MB Financial 10-K 27 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 26, 2015	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name	MB FINANCIAL INC /MD
Entity Central Index Key	1139812
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$1,446,208,206
Entity Common Stock, Shares Outstanding		75,193,005
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets
Cash and due from banks	$256,804	$205,193
Interest earning deposits with banks	55,277	268,266
Total cash and cash equivalents	312,081	473,459
Federal funds sold	0	42,950
Investment securities:
Securities available for sale, at fair value	1,654,752	1,118,912
Securities held to maturity, at amortized cost ($1,035,061 and $1,198,929 fair value at December 31, 2014 and 2013, respectively)	993,380	1,182,533
Non-marketable securities - FHLB and FRB stock	75,569	51,417
Total investment securities	2,723,701	2,352,862
Loans held for sale	737,209	629
Loans:
Total loans, excluding purchased credit impaired and covered loans	8,831,572	5,476,831
Purchased credit impaired and covered loans	251,645	235,720
Total loans	9,083,217	5,712,551
Less: Allowance for loan and lease losses	110,026	111,746
Net loans	8,973,191	5,600,805
Lease investment, net	162,833	131,089
Premises and equipment, net	238,377	221,065
Cash surrender value of life insurance	133,562	130,181
Goodwill	711,521	423,369
Other intangibles	38,006	23,428
Mortgage servicing rights, at fair value	235,402	413
Other real estate owned, net	19,198	23,289
Other real estate owned related to FDIC-assisted transactions	19,328	20,472
Other assets	297,690	197,416
Total assets	14,602,099	9,641,427
Deposits:
Non-interest bearing	4,118,256	2,375,863
Interest bearing	6,872,686	5,005,396
Total deposits	10,990,942	7,381,259
Short-term borrowings	931,415	493,389
Long-term borrowings	82,916	62,159
Junior subordinated notes issued to capital trusts	185,778	152,065
Accrued expenses and other liabilities	382,762	225,873
Total liabilities	12,573,813	8,314,745
STOCKHOLDERS’ EQUITY
Preferred stock, ($0.01 par value, authorized 10,000,000 shares at December 31, 2014 and 1,000,000 at December 31, 2013; Series A, 8% perpetual non-cumulative, 4,000,000 shares issued and outstanding at December 31, 2014 and no shares outstanding at December 31, 2013, $25 liquidation value)	115,280	0
Common stock, ($0.01 par value; authorized 100,000,000 shares at December 31, 2014 and 70,000,000 at December 31, 2013; issued 75,067,482 shares at December 31, 2014 and 55,148,409 shares at December 31, 2013)	751	551
Additional paid-in capital	1,267,761	738,053
Retained earnings	629,677	581,998
Accumulated other comprehensive income	20,356	8,383
Less: 296,715 and 184,173 shares of treasury stock, at cost, at December 31, 2014 and 2013, respectively	-6,974	-3,747
Controlling interest stockholders’ equity	2,026,851	1,325,238
Noncontrolling interest	1,435	1,444
Total stockholders’ equity	2,028,286	1,326,682
Total liabilities and stockholders’ equity	$14,602,099	$9,641,427

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Securities held to maturity, at amortized cost, fair value (in dollars)	$1,035,061	$1,198,929
Preferred stock, par value	$0.01	$0.01
Preferred stock, shares authorized	10,000,000	1,000,000
Preferred stock, dividend rate	8.00%
Preferred stock, shares issued	4,000,000	0
Preferred stock, shares outstanding	4,000,000	0
Preferred stock, liquidation preference per share	$25	$0
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, authorized shares	100,000,000	70,000,000
Common stock, issued shares	75,067,482	55,148,409
Treasury stock, shares	296,715	184,173

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Loans:
Taxable	$292,028		$228,931		$263,079
Nontaxable	9,022		9,611		8,629
Investment securities:
Taxable	38,619		26,084		33,424
Nontaxable	34,791		32,564		29,311
Federal funds sold	25		15
Other interest earning accounts	663		690		867
Total interest income	375,148		297,895		335,310
Interest expense:
Deposits	17,027		19,240		30,258
Short-term borrowings	780		622		1,204
Long-term borrowings and junior subordinated notes	6,518		5,697		11,060
Total interest expense	24,325		25,559		42,522
Net interest income	350,823		272,336		292,788
Provision for credit losses	12,052		-5,804		-8,900
Net interest income after provision for credit losses	338,771		278,140		301,688
Non-interest income:
Lease financing, net	64,310		61,243		36,382
Mortgage banking revenue	46,149		1,664		2,325
Commercial deposit and treasury management fees	34,315		24,867		23,636
Trust and asset management fees	21,839		19,142		17,990
Card fees	13,741		11,013		9,368
Capital markets and international banking fees	5,458		3,560		5,086
Consumer and other deposit service fees	12,788		13,968		14,428
Brokerage fees	5,176		4,907		4,792
Loan service fees	4,814		5,563		5,845
Increase in cash surrender value of life insurance	3,381		3,385		3,570
Net (loss) gain on investment securities	-2,525		-1		555
Net gain (loss) on sale of assets	3,452		-323		-942
Gain on extinguishment of debt	1,895		0		0
Other operating income	6,512		5,406		6,158
Total non-interest income	221,305		154,394		129,193
Non-interest expenses:
Salaries and employee benefits	255,974		177,858		165,696
Occupancy and equipment expense	44,910		36,878		35,806
Computer services and telecommunication expense	31,678		18,883		15,499
Advertising and marketing expense	8,854		8,272		8,183
Professional and legal expense	14,652		8,807		6,110
Other intangibles amortization expense	5,501		6,084		5,010
Facilities impairment charges	2,270				2,190
Net loss (gain) recognized on other real estate owned and other related expense	3,575		-781		20,584
Prepayment fees on interest bearing liabilities					12,682
Other operating expenses	69,368		38,587		32,270
Total non-interest expenses	436,782	[1]	294,588	[1]	304,030
Income before income taxes	123,294		137,946		126,851
Income tax expense	37,193		39,491		36,477
Net income	86,101		98,455		90,374
Dividends and discount accretion on preferred shares	4,000				3,269
Net income available to common stockholders	$82,101		$98,455		$87,105
Common share data:
Basic earnings per common share (dollars per share)	$1.32		$1.81		$1.61
Diluted earnings per common share (dollars per share)	$1.31		$1.79		$1.60
Weighted average common shares outstanding for basic earnings per common share (in shares)	62,012,196		54,509,612		54,270,297
Diluted weighted average common shares outstanding for diluted earnings per common share (in shares)	62,573,406		54,993,865		54,505,976
[1]	Includes merger related expenses of $34.8 million and $2.5 million in the banking segment for the years ended December 31, 2014 and 2013, respectively.

