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross notional amount outstanding	$ 1,960,000	$ 1,470,000
Derivative asset fair value	3,989	5,402
Derivative liability fair value	$ (10,219)	$ (7,390)
Weighted-average interest rate received	1.58%	1.37%
Weighted-average interest rate paid	1.61%	1.11%
Weighted-average maturity (in years)	2 years 3 months	2 years 9 months 28 days

Derivative Instruments and H124

Derivative Instruments and Hedging Activities - Other Derivative Instruments (Details) - Other Derivative Instruments - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Gross notional amount outstanding		$ 2,665,358	$ 1,656,612
Derivative asset fair value		17,079	13,478
Derivative liability fair value		(14,930)	(13,478)
Fair value of derivative	[1]	$ 15,059	$ 13,753
[1]	This amount represents the fair value if credit risk related contingent factors were triggered.

Derivative Instruments and H125

Derivative Instruments and Hedging Activities - Offsetting Derivatives (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Assets
Gross amounts recognized		$ 21,068	$ 18,880
Less: amounts offset in the Consolidated Statements of Financial Condition		0	0
Net amount presented in the Consolidated Statements of Financial Condition	[1]	21,068	18,880
Offsetting derivative positions		(16,880)	(10,889)
Cash collateral pledged		0	0
Net credit exposure		4,188	7,991
Liabilities
Gross amounts recognized		25,250	21,150
Less: amounts offset in the Consolidated Statements of Financial Condition		0	0
Net amount presented in the Consolidated Statements of Financial Condition	[1]	25,250	21,150
Offsetting derivative positions		(16,880)	(10,889)
Cash collateral pledged		(8,370)	(10,261)
Net credit exposure		$ 0	$ 0
[1]	Included in other assets or other liabilities in the Consolidated Statements of Financial Condition.

Commitments, Guarantees, and126

Commitments, Guarantees, and Contingent Liabilities (Details) - Contractual or Notional Amounts of Financial Instruments - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Other Commitments [Line Items]
Letters of credit		$ 128,801	$ 100,430
Commitments to extend credit
Other Commitments [Line Items]
Commercial, industrial, and agricultural		1,729,426	1,522,152
Commercial real estate		377,551	397,423
Home equity		514,973	426,384
Other commitments	[1]	244,222	214,943
Total commitments to extend credit		$ 2,866,172	$ 2,560,902
[1]	Other commitments includes installment and overdraft protection program commitments.