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$86,101	$98,455	$90,374
Unrealized holding gains (losses) on investment securities, net of reclassification adjustments	20,933	-43,543	-4,097
Reclassification adjustment for amortization of unrealized gains on investment securities transferred to held to maturity from available for sale	-3,700	-2,478	0
Reclassification adjustments for losses (gains) included in net income	2,525	1	-555
Other comprehensive income (loss), before tax	19,758	-46,020	-4,652
Income tax (expense) benefit related to items of other comprehensive income (loss)	-7,785	18,077	1,828
Other comprehensive income (loss), net of tax	11,973	-27,943	-2,824
Comprehensive income	$98,074	$70,512	$87,550

CONSOLIDATED_STATEMENTS_OF_CHA

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (USD $)	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss), Net of Tax	Treasury Stock	Noncontrolling Interest
In Thousands, unless otherwise specified
Balance at Dec. 31, 2011	$1,393,027	$194,719	$548	$731,248	$427,956	$39,150	($3,044)	$2,450
Increase (Decrease) in Stockholders' Equity
Net income	90,604				90,374			230
Other comprehensive income (loss), net of tax	-2,824					-2,824
Cash dividends declared on common stock	-7,149				-7,149
Dividends and discount accretion on preferred shares	-1,988	1,281			-3,269
Repurchase of preferred shares and warrant	-197,518	-196,000		-1,518
Restricted common stock activity, net of tax	1,090		2	-704	18		1,774
Stock option activity, net of tax	-346			-694	3		345
Repurchase of common shares in connection with employee benefit plans and held in trust for deferred compensation plan	-1,999			369			-2,368
Stock-based compensation expense	4,806			4,806
Additional investment in subsidiary	-1,640			-736				-904
Distributions to noncontrolling interest	-293							-293
Balance at Dec. 31, 2012	1,275,770	0	550	732,771	507,933	36,326	-3,293	1,483
Increase (Decrease) in Stockholders' Equity
Net income	98,641				98,455			186
Other comprehensive income (loss), net of tax	-27,943					-27,943
Cash dividends declared on common stock	-24,290				-24,290
Restricted common stock activity, net of tax	887		1	-739	-100		1,725
Stock option activity, net of tax	557			58			499
Repurchase of common shares in connection with employee benefit plans and held in trust for deferred compensation plan	-2,171			507			-2,678
Stock-based compensation expense	5,456			5,456
Distributions to noncontrolling interest	-225							-225
Balance at Dec. 31, 2013	1,326,682	0	551	738,053	581,998	8,383	-3,747	1,444
Increase (Decrease) in Stockholders' Equity
Net income	86,392				86,101			291
Other comprehensive income (loss), net of tax	11,973					11,973
Issuance of preferred stock	115,280	115,280
Issuance of common stock due to business combination	518,992		196	518,796
Cash dividends declared on preferred shares	-4,000				-4,000
Cash dividends declared on common stock	-34,422				-34,422
Restricted common stock activity, net of tax	874		2	812			60
Stock option activity, net of tax	531		2	529
Repurchase of common shares in connection with employee benefit plans and held in trust for deferred compensation plan	-2,690			597			-3,287
Stock-based compensation expense	8,974			8,974
Distributions to noncontrolling interest	-300							-300
Balance at Dec. 31, 2014	$2,028,286	$115,280	$751	$1,267,761	$629,677	$20,356	($6,974)	$1,435

CONSOLIDATED_STATEMENTS_OF_CHA1

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Stockholders' Equity [Abstract]
Cash dividends declared	$0.52	$0.44	$0.13

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows From Operating Activities
Net income	$86,101	$98,455	$90,374
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises and equipment and leased equipment	60,067	51,893	52,419
Facilities impairment charges	2,270		2,190
Compensation expense for share-based payment plans	8,974	5,456	4,806
(Gain) loss on sales of premises and equipment and leased equipment	-5,817	362	-2,204
Amortization of other intangibles	5,501	6,084	5,010
Provision for credit losses	12,052	-5,804	-8,900
Deferred income tax expense	-48	21,681	15,177
Amortization of premiums and discounts on investment securities, net	45,413	47,771	44,543
Accretion of premiums and discounts on loans, net	-21,262	-7,122	-13,797
Accretion of FDIC indemnification asset	-112	-342	-1,055
Net loss (gain) on investment securities	2,525	1	-555
Proceeds from sale of loans held for sale	2,213,914	86,505	96,243
Origination of loans held for sale	-2,266,636	-77,935	-96,480
Net gain on sale of loans held for sale	-12,022	-1,664	-2,325
Change in fair value of mortgage servicing rights	11,777	0	0
Net loss (gain) on other real estate owned	1,554	-1,888	14,503
Net loss on other real estate owned related to FDIC-assisted transactions	446	360	3,091
Increase in cash surrender value of life insurance	-3,381	-3,385	-3,570
Gain on extinguishment of debt	-1,895	0	0
Decrease (increase) in other assets, net	9,988	17,485	-67,511
Increase (decrease) in other liabilities, net	18,038	-45,155	49,861
Net cash provided by operating activities	167,447	192,758	181,820
Cash Flows From Investing Activities
Decrease (increase) in federal funds sold	42,950	-42,950	0
Proceeds from sales of investment securities available for sale	512,878	989	15,416
Proceeds from maturities and calls of investment securities available for sale	259,694	496,258	608,665
Purchase of investment securities available for sale	-216,777	-484,113	-605,098
Proceeds from maturities and calls of investment securities held to maturity	41,654	17,087	2,134
Purchase of investment securities held to maturity	-122,859	-61,073	-2,187
Purchase of non-marketable securities - FHLB and FRB stock	-15	-547	-44
Redemption of non-marketable securities - FHLB and FRB stock	26,483	4,515	25,491
Net decrease in loans	155,399	38,725	219,125
Purchases in mortgage servicing rights	-1,096	0	0
Purchases of premises and equipment and leased equipment	-94,667	-65,453	-76,675
Proceeds from sales of premises and equipment and leased equipment	22,924	8,532	14,587
Capital improvements on other real estate owned	0	-74	-2,809
Proceeds from sale of other real estate owned	9,390	21,814	34,316
Proceeds from sale of other real estate owned related to FDIC-assisted transactions	17,049	15,194	40,298
Life insurance death benefit		2,083
Net cash acquired (paid) in business acquisition	25,174	0	-27,010
Net (payments for) proceeds from FDIC related covered assets	-3,620	9,766	83,954
Net cash provided by (used in) investing activities	674,561	-39,247	330,163
Cash Flows From Financing Activities
Net decrease in deposits	-343,530	-161,438	-104,910
Net (decrease) increase in short-term borrowings	-597,774	272,787	648
Proceeds from long-term borrowings	33,816	7,725	6,742
Principal paid on long-term borrowings	-13,059	-61,616	-156,956
Redemption of junior subordinated notes issued to capital trusts	-45,369	0	-6,186
Repurchase of preferred stock and warrant	0	0	-197,518
Treasury stock transactions, net	-2,690	-1,672	-249
Stock options exercised	1,034	1,014	154
Excess tax benefits from share-based payment arrangements	396	-325	-390
Dividends paid on preferred stock	-2,000		-3,239
Dividends paid on common stock	-34,210	-24,070	-7,101
Net cash (used in) provided by financing activities	-1,003,386	32,405	-469,005
Net (decrease) increase in cash and cash equivalents	-161,378	185,916	42,978
Cash and cash equivalents:
Beginning of year	473,459	287,543	244,565
End of year	312,081	473,459	287,543
Cash payments for:
Interest paid to depositors and other borrowed funds	25,258	26,345	44,212
Net income tax payments, net	23,040	35,375	9,883
Supplemental Schedule of Noncash Investing Activities:
Investment securities held to maturity purchased not settled	0	321	0
Transfer of investment securities available for sale to investment securities held to maturity	0	656,617	0
Transfer of investment securities held to maturity to investment securities available for sale		0	0
Loans transferred to other real estate owned	2,133	6,164	4,535
Loans transferred to other real estate owned related to FDIC-assisted transactions	16,337	16,023	19,705
Loans transferred to repossessed vehicles	1,019	871	1,496
Operating leases rewritten as direct finance leases included as loans	5,853	6,936	7,760
Noncash assets acquired:
Investment securities available for sale	826,691		635
Investment securities held to maturity	22,599	0	0
Non-marketable securities -FHLB and FRB stock	50,620	0	0
Loans held for sale	670,671	0	0
Loans	3,532,211		32,933
Lease investments	11,885	0	0
Premises and equipment	19,701		81
Goodwill	288,152		36,300
Other intangibles	20,079		5,028
Mortgage servicing rights	224,453	0	0
Other real estate owned	4,720	0	0
Other assets	130,478		27,323
Total noncash assets acquired	5,802,260	0	102,300
Liabilities assumed:
Deposits	3,953,213	0	0
Short-term borrowings	1,035,800	0	0
Junior subordinated notes issued to capital trusts	80,843	0	0
Other liabilities	123,028		75,290
Total liabilities assumed	$5,192,884	$0	$75,290

Significant_Accounting_Policie

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies
	MB Financial, Inc. (the "Company," "we," "us," "our") is a financial holding company that provides a full range of financial services to individuals and corporate customers through its banking subsidiary, MB Financial Bank, N.A. ("MB Financial Bank").
	The Company’s primary market is the Chicago, Illinois metropolitan area, in which MB Financial Bank operates 86 banking offices through MB Financial Bank.
	MB Financial Bank, our largest subsidiary, has three wholly owned subsidiaries with significant operating activities: LaSalle Systems Leasing, Inc., Celtic Leasing Corp. Cole Taylor Equipment Finance, LLC. MB Financial Bank also has a majority owned subsidiary with significant operating activities, Cedar Hill Associates, LLC. Vision Investment Services, Inc., a subsidiary of MB Financial Bank, was dissolved in the fourth quarter of 2012.
	Basis of Financial Statement Presentation: The consolidated financial statements include the accounts of the Company and its subsidiaries.  Significant intercompany items and transactions have been eliminated in consolidation.  The accounting and reporting policies of the Company conform to accounting principles generally accepted in the United States of America and general practices within the financial services industry.  In accordance with applicable accounting standards, the Company does not consolidate statutory trusts established for the sole purpose of issuing trust preferred securities and related trust common securities.  See Note 12 below for more detail.  In preparing the financial statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and revenues and expenses for the year.  Actual results could differ from those estimates.  Areas involving the use of management’s estimates and assumptions, which are more susceptible to change in the near term include the allowance for loan and lease losses; residual value of direct finance, leveraged, and operating leases; valuation of mortgage servicing rights; income tax accounting; fair value measurements for assets and liabilities; and goodwill.
	Cash and cash equivalents: For purposes of reporting cash flows, cash and cash equivalents includes cash on hand, amounts due from banks (including cash items in process of clearing), interest-bearing deposits with banks, with original maturities of 90 days or less.
	Investment securities: Securities classified as available for sale are those securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity.  Any decision to sell a security classified as available for sale is based on various factors, including movements in interest rates, changes in the maturity mix of assets and liabilities, liquidity needs, regulatory capital considerations, and other factors.  Securities available for sale are reported at fair value with unrealized gains or losses reported as accumulated other comprehensive income, net of the related deferred tax effect.  Securities classified as held to maturity are those securities that the Company intends to hold until maturity and are reported at amortized cost.
	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 level-yield method.  In determining the estimated life of a mortgage-related security, certain judgments are required as to the timing and amount of future principal prepayments.  These judgments are made based upon the actual performance of the underlying security and the general market consensus regarding changes in mortgage interest rates and underlying prepayment estimates.  Amortization of premium and accretion of discount is included in interest income from the related security.  Realized gains or losses, determined on the basis of the cost of specific securities sold, are included in earnings.
	The Company evaluates the portfolio for impairment each quarter.  In estimating other-than-temporary losses, the Company considers the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer, and whether the Company is more likely than not to sell the security before recovery of its cost basis.  If the Company intends to sell an impaired security, the Company records an other-than-temporary loss in an amount equal to the entire difference between the fair value and amortized cost.  If a security is determined to be other-than-temporarily impaired, but the Company does not intend to sell the security, only the credit portion of the estimated loss is recognized in earnings, with the other portion of the loss recognized in other comprehensive income.
	Federal Home Loan Bank and Federal Reserve Bank stock: The Company owns investments in the stock of the Federal Reserve Bank of Chicago (“FRB”) and the Federal Home Loan Bank of Chicago (“FHLB”). No ready market exists for these stocks, and they have no quoted market values. The Bank, as a member of the Federal Reserve System and the FHLB, is required to maintain an investment in the capital stock of the FRB and FHLB. The stock is redeemable at par by the FRB and FHLB, respectively, and is, therefore, carried at cost and periodically evaluated for impairment.
	Loans held for sale: Mortgage loans originated and intended for sale in the secondary market are reflected at fair value.  Changes in the fair value are recognized in mortgage banking revenue on the Company's Consolidated Statements of Operations.
	Mortgage Loan Representation and Warranty Reserve: The Company originates and sells residential mortgage loans in the secondary market. When the Company sells mortgage loans, it makes customary representations and warranties to the purchasers about various characteristics of each loan, such as the ownership of the loan, the validity of the lien securing the loan, the nature and extent of underwriting standards applied and the types of documentation being provided. These representations and warranties are generally enforceable over the life of the loan. If a defect in the origination process is identified, the Company may be required to either repurchase the loan or indemnify the purchaser for losses it sustains on the loan. If there are no such defects, the Company has no liability to the purchaser for losses it may incur on such loans.
	The Company maintains a representation and warranty reserve to account for the expected losses related to loans it might be required to repurchase or the indemnity payments it may have to make to purchasers. The representation and warranty reserve reflects management's best estimate of probable lifetime loss. The reserve considers both the estimate of expected losses on loans sold during the current accounting period as well as adjustments to the Company's previous estimate of expected losses on loans sold. Factors considered include borrower performance, repurchase demand behavior, and historical loan defect experience. Management monitors the adequacy of the overall reserve and makes adjustments to the level of reserve, as necessary, after consideration of other qualitative factors.
	At the time a loan is funded, the representation and warranty reserve is recorded as a decrease in mortgage banking revenue on the Consolidated Statements of Operations and recorded in accrued interest, taxes and other liabilities on the Company's Consolidated Balance Sheets. Changes to the reserve are recorded as an increase or decrease to mortgage banking revenue on the Consolidated Statements of Operations.
	Loans and leases: Loans are stated at the amount of unpaid principal reduced by the allowance for loan and lease losses and unearned income.  Direct finance and leveraged leases are included as lease loans for financial statement purposes.  Direct finance leases are stated as the sum of remaining minimum lease payments from lessees plus estimated residual values less unearned lease income.  Leveraged leases are stated at the sum of remaining minimum lease payments from lessees (less nonrecourse debt payments) plus estimated residual values less unearned lease income.  On a quarterly basis, management reviews the lease residuals for potential impairment.  Unearned lease income on direct finance and leveraged leases is recognized over the lives of the leases using the level-yield method.
	Loan origination and commitment fees and certain direct loan origination costs are deferred and the net amount amortized as an adjustment of the related loan’s yield.  The Company is amortizing these amounts over the contractual life of the loan.  Commitment fees based upon a percentage of a customer’s unused line of credit and fees related to standby letters of credit are recognized over the commitment period.
	Interest income is accrued daily on the Company’s outstanding loan balances.  The accrual of interest on loans is discontinued at the time the loan is 90 days past due unless the credit is well-secured and in process of renewal or collection.  Past due status is based on contractual terms of the loan.  In all cases, loans are placed on non-accrual or charged-off at an earlier date if collection of principal or interest is considered doubtful.  All interest accrued but not collected for loans that are placed on non-accrual or charged-off is reversed against interest income.
	For impaired loans, accrual of interest is discontinued on a loan when management believes, after considering collection efforts and other factors, the borrower’s financial condition is such that collection of interest is doubtful.  Cash collections on impaired loans are generally credited to the loan balance, and no interest income is recognized on those loans until the principal balance has been determined to be collectible.  Loans, other than those included in large groups of smaller-balance homogeneous loans, are considered impaired when it is probable the Company will be unable to collect all contractual principal and interest payments due in accordance with the terms of the loan agreement.  Impaired loans include non-accrual loans and loans classified as a troubled debt restructuring. Impaired loans are measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate or, as a practical expedient, based on the loan’s observable market price or the fair value of the collateral if the loan is collateral dependent.  The amount of impairment, if any and any subsequent changes are charged against the allowance for loan and lease losses.
	Troubled debt restructurings:  A loan is classified as a troubled debt restructuring when a borrower is experiencing financial difficulties that leads to a restructuring of the loan, and the Company grants concessions to the borrower in the restructuring that it would not otherwise consider. These concessions may include rate reductions, principal forgiveness, deferral of past due interest or principal, extension of maturity date, modification of amortization schedules, redemption of past due taxes and other actions intended to minimize potential losses.