Fair Value - Recurring Fair Va

Fair Value - Recurring Fair Value Measurements (Details) - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015	[1]	Dec. 31, 2014
Trading securities:
Total trading securities		$ 20,447		$ 17,920
Securities available-for-sale:
Securities available-for-sale, at fair value		1,884,209		1,919,450
Mortgage servicing rights (MSRs)		5,894	[1]	6,120	[1]	$ 1,853		$ 1,728
U.S. treasury securities
Securities available-for-sale:
Securities available-for-sale, at fair value		46,345		48,541
U.S. agency securities
Securities available-for-sale:
Securities available-for-sale, at fair value		156,847		183,637
CMOs
Securities available-for-sale:
Securities available-for-sale, at fair value		1,095,186		1,047,446
MBSs
Securities available-for-sale:
Securities available-for-sale, at fair value		369,543		332,655
Municipal securities
Securities available-for-sale:
Securities available-for-sale, at fair value		208,991		270,846
CDOs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		33,260
Equity securities
Securities available-for-sale:
Securities available-for-sale, at fair value		7,297		3,065
Recurring | Level 1
Trading securities:
Money market funds		1,685		1,645
Mutual funds		18,762		16,275
Total trading securities		20,447		17,920
Securities available-for-sale:
Securities available-for-sale, at fair value		46,345		48,541
Mortgage servicing rights (MSRs)	[2]	0		0
Derivative assets	[2]	0		0
Liabilities
Derivative liabilities	[3]	0		0
Recurring | Level 1 | U.S. treasury securities
Securities available-for-sale:
Securities available-for-sale, at fair value		46,345		48,541
Recurring | Level 1 | U.S. agency securities
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 1 | CMOs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 1 | MBSs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 1 | Municipal securities
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 1 | CDOs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 1 | Equity securities
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 2
Trading securities:
Money market funds		0		0
Mutual funds		0		0
Total trading securities		0		0
Securities available-for-sale:
Securities available-for-sale, at fair value		1,837,864		1,837,649
Mortgage servicing rights (MSRs)	[2]	0		0
Derivative assets	[2]	21,068		18,880
Liabilities
Derivative liabilities	[3]	25,250		21,150
Recurring | Level 2 | U.S. treasury securities
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 2 | U.S. agency securities
Securities available-for-sale:
Securities available-for-sale, at fair value		156,847		183,637
Recurring | Level 2 | CMOs
Securities available-for-sale:
Securities available-for-sale, at fair value		1,095,186		1,047,446
Recurring | Level 2 | MBSs
Securities available-for-sale:
Securities available-for-sale, at fair value		369,543		332,655
Recurring | Level 2 | Municipal securities
Securities available-for-sale:
Securities available-for-sale, at fair value		208,991		270,846
Recurring | Level 2 | CDOs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 2 | Equity securities
Securities available-for-sale:
Securities available-for-sale, at fair value		7,297		3,065
Recurring | Level 3
Trading securities:
Money market funds		0		0
Mutual funds		0		0
Total trading securities		0		0
Securities available-for-sale:
Securities available-for-sale, at fair value		0		33,260
Mortgage servicing rights (MSRs)	[2]	5,894		6,120
Derivative assets	[2]	0		0
Liabilities
Derivative liabilities	[3]	0		0
Recurring | Level 3 | U.S. treasury securities
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 3 | U.S. agency securities
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 3 | CMOs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 3 | MBSs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 3 | Municipal securities
Securities available-for-sale:
Securities available-for-sale, at fair value		0		0
Recurring | Level 3 | CDOs
Securities available-for-sale:
Securities available-for-sale, at fair value		0		33,260
Recurring | Level 3 | Equity securities
Securities available-for-sale:
Securities available-for-sale, at fair value		$ 0		$ 0
[1]	Included in other assets in the Consolidated Statements of Financial Condition.
[2]	Included in other assets in the Consolidated Statements of Financial Condition.
[3]	Included in other liabilities in the Consolidated Statements of Financial Condition.

Fair Value - Significant Unobs

Fair Value - Significant Unobservable Inputs Used In The Valuation of CDOs (Details) - CDOs	12 Months Ended
	Dec. 31, 2016
Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Probability of prepayment	0.00%
Probability of default	16.70%
Loss given default	93.30%
Probability of deferral cure	7.60%
Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Probability of prepayment	10.90%
Probability of default	46.80%
Loss given default	98.90%
Probability of deferral cure	100.00%

Fair Value - Rollforward of Ca

Fair Value - Rollforward of Carrying Value of CDOs (Details) - CDOs - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Rollforward of the Carrying Value of CDOs
Beginning balance		$ 33,260	$ 31,529	$ 33,774
Additions		0	0	0
Change in other comprehensive income (loss)	[1]	14,421	2,337	(2,030)
Paydowns and sales		(47,681)	(606)	(215)
Ending balance		$ 0	$ 33,260	$ 31,529
[1]	Included in unrealized holding gains (losses) in the Consolidated Statements of Comprehensive Income.