	In determining whether a debtor is experiencing financial difficulties, the Company considers if the debtor is in payment default or would be in payment default in the foreseeable future without the modification, the debtor declared or is in the process of declaring bankruptcy, there is substantial doubt that the debtor will continue as a going concern, the debtor has securities that have been or are in the process of being delisted, the debtor’s entity-specific projected cash flows will not be sufficient to service any of its debt, or the debtor cannot obtain funds from sources other than the existing creditors at a market rate for debt with similar risk characteristics.
	In determining whether the Company has granted a concession, the Company assesses, if it does not expect to collect all amounts due, whether the current value of the collateral will satisfy the amounts owed, whether additional collateral or guarantees from the debtor will serve as adequate compensation for other terms of the restructuring, and whether the debtor otherwise has access to funds at a market rate for debt with similar risk characteristics.
	A loan that is modified at a market rate of interest will not be classified as troubled debt restructuring in the calendar year subsequent to the restructuring if it is in compliance with the modified terms.  Payment performance prior and subsequent to the restructuring is taken into account in assessing whether it is likely that the borrower can meet the new terms.  Under certain circumstances, a loan may be returned to accrual at the time of restructuring.  A period of sustained repayment for at least six months generally is required for return to accrual status.
	Periodically, the Company will restructure a note into two separate notes (A/B structure), charging off the entire B portion of the note. The A note is structured with appropriate loan-to-value and cash flow coverage ratios that provide for a high likelihood of repayment. The A note is classified as a non-performing note until the borrower has displayed a historical payment performance for a reasonable time prior to and subsequent to the restructuring. A period of sustained repayment for at least six months generally is required to return the note to accrual status provided that management has determined that the performance is reasonably expected to continue. The A note will be classified as a restructured note (either performing or non-performing) through the calendar year of the restructuring that the historical payment performance has been established.
	Allowance for loan and lease losses:  The allowance for loan and lease losses (ALLL) is established through a provision for credit losses charged to expense.  Loans are charged against the ALLL when management believes that collectability of the principal is unlikely.  The allowance is an amount that management believes will be appropriate to absorb probable losses on existing loans, based on an evaluation of the collectability of loans and prior loss and recovery experience as appropriate under GAAP.  The ALLL is based on management’s evaluation of the loan portfolio giving consideration to the nature and volume of the loan portfolio, the value of underlying collateral, overall portfolio quality, review of specific problem loans, and prevailing economic conditions that may affect the borrower’s ability to pay.  While management uses the best information available to make its evaluation, future adjustments to the allowance may be necessary if there are significant changes in economic conditions.  In addition, regulatory agencies, as an integral part of their examination process, periodically review MB Financial Bank’s ALLL, and may require it to recognize adjustments to its allowance based on their judgments of information available to them at the time of their examinations.
	The ALLL is comprised of three elements: a commercial related general loss reserve; a commercial related specific reserve for impaired loans; and a consumer related reserve for smaller-balance homogenous loans.  Each element is discussed below.
	Commercial Related General Loss Reserve - We maintain a general loan loss reserve for the four categories of commercial related loans in our portfolio - commercial loans, commercial loans collateralized by the assignment of lease payments (lease loans), commercial real estate loans and construction real estate loans.
	Under our loan risk rating system, each loan, with the exception of those included in large groups of smaller-balance homogeneous consumer related loans, is risk rated between one and nine by the originating loan officer, Senior Credit Management, Loan Review or loan committee.  Loans rated "one" represent those loans least likely to default and a loan rated "nine" represents a loss.  The probability of loans defaulting for each risk rating, sometimes referred to as default factors, are estimated based on the frequency with which loans migrate from one risk rating to another and to default status over time.  We use a loan loss reserve model that incorporates the migration of loan risk ratings and historical default data over a multi-year period to develop our estimated default factors (EDFs).  The model tracks annual loan rating migrations by loan type and currently uses loan risk rating migrations for 14 years.  The migration data is adjusted by using average losses for an economic cycle (approximately 13 years) to develop EDFs by loan type, risk rating and maturity.  EDFs are updated annually in December.
	Estimated loan default factors are multiplied by individual loan balances in each risk-rating category and again multiplied by an historical loss given default estimate for each loan type (which incorporates estimated recoveries) to determine the appropriate allowance by loan type.  This approach is applied to the commercial, lease, commercial real estate, and construction real estate components of the portfolio.
	To account for current economic conditions, the general allowance for loan and lease losses also includes adjustments for macroeconomic factors.  Macroeconomic factors adjust the ALLL upward or downward based on the current point in the economic cycle using predictive economic data and are applied to the loan loss model through a separate allowance element for the commercial, commercial real estate, construction real estate and lease loan components.  To determine our macroeconomic factors, we use specific economic data that has shown to be a statistically reliable predictor of our credit losses relative to our long term average credit losses. We tested over 20 economic variables (U.S. manufacturing index, unemployment rate, U.S. GDP growth, etc.). We annually review this data to determine that such a relationship continues to exist. We currently use the following macroeconomic indicators in our macroeconomic factor computation:
	Commercial loans and lease loans:  initial unemployment insurance claims in Illinois, our prior period charge-off rates and crude oil prices.
	Commercial real estate loans and construction loans:  M2 Money stock, our prior period charge-off rates and the U.S. commercial real estate index.
	Using the indicators noted above, a predicted charge-off percentage is calculated.  The predicted charge-off percentage is then compared to the cycle average charge-off percentage, and a macroeconomic adjustment factor is calculated.  The macroeconomic adjustment factor is applied to each commercial loan type.  Each year, we review the predictive nature of the macroeconomic factors by comparing actual charge-offs to the predicted model charge-offs, re-run our regression analysis and re-calibrate the macroeconomic factors as appropriate.
	Commercial Related Specific Reserves - The ALLL also includes specific reserves on impaired commercial related loans.  A loan is considered to be impaired when management believes, after considering collection efforts and other factors, the borrower’s financial condition is such that the collection of all contractual principal and interest payments due is doubtful.
	At each quarter-end, impaired loans are reviewed individually, with adjustments made to the general calculated reserve for each loan as deemed necessary.  Specific adjustments are made depending on expected cash flows and/or the value of the collateral securing each loan.  Generally, the Company obtains a current external appraisal (within 12 months) on real estate secured impaired loans.  Our appraisal policy is designed to comply with the Interagency Appraisal and Evaluation Guidelines, most recently updated in December 2010. As part of our compliance with these guidelines, we maintain an internal Appraisal Review Department that engages and reviews all third party appraisals.
	In addition, each impaired commercial loan with real estate collateral is reviewed quarterly by our appraisal department to determine that the most recent valuation remains appropriate during subsequent quarters until the next appraisal is received.  If considered necessary by our appraisal department, the appraised value may be further discounted to reflect current values.
	Other valuation techniques are also used to value non-real estate assets.  Discounts may be applied in the impairment analysis used for general business assets (GBA).  Examples of GBA include accounts receivable, inventory, and any marketable securities pledged. The discount is used to reflect collection risk in the event of default that may not have been included in the valuation of the asset.
	Consumer Related Reserves - Pools of homogeneous loans with similar risk and loss characteristics are also assessed for probable losses.  These loan pools include consumer, residential real estate, home equity, credit cards and indirect vehicle loans.  Migration probabilities obtained from past due roll rate analyses and historical loss rates are applied to current balances to forecast charge-offs over a one-year time horizon.
	We consistently apply our methodology for determining the appropriateness of the allowance for loan and lease losses but may adjust our methodologies and assumptions based on historical information related to charge-offs and management's evaluation of the loan portfolio. In this regard, we periodically review the following to validate our allowance for loan and lease losses: historical net charge-offs as they relate to prior periods' allowance for loan and lease loss, comparison of historical loan migration in past years compared to the current year, overall credit trends and ratios and any significant changes in loan concentrations. In reviewing this data, we adjust qualitative factors within our allowance methodology to appropriately reflect any changes warranted by the validation process.
	Acquired loans: Purchased loans acquired in a business combination are recorded at estimated fair value on their purchase date without a carryover of the related allowance for loan and lease losses. These acquired loans are segregated into three types: pass rated loans with no discount attributable to credit quality, non-impaired loans with a discount attributable at least in part to credit quality and impaired loans with evidence of significant credit deterioration.
	•	Pass rated loans (typically performing loans) are accounted for in accordance with ASC 310-20 "Nonrefundable Fees and Other Costs" as these loans do not have evidence of credit deterioration since origination.
	•	Non-impaired loans (typically performing substandard loans) are accounted for in accordance with ASC 310-30 if they display at least some level of credit deterioration since origination.
	•	Impaired loans (typically substandard loans on non-accrual status) are accounted for in accordance with ASC 310-30 as they display significant credit deterioration since origination.
	For pass rated loans (non-purchased credit-impaired loans), the difference between the estimated fair value of the loans (computed on a loan by loan basis) and the principal outstanding is accreted over the remaining life of the loans. We anticipate recording a provision for the acquired portfolio in future quarters related to renewing Taylor loans which will largely offset the accretion from the pass rated loans.
	In accordance with ASC 310-30, for both purchased non-impaired loans and purchased impaired loans ("PCI loans"), the difference between contractually required payments at acquisition and the cash flows expected to be collected is referred to as the non-accretable difference. Further, any excess of cash flows expected at acquisition over the estimated fair value is referred to as the accretable yield and is recognized into interest income over the remaining life of the loan when there is a reasonable expectation about the amount and timing of such cash flows.
	Substantially all of the loans acquired in transactions with the FDIC displayed at least some level of credit deterioration and as such are included as non-impaired and impaired loans as described immediately above.
	Lease investments: The Company’s investment in operating leases is reported as lease investments, net.  Rental income on operating leases is recognized as income over the lease term according to the provisions of the lease, which is generally on a straight-line basis.  The investment in equipment in operating leases is stated at cost less depreciation using the straight-line method generally over a life of five years or less.
	Premises and equipment: Premises and equipment are carried at cost less accumulated depreciation and amortization.  Depreciation and amortization is computed by the straight-line method over the estimated useful lives of the assets.  Useful lives generally range from three to seven years for computer equipment and software, five to 10 years for furniture and equipment, and five to 39 years for buildings and building improvements.  Land improvements are amortized over a period of 15 years and leasehold improvements are amortized over the term of the related lease or the estimated useful lives of the improvements, whichever is shorter.  Land is not subject to depreciation.  Maintenance and repairs are charged to expense as incurred, while major improvements are capitalized and amortized to operating expense over their identified useful lives.  Premises and equipment and other long-lived assets are tested for impairment whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable from future undiscounted cash flows.  If impaired, the assets are recorded at fair value.  Assets acquired through a business acquisition are recorded at fair value as of the acquisition date.
	Other real estate owned: Other real estate owned includes real estate assets that have been received in satisfaction of debt.  Other real estate owned is initially recorded at fair value less estimated selling costs, which establishes the cost basis.  Subsequently, other real estate owned is carried at the lower of the cost basis or fair value less estimated selling costs.  Any valuation adjustments required at the date of transfer are charged to the allowance for loan and lease losses.  Subsequently, unrealized losses and realized gains and losses on sale are included in net loss recognized on other real estate owned.
	Cash surrender value of life insurance: The Company has purchased bank-owned life insurance policies on certain executives.  Bank-owned life insurance is recorded at its cash surrender value.  Changes in the cash surrender values are included in non-interest income.
	Goodwill: The excess of the cost of an acquisition over the fair value of the net assets acquired, including core deposit and client relationship intangibles, consists of goodwill.  Under the provisions of ASC Topic 350, goodwill is subject to at least annual assessments for impairment by applying a fair value based test.  The Company reviews goodwill and other intangible assets to determine potential impairment annually, or more frequently if events and circumstances indicate that the asset might be impaired, by comparing the carrying value of the asset with the anticipated future cash flows. The Company's annual assessment is done at the unit level. As of December 31, 2014, the annual assessment date, the Company had three reporting units: banking, leasing and mortgage banking. The Company did not recognize impairment losses during the year ended December 31, 2014.
	Other intangibles: The Company’s other intangible assets consist of core deposit and customer intangibles obtained through acquisitions.  Core deposit intangibles (the portion of an acquisition purchase price which represents value assigned to the existing deposit base) have finite lives and are amortized by the declining balance method over four to 15 years.  Other intangible assets are tested for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable from future undiscounted cash flows.  If impaired, the assets are recorded at fair value.
	Mortgage Servicing Rights: The Company originates and sells residential mortgage loans in the secondary market and may retain the right to service the loans sold. Servicing involves the collection of payments from individual borrowers and the distribution of those payments to the investors. Upon a sale of mortgage loans for which servicing rights are retained, the retained mortgage servicing rights asset is capitalized at the fair value of future net cash flows expected to be realized for performing servicing activities. Purchased mortgage servicing rights are recorded at the purchase price at the date of purchase and at fair value thereafter.
	Mortgage servicing rights do not trade in an active market with readily observable prices. The Company determines the fair value of mortgage servicing rights by estimating the fair value of the future cash flows associated with the mortgage loans being serviced. Key economic assumptions used in measuring the fair value of mortgage servicing rights include, but are not limited to, prepayment speeds, discount rates, delinquencies and cost to service. The assumptions used in the valuation model are validated on a periodic basis. The fair value is validated on a quarterly basis with an independent third party.
	The Company has elected to account for mortgage servicing rights using the fair value option. Changes in the fair value are recognized in mortgage banking revenue on the Company's Consolidated Statements of Operations.
	FDIC indemnification asset: As part of the Heritage Community Bank ("Heritage"), Benchmark Bank ("Benchmark"), Broadway Bank ("Broadway"), and New Century Bank ("New Century") transactions, MB Financial Bank entered into loss-share agreements with the FDIC. These agreements cover realized losses on loans and foreclosed real estate for specified periods. See Note 5 below for more information on these agreements, including the duration of MB Financial Bank’s loss-share coverage. These loss-share assets are measured separately from the loan portfolios because they are not contractually embedded in the loans and are not transferable with the loans should MB Financial Bank choose to dispose of them. Fair values at the acquisition dates were estimated based on projected cash flows available for loss-share based on the credit adjustments estimated for each loan pool and the loss-share percentages.  The loss-share assets are also separately measured from the related loans and foreclosed real estate and recorded within other assets on the balance sheet.  The corresponding accretion is recorded in other income on the statement of operations.  Although these assets are contractual receivables from the FDIC, there are no contractual interest rates.
	When cash flow estimates are adjusted downward for a particular loan pool, the FDIC indemnification asset is increased.  An allowance for loan and lease losses is established for the impairment of the loans.  A provision for credit losses is recognized for the difference between the increase in the FDIC indemnification asset and the decrease in cash flows.
	When cash flow estimates are adjusted upward for a particular loan pool, the FDIC indemnification asset is decreased.  The difference between the decrease in the FDIC indemnification asset and the increase in cash flows is accreted over the estimated life of the loan pool.
	When cash flow estimates are adjusted downward for covered foreclosed real estate, the FDIC indemnification asset is increased.  A charge is recognized for the difference between the increase in the FDIC indemnification asset and the decrease in cash flows.
	When cash flow estimates are adjusted upward for covered foreclosed real estate, the FDIC indemnification asset is decreased.  Any write-down after the transfer to covered foreclosed real estate is reversed.
	In both scenarios, the claw-back liability for amounts owed to the FDIC for better than expected performance will increase or decrease accordingly.
	Preferred stock: Preferred stock issued in connection with the Taylor Capital Group, Inc. merger was initially recorded at fair value.  Preferred dividends declared are deducted from net income for computing income available to common stockholders and earnings per common share computations.
	Treasury stock: Treasury stock is recorded at acquisition cost. Gains and losses on disposition are recorded as increases or decreases to additional paid-in capital with losses in excess of previously recorded gains charged directly to retained earnings.
	Derivative financial instruments and hedging activities: ASC Topic 815 establishes accounting and reporting standards requiring that every derivative instrument (including certain derivative instruments embedded in other contracts) be recorded in the balance sheet as either an asset or liability measured at its fair value.  ASC Topic 815 requires that changes in the derivative’s fair value be recognized currently in earnings unless specific hedge accounting criteria are met.  Accounting for qualifying hedges allows a derivative’s gains and losses to offset related results on the hedged item in the statement of operations, and requires that a company must formally document, designate and assess the effectiveness of transactions that receive hedge accounting.