Fair Value - Narrative (Detail

Fair Value - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value [Line Items]
Total amount of loans being serviced for the benefit of others at the end of the year	$ 607,016	$ 640,530	$ 242,915
Minimum
Fair Value [Line Items]
Appraisal adjustment (percent)	0.00%
Maximum
Fair Value [Line Items]
Appraisal adjustment (percent)	15.00%

Fair Value - Significant Un131

Fair Value - Significant Unobservable Inputs Used in the Valuation of MSRs (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Minimum
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Prepayment speed	4.20%	7.70%
Maturity (months)	6 months	12 months
Discount rate	9.50%	9.50%
Maximum
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Prepayment speed	13.10%	22.80%
Maturity (months)	92 months	103 months
Discount rate	12.00%	13.00%

Fair Value - Rollforward of132

Fair Value - Rollforward of Carrying Value of MSRs (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Rollforward of Carrying Value of MSRs
Beginning balance		$ 6,120	[1]	$ 1,853	[1]	$ 1,728
Additions from acquisition		0		3,092		0
New MSRs		673		1,263		342
Total (losses) gains included in earnings:
Changes in valuation inputs and assumptions	[2]	(41)		610		(11)
Other changes in fair value	[2],[3]	(858)		(698)		(206)
Ending balance	[1]	5,894		6,120		1,853
Contractual servicing fees earned during the year	[2]	1,536		1,312		546
Total amount of loans being serviced for the benefit of others at the end of the year		$ 607,016		$ 640,530		$ 242,915
[1]	Included in other assets in the Consolidated Statements of Financial Condition.
[2]	Included in mortgage banking income in the Consolidated Statements of Income and related to assets held as of December 31, 2017, 2016, and 2015.
[3]	Primarily represents changes in expected future cash flows over time due to payoffs and paydowns.

Fair Value - Annual Fair Value

Fair Value - Annual Fair Value Measurements of Pension Plan Asses (Details) - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		$ 66,159	[1]	$ 65,189	$ 64,903
Mutual funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	41,002		29,071
U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		13,075		13,904
Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		9,171		7,010
Common stocks
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		7,526
Common trust funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		2,911		7,678
Level 1
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		44,680		42,554
Level 1 | Mutual funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	41,002		29,071
Level 1 | U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		3,678		5,957
Level 1 | Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		0
Level 1 | Common stocks
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		7,526
Level 1 | Common trust funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		0
Level 2
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		21,479		22,635
Level 2 | Mutual funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	0		0
Level 2 | U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		9,397		7,947
Level 2 | Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		9,171		7,010
Level 2 | Common stocks
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		0
Level 2 | Common trust funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		$ 2,911		$ 7,678
[1]	Additional information regarding the fair value of Pension Plan assets as of December 31, 2017 can be found in Note 21, "Fair Value."
[2]	Includes mutual funds, money market funds, cash, cash equivalents, and accrued interest.

Fair Value - Non-Recurring Fai

Fair Value - Non-Recurring Fair Value Measurements (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Fair Value (Details) - Assets Measured On A Non-Recurring Basis [Line Items]
OREO		$ 20,851	$ 26,083
Level 1 | Nonrecurring
Fair Value (Details) - Assets Measured On A Non-Recurring Basis [Line Items]
Collateral-dependent impaired loans	[1]	0	0
OREO	[2]	0	0
Loans held-for-sale	[3]	0	0
Assets held-for-sale	[4]	0	0
Level 2 | Nonrecurring
Fair Value (Details) - Assets Measured On A Non-Recurring Basis [Line Items]
Collateral-dependent impaired loans	[1]	0	0
OREO	[2]	0	0
Loans held-for-sale	[3]	0	0
Assets held-for-sale	[4]	0	0
Level 3 | Nonrecurring
Fair Value (Details) - Assets Measured On A Non-Recurring Basis [Line Items]
Collateral-dependent impaired loans	[1]	33,240	22,019
OREO	[2]	12,340	8,624
Loans held-for-sale	[3]	21,098	10,484
Assets held-for-sale	[4]	$ 2,208	$ 4,075
[1]	Includes impaired loans with charge-offs and impaired loans with a specific reserve during the periods presented.
[2]	Includes OREO with fair value adjustments subsequent to initial transfer that occurred during the periods presented.
[3]	Included in other assets in the Consolidated Statements of Financial Condition.
[4]	Included in premises, furniture, and equipment in the Consolidated Statements of Financial Condition.