	All derivatives are recognized on the consolidated balance sheet at their fair value.  On the date the derivative contract is entered into, the Company designates the derivative as either a fair value hedge (i.e. a hedge of the fair value of a recognized asset or liability), a cash flow hedge (i.e. a hedge of the variability of cash flows to be received or paid related to a recognized asset or liability), or a non-designated derivative (i.e. an instrument with no hedging designation).  For a derivative designated as a fair value hedge, the changes in the fair value of the derivative and of the hedged item attributable to the hedged risk are recognized in earnings.  If the derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in other comprehensive income and are recognized in the statement of operations when the hedged item affects earnings.  Ineffective portions of changes in the fair value of cash flow hedges are recognized in earnings.  Changes in the fair value of derivatives that are not designated as fair value or cash flow are reported currently in earnings, as noninterest income.
The Company formally documents all relationships between hedging instruments and hedging items, as well as its risk management objective and strategy for undertaking various hedge transactions.  This process includes linking all derivatives that are designated as fair value hedges or cash flow hedges to specific assets or liabilities on the balance sheet.  The Company also formally assesses, both at the hedge’s inception and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in fair values or cash flows of hedged items.
The Company discontinues hedge accounting prospectively when it is determined that the derivative is no longer effective in offsetting changes in the fair value or cash flows of the hedged item; the derivative expires or is sold, terminated, or exercised; or management determines that designation of the derivative as a hedging instrument is no longer appropriate.  When hedge accounting is discontinued because it is determined that the derivative no longer qualifies as an effective fair value hedge, the Company continues to carry the derivative on the balance sheet at its fair value, and no longer adjusts the hedged asset or liability for changes in fair value. The adjustment of the carrying amount of the hedged asset or liability is accounted for in the same manner as other components of the carrying amount of that asset or liability.
Transfers of financial assets: Transfers of financial assets are accounted for as sales, when control over the assets has been surrendered.  Control over transferred assets is deemed to be surrendered when the assets have been isolated from the Company, the transferee obtains the right (free of conditions that constrain it from taking advantage of the right) to pledge or exchange the transferred assets, and the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Sale of maintenance contracts: LaSalle Business Solutions, LLC (LBS), a subsidiary of LaSalle Systems Leasing, Inc., sells third party maintenance contracts to customers.  The maintenance is serviced by third party providers, with LBS maintaining no legal obligation under the contract to perform additional services.  Revenues are recorded net of cost of sales, as LBS is viewed as an agent under ASC Topic 605, accepting minimal credit risk, maintaining no obligation to perform maintenance under the contracts and having no control over selection of the maintenance supplier.
Asset management and trust assets: Assets of the asset management and trust department, other than trust cash on deposit at MB Financial Bank, are not included in these consolidated financial statements because they are not assets of the bank.
Stock-based compensation: The Company accounts for its equity awards in accordance with ASC Topic 718.  ASC Topic 718 requires companies to recognize compensation expense related to equity awards in their statement of operations.  See Note 19 below for more information.
Income taxes: Deferred taxes are provided on a liability method whereby deferred tax assets are recognized for deductible temporary differences, operating loss carryforwards and tax credit carryforwards, while deferred tax liabilities are recognized for taxable temporary differences.  Temporary differences are the differences between the reported amounts of assets and liabilities and their tax bases.  Deferred tax assets are reduced by a valuation allowance when, in the opinion of management, it is more likely than not that some portion or all of the deferred tax assets will not be realized.  Deferred tax assets and liabilities are adjusted for the effects of changes in tax laws and rates on the date of enactment.
Basic and diluted earnings per common share: Earnings per common share is computed using the two-class method. Basic earnings per common share is computed by dividing net income available to common stockholders 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, though no actual shares of common stock related to restricted stock units are issued until the settlement of such units, to the extent holders of these securities receive non-forfeitable dividends or dividend equivalents at the same rate as holders of the Company's common stock. 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.
The following table presents a reconciliation of the number of shares used in the calculation of basic and diluted earnings per common share (amounts in thousands, except common share data):
		Years Ended
		December 31,
		2014		2013		2012
Distributed earnings allocated to common stock		$	34,422	$	24,290	$	7,149
Undistributed earnings		51,679		74,165		83,225
Net income		86,101		98,455		90,374
Less: preferred stock dividends and discount accretion		4,000		—		3,269
Net income available to common stockholders		82,101		98,455		87,105
Less: earnings and dividends allocated to participating securities		2		2		3
Earnings allocated to common stockholders		$	82,099	$	98,453	$	87,102
Weighted average shares outstanding for basic earnings per common share		62,012,196		54,509,612		54,270,297
Dilutive effect of equity awards		561,210		484,253		235,679
Weighted average shares outstanding for diluted earnings per common share		62,573,406		54,993,865		54,505,976
Basic earnings per common share		$	1.32	$	1.81	$	1.61
Diluted earnings per common share		1.31		1.79		1.6
Comprehensive income: Comprehensive income consists of net income and other comprehensive income.  Other comprehensive income includes unrealized gains and losses on securities available-for-sale, net of deferred taxes, which are reported as a separate component of stockholders’ equity on the consolidated balance sheet.
Segment Reporting: An operating segment is a component of an entity that: (i) engages in business activities from which it may earn revenues and incur expenses; (ii) has operating results that are reviewed regularly by the entity’s chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance; and (iii) has discrete financial information available. As of December 31, 2014, the Company had three reportable operating segments: banking, leasing and mortgage banking.
New authoritative accounting guidance:
ASC Topic 740 “Income Taxes.” New authoritative accounting guidance under ASC Topic 740, “Income Taxes” amended prior guidance to include explicit guidance on the financial statement presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. An unrecognized tax benefit, or a portion of an unrecognized tax benefit, should be presented in the financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward, except as follows. To the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position or the tax law of the applicable jurisdiction does not require the entity to use, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. The Company adopted this new authoritative guidance on January 1, 2014, and it did not have an impact on the Company's statements of operations or financial condition.
ASC Topic 310 “Receivables.” New authoritative accounting guidance under ASC Topic 310, “Receivables” amended prior guidance to clarify that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical
possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. Additionally, the amendments require interim and annual disclosures. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have a significant impact on the Company's statements of operations or financial condition.
ASC Topic 323 “Investments - Equity Method and Joint Ventures.” New authoritative accounting guidance under ASC Topic 323, “Investments - Equity Method and Joint Ventures” amended prior guidance to permit entities to make an accounting policy election to account for their investments in qualified affordable housing projects using the proportional amortization method if certain conditions are met. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the net investment performance in the statement of operation as a component of income tax expense. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have a significant impact on the Company's statements of operations or financial condition.
ASC Topics 205 “Presentation of Financial Statements” and 360 “Property, Plant, and Equipment.” New authoritative accounting guidance under ASC Topic 205, “Presentation of Financial Statements” and ASC Topic 360 “Property, Plant, and Equipment” amended prior guidance to change the requirements for reporting discontinued operations. The disposal of a component of an entity or group of components of an entity is required to be reported in discontinued operations if the disposal represents a strategic shift that has (or will have) a major effect on an entity's operations and financial results. The new authoritative guidance also requires additional disclosures about discontinued operations. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have an impact on the Company's statements of operations or financial condition.
ASC Topic 860 “Transfers and Servicing.” New authoritative accounting guidance under ASC Topic 860, “Transfers and Servicing” amended prior guidance to change the accounting for repurchase-to-maturity transactions to secured borrowing accounting and to require separate accounting for a transfer of a financial asset executed contemporaneously with a repurchase agreement with the same counterparty, which will result in secured borrowing accounting for the repurchase agreement. The new authoritative guidance also requires disclosures for a transfer of a financial asset accounted for as a sale and an agreement with the same transferee entered into in contemplation of the initial transfer that results in the transferor retaining substantially all of the exposure to the economic return on the transferred financial asset throughout the term of the transaction. The new authoritative guidance will be effective for reporting periods after January 1, 2015, and the Company is assessing the impact on the statements of operations and financial condition.
ASC Topic 718 “Compensation - Stock Compensation.” New authoritative accounting guidance under ASC Topic 718, “Compensation - Stock Compensation” amended prior guidance to require that a performance target that affects vesting and that could be achieved after the requisite service period be treated as a performance condition. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have an impact on the Company's statements of operations or financial condition.
Reclassifications: Certain prior period amounts have been reclassified to conform to current period presentation.  These reclassifications did not result in any changes to previously reported net income or stockholders’ equity.

Business_Combinations

Business Combinations	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Business Combinations	Business Combinations
	On August 18, 2014, the Company acquired Taylor Capital Group, Inc. (“Taylor Capital”), a bank holding company and the parent company of Cole Taylor Bank, a commercial bank headquartered in Chicago, through the merger (the “Merger”) of Taylor Capital with and into the Company, followed immediately by the merger of Cole Taylor Bank with and into MB Financial Bank. This transaction solidifies the Company's market position in Chicago and diversifies its revenue streams. At the effective time of the Merger (the “Effective Time”), each share of the common stock of Taylor Capital and each share of nonvoting convertible preferred stock of Taylor Capital converted into the right to receive (1) 0.64318 of a share of the common stock of the Company, and (2) $4.08 in cash. All “in-the-money” Taylor Capital stock options and warrants outstanding immediately prior to the Effective Time were canceled in exchange for the right to receive a cash payment as provided in the merger agreement, as were the outstanding unvested restricted stock awards of Taylor Capital; however, the cash consideration payable for such restricted stock awards will remain subject to vesting or other lapse restrictions. Each share of Taylor Capital’s perpetual non-cumulative preferred stock, Series A, converted into the right to receive one share of the Company’s perpetual non-cumulative preferred stock, Series A.
	The Company issued approximately 19.6 million shares of common stock and paid approximately $129.5 million in cash in the Merger. For the “in-the-money” Taylor Capital stock options and warrants, the Company paid in the aggregate approximately $4.4 million in cash. For the outstanding unvested Taylor Capital restricted stock awards, the Company will pay or has paid in the aggregate up to approximately $3.7 million in cash, as and to the extent such awards vest. The $129.5 million cash consideration includes payments for the Taylor Capital stock options, warrants and restricted stock awards.
	This business combination was accounted for under the acquisition method of accounting.  Accordingly, the results of operations of the acquired company have been included in the Company’s results of operations since the date of acquisition.  Under this method of accounting, the assets acquired, liabilities assumed and consideration paid are recorded at their estimated fair values.  The excess cost over fair value of net assets acquired is recorded as goodwill.  In the event that the fair value of net assets acquired exceeds the cost, the Company will record a gain on the acquisition. As the consideration paid for Taylor Capital exceeded the net assets acquired, goodwill of $288.2 million was recorded on the acquisition and allocated to the banking segment. Goodwill recorded in the transaction, which reflects the increased Chicago market share and related synergies expected from the combined operations, is not tax deductible. The amounts recognized for the business combination in the financial statements as of December 31, 2014 have been determined only provisionally for loans, as loan risk ratings continue to be assessed.
	Estimated fair values of the assets acquired and liabilities assumed in the Taylor Capital transaction, as of the closing date of the transaction were as follows (in thousands):
			August 18,
			2014
	ASSETS
	Cash and cash equivalents		$	154,684
	Investment securities available for sale		826,691
	Investment securities held to maturity		22,599
	Non-marketable securities - FRB and FHLB Stock		50,620
	Loans held for sale		670,671
	Loans		3,532,211
	Leases investments, net		11,885
	Premises and equipment		19,701
	Goodwill		288,152
	Core deposit intangible		20,079
	Mortgage servicing rights		224,453
	Other real estate owned		4,720
	Other assets		130,478
	Total assets		$	5,956,944
	LIABILITIES
	Deposits		$	3,953,213
	Short-term borrowings		1,035,800
	Junior subordinated notes issued to capital trusts		80,843
	Accrued expenses and other liabilities		123,028
	Total liabilities		$	5,192,884
	Series A preferred stock at $28.82 per share at August 15, 2014		$	115,280
	Total identifiable net assets less Series A preferred stock		$	648,780
	Consideration excluding Series A preferred stock:
	Market value of common stock at $26.49 per share at August 15, 2014 (19,602,482 shares of common stock issued)		$	519,270
	Cash paid		129,510
	Total fair value of consideration, excluding Series A preferred stock		$	648,780
	The Company's Series A preferred stock was valued based upon the closing price of Taylor Capital's Series A preferred stock on August 15, 2014, the last trading day before the merger date.
	Fair value estimates for loans, premises and equipment, goodwill, core deposit intangible, mortgage servicing rights, other real estate owned, other assets and total consideration have been revised compared to previously reported balances. These adjustments made during the measurement period were recorded as of the closing date of the transaction. The most significant changes were made to the fair value estimates of loans, core deposit intangibles and mortgage servicing rights as a result of additional information that was received that allowed us to refine our initial estimates. The fair value estimates of loans, core deposit intangibles and mortgage servicing rights decreased by $7.1 million, $4.9 million and $8.0 million, respectively, compared to previously reported balances.
	Purchased loans acquired in a business combination are recorded at estimated fair value on their purchase date without a carryover of the related allowance for loan and lease losses. These acquired loans are segregated into three types: pass rated loans with no discount attributable to credit quality, non-impaired loans with a discount attributable at least in part to credit quality and impaired loans with evidence of significant credit deterioration.
	•	Pass rated loans (typically performing loans) are accounted for in accordance with ASC 310-20 "Nonrefundable Fees and Other Costs" as these loans do not have evidence of credit deterioration since origination.
	•	Non-impaired loans (typically performing substandard loans) are accounted for in accordance with ASC 310-30 if they display at least some level of credit deterioration since origination.
	•	Impaired loans (typically substandard loans on non-accrual status) are accounted for in accordance with ASC 310-30 as they display significant credit deterioration since origination.
	For pass rated loans (non-purchased credit-impaired loans), the difference between the estimated fair value of the loans (computed on a loan by loan basis) and the principal outstanding is accreted over the remaining life of the loans. We anticipate recording a provision for the acquired portfolio in future quarters related to renewing Taylor Capital loans which will largely offset the accretion from the pass rated loans.
	In accordance with ASC 310-30, for both purchased non-impaired loans and purchased impaired loans ("PCI loans"), the difference between contractually required payments at acquisition and the cash flows expected to be collected is referred to as the non-accretable difference. Further, any excess of cash flows expected at acquisition over the estimated fair value is referred to as the accretable yield and is recognized into interest income over the remaining life of the loan when there is a reasonable expectation about the amount and timing of such cash flows.
	The following table presents the acquired loans as of the acquisition date (in thousands):
			PCI Loans			Non-PCI Loans
	Contractually required principal and interest payments		$	244,650		$	3,707,463
	Contractually required interest payments not expected to be collected due to estimated prepayments		—			(302,329		)
	Nonaccretable difference		(34,219		)	—
	Cash flows expected to be collected		210,431			3,405,134
	Accretable difference		(5,626		)	(77,728		)
	Fair value of acquired loans		$	204,805		$	3,327,406
	The Company incurred costs of $7.1 million and $2.4 million to directly consummate the merger for the years ended December 31, 2014 and 2013, respectively, which is recorded in professional and legal fees on the statement of operations. The Company recorded $34.8 million and $2.5 million in pre-tax merger related expenses for the years ended December 31, 2014 and 2013, respectively. The remainder of the merger related expenses primarily relate to retention and severance compensation costs and service contract termination costs. The data processing systems were converted in September 2014.
	The following table provides the unaudited pro forma information for the results of operations for the years ended December 31, 2014 and 2013, as if the acquisition had occurred January 1, 2013. The pro forma results combine the historical results of Taylor Capital into the Company's consolidated statement of income including the impact of certain purchase accounting adjustments including loan discount accretion, investment securities discount accretion, intangible assets amortization, deposit premium accretion and borrowing discount amortization. The pro forma results have been prepared for comparative purposes only and are not necessarily indicative of the results that would have been obtained had the acquisition actually occurred on January 1, 2013. No assumptions have been applied to the pro forma results of operations regarding possible revenue enhancements, provision for credit losses, expense efficiencies or asset dispositions. The merger related expenses that have been recognized are included in net income in the table below.
			For Years Ended December 31,
			2014			2013
	(in thousands)
	Total revenues (net interest income plus non-interest income)		$	774,778		$	790,655
	Net income		112,220			180,085
	Revenues and earnings of the acquired company since the acquisition date have not been disclosed as it is not practicable as Taylor Capital was merged into the Company and separate financial information is not readily available.