Fair Value - Fair Value Measur

Fair Value - Fair Value Measurements of Other Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 192,800	$ 155,055
Interest-bearing deposits in other banks	153,770	107,093
Securities held-to-maturity	13,760	22,291
FHLB and FRB stock	69,708	59,131
Loans	10,342,083	8,168,062
Investment in BOLI	279,900	219,746
Liabilities
Deposits	11,053,325	8,828,603
Borrowed funds	714,884	879,008
Senior and subordinated debt	195,170	194,603
Level 1 | Carrying Amount
Assets
Cash and due from banks	192,800	155,055
Level 1 | Fair Value
Assets
Cash and due from banks	192,800	155,055
Level 2 | Carrying Amount
Assets
Interest-bearing deposits in other banks	153,770	107,093
Securities held-to-maturity	13,760	22,291
FHLB and FRB stock	69,708	59,131
Liabilities
Deposits	11,053,325	8,828,603
Borrowed funds	714,884	879,008
Senior and subordinated debt	195,170	194,603
Accrued interest payable	4,704	3,416
Level 2 | Fair Value
Assets
Interest-bearing deposits in other banks	153,770	107,093
Securities held-to-maturity	12,013	18,212
FHLB and FRB stock	69,708	59,131
Liabilities
Deposits	11,038,819	8,820,572
Borrowed funds	714,884	879,008
Senior and subordinated debt	198,806	197,888
Accrued interest payable	4,704	3,416
Level 3 | Carrying Amount
Assets
Loans	10,345,397	8,172,584
Investment in BOLI	279,900	219,746
Accrued interest receivable	45,261	34,384
Other interest-earning assets	228	834
Level 3 | Fair Value
Assets
Loans	10,059,992	7,973,845
Investment in BOLI	279,900	219,746
Accrued interest receivable	45,261	34,384
Other interest-earning assets	$ 228	$ 834

Related Party Transactions - Na

Related Party Transactions - Narrative (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percent)	5.00%	5.00%

Condensed Parent Company Fin137

Condensed Parent Company Financial Statements - Statements of Financial Condition (Parent Company Only) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and due from banks	$ 192,800	$ 155,055
Other assets	221,451	278,271
Total assets	14,077,052	11,422,555
Liabilities and Stockholders' Equity
Senior and subordinated debt	195,170	194,603
Accrued interest payable and other liabilities	248,799	263,261
Stockholders' equity	1,864,874	1,257,080	$ 1,146,268	$ 1,100,775
Total liabilities and stockholders' equity	14,077,052	11,422,555
Parent Company
Assets
Cash and due from banks	120,812	140,217
Investments in and advances to subsidiaries	1,952,414	1,279,065
Other assets	43,606	139,060
Total assets	2,116,832	1,558,342
Liabilities and Stockholders' Equity
Senior and subordinated debt	195,170	194,603
Accrued interest payable and other liabilities	56,788	106,659
Stockholders' equity	1,864,874	1,257,080
Total liabilities and stockholders' equity	$ 2,116,832	$ 1,558,342

Condensed Parent Company Fin138

Condensed Parent Company Financial Statements - Statements of Income (Parent Company Only) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income
Interest income	$ 509,716	$ 378,332	$ 335,984
Securities transactions and other	3,913	3,635	2,764
Expenses
Interest expense	37,712	28,641	24,386
Other expenses	31,821	24,834	21,601
Income before income tax expense	187,954	138,520	119,811
Income tax benefit	(89,567)	(46,171)	(37,747)
Net income	98,387	92,349	82,064
Net income applicable to non-vested restricted shares	(916)	(1,043)	(882)
Net income applicable to common shares	97,471	91,306	81,182
Parent Company
Income
Dividends from subsidiaries	74,091	86,791	127,000
Interest income	2,211	2,188	2,164
Securities transactions and other	(1,372)	215	584
Total income	74,930	89,194	129,748
Expenses
Interest expense	12,428	12,477	12,545
Salaries and employee benefits	20,978	16,104	14,624
Other expenses	9,126	7,110	6,003
Total expenses	42,532	35,691	33,172
Income before income tax expense	32,398	53,503	96,576
Income tax benefit	14,851	12,878	11,950
Income before equity in undistributed income (loss) of subsidiaries	47,249	66,381	108,526
Equity in undistributed income (loss) of subsidiaries	51,138	25,968	(26,462)
Net income	98,387	92,349	82,064
Net income applicable to non-vested restricted shares	(916)	(1,043)	(882)
Net income applicable to common shares	$ 97,471	$ 91,306	$ 81,182

Condensed Parent Company Fin139

Condensed Parent Company Financial Statements - Statements of Cash Flows (Parent Company Only) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities
Net income		$ 98,387	$ 92,349	$ 82,064
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises, furniture, and equipment		13,995	12,804	13,367
Net securities losses (gains)		1,876	(1,420)	(2,373)
Share-based compensation expense	[1]	11,223	7,879	7,242
Tax benefit (expense) related to share-based compensation		349	(197)	(406)
Net decrease (increase) in other assets		121,577	(76,902)	10,023
Net (decrease) increase in other liabilities		(55,762)	47,118	(1,042)
Investing Activities
Purchases of securities available-for-sale		(733,440)	(933,317)	(509,481)
Purchases of premises, furniture, and equipment		(16,123)	(19,083)	(11,269)
Net cash paid for acquisitions		41,717	57,347	(16,047)
Net cash used in investing activities		(145,780)	(1,049,338)	(496,834)
Financing Activities
Net proceeds from the issuance of subordinated debt		0	146,484	0
Payments for the retirement of senior and subordinated debt		0	(153,500)	0
Treasury stock activity		0	0	120
Cash dividends paid		(37,129)	(29,198)	(27,036)
Restricted stock activity		(3,952)	(2,476)	(2,890)
Net cash used in financing activities		(4,357)	808,750	114,023
Net (decrease) increase in cash and cash equivalents		84,422	(119,054)	(225,060)
Cash and cash equivalents at beginning of year		262,148	381,202	606,262
Cash and cash equivalents at end of year		346,570	262,148	381,202
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		534,090	54,896	0
Parent Company
Operating Activities
Net income		98,387	92,349	82,064
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed (income) loss of subsidiaries		(51,138)	(25,968)	26,462
Depreciation of premises, furniture, and equipment		9	2	7
Net securities losses (gains)		1,523	0	(1)
Share-based compensation expense		11,223	7,879	7,242
Tax benefit (expense) related to share-based compensation		349	(197)	(406)
Net decrease (increase) in other assets		18,667	(75,104)	23,699
Net (decrease) increase in other liabilities		(52,377)	74,571	(17,132)
Net cash provided by operating activities		26,643	73,532	121,935
Investing Activities
Purchases of securities available-for-sale		0	(14)	0
Proceeds from sales and maturities of securities available-for-sale		42,516	601	310
Purchases of premises, furniture, and equipment		(119)	0	(5)
Net cash paid for acquisitions		(47,364)	(14,905)	(16,047)
Net cash used in investing activities		(4,967)	(14,318)	(15,742)
Financing Activities
Net proceeds from the issuance of subordinated debt		0	146,484	0
Payments for the retirement of senior and subordinated debt		0	(153,500)	0
Treasury stock activity		0	0	(120)
Cash dividends paid		(37,129)	(29,198)	(27,036)
Restricted stock activity		(3,952)	(2,476)	(2,890)
Net cash used in financing activities		(41,081)	(38,690)	(30,046)
Net (decrease) increase in cash and cash equivalents		(19,405)	20,524	76,147
Cash and cash equivalents at beginning of year		140,217	119,693	43,546
Cash and cash equivalents at end of year		120,812	140,217	119,693
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		$ 534,090	$ 54,896	$ 0
[1]	Comprised of restricted stock, restricted stock unit, and performance share awards expense.