Restrictions_on_Cash_and_Due_F

Restrictions on Cash and Due From Banks	12 Months Ended
	Dec. 31, 2014
Restrictions on Cash and Due from Banks [Abstract]
Restrictions on Cash and Due From Banks	Restrictions on Cash and Due From Banks
	MB Financial Bank is required to maintain reserve balances in cash or on deposit with the Federal Reserve Bank, based on a percentage of deposits.  The total of those required reserve balances was approximately $127.2 million and $75.1 million at December 31, 2014 and 2013, respectively.
	The nature of the Company’s business requires that it maintain amounts with banks and federal funds sold which, at times, may exceed federally insured limits.  Management monitors these correspondent relationships and the Company has not experienced any losses in such accounts.

Investment_Securities

Investment Securities	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities
	Amortized costs and fair values of investment securities were as follows (in thousands):
		Amortized			Gross			Gross			Fair
		Cost			Unrealized			Unrealized			Value
					Gains			Losses
	December 31, 2014
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	64,612		$	1,281		$	(20	)	$	65,873
	States and political subdivisions	390,076			20,846			(68		)	410,854
	Residential mortgage-backed securities	713,413			8,977			(1,827		)	720,563
	Commercial mortgage-backed securities	186,110			1,772			(220		)	187,662
	Corporate bonds	259,526			2,428			(2,751		)	259,203
	Equity securities	10,531			66			—			10,597
		1,624,268			35,370			(4,886		)	1,654,752
	Held to Maturity
	States and political subdivisions	752,558			30,089			(382		)	782,265
	Residential mortgage-backed securities	240,822			11,974			—			252,796
		993,380			42,063			(382		)	1,035,061
	Total	$	2,617,648		$	77,433		$	(5,268	)	$	2,689,813
	December 31, 2013
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	50,486		$	1,704		$	(122	)	$	52,068
	States and political subdivisions	19,398			22			(277		)	19,143
	Residential mortgage-backed securities	696,415			8,555			(3,737		)	701,233
	Commercial mortgage-backed securities	50,891			2,050			—			52,941
	Corporate bonds	284,083			1,597			(2,610		)	283,070
	Equity securities	10,649			—			(192		)	10,457
		1,111,922			13,928			(6,938		)	1,118,912
	Held to Maturity
	States and political subdivisions	932,955			7,584			(4,366		)	936,173
	Residential mortgage-backed securities	249,578			13,178			—			262,756
		1,182,533			20,762			(4,366		)	1,198,929
	Total	$	2,294,455		$	34,690		$	(11,304	)	$	2,317,841
	The Company has no direct exposure to the State of Illinois, but approximately 27% of the state and political subdivisions portfolio consists of securities issued by municipalities located in Illinois as of December 31, 2014. Approximately 93% of such securities were general obligation issues as of December 31, 2014.
	During the third quarter of 2014, the Company repositioned its balance sheet subsequent to the Taylor Capital merger and sold certain longer-term and lower-coupon investment securities with an approximate carrying amount of $451.6 million. These investment security sales shortened the overall duration of the investment securities portfolio to pre-merger levels. Also as a part of the balance sheet repositioning, securities of states and political subdivisions with an approximate fair value of $291.2 million and amortized cost of $273.5 million were transferred from held to maturity to available for sale during the third quarter of 2014. As a result of the repositioning, the Company recognized a net loss of $3.2 million in the third quarter of 2014.
	Unrealized losses on investment securities and the fair value of the related securities at December 31, 2014 were as follows (in thousands):
		Less Than 12 Months						12 Months or More						Total
		Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
		Value			Losses			Value			Losses			Value		Losses
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	9,644		$	(20	)	$	—		$	—		$	9,644	$	(20	)
	States and political subdivisions	7,784			(21		)	3,558			(47		)	11,342		(68		)
	Residential mortgage-backed securities	235,818			(1,336		)	29,373			(491		)	265,191		(1,827		)
	Commercial mortgage-backed securities	89,509			(220		)	—			—			89,509		(220		)
	Corporate bonds	62,693			(1,159		)	9,675			(1,592		)	72,368		(2,751		)
		405,448			(2,756		)	42,606			(2,130		)	448,054		(4,886		)
	Held to Maturity
	States and political subdivisions	28,786			(130		)	14,238			(252		)	43,024		(382		)
	Totals	$	434,234		$	(2,886	)	$	56,844		$	(2,382	)	$	491,078	$	(5,268	)
	Unrealized losses on investment securities and the fair value of the related securities at December 31, 2013 were as follows (in thousands):
		Less Than 12 Months						12 Months or More						Total
		Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
		Value			Losses			Value			Losses			Value		Losses
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	18,598		$	(122	)	$	—		$	—		$	18,598	$	(122	)
	States and political subdivisions	2,275			(166		)	4,748			(111		)	7,023		(277		)
	Residential mortgage-backed securities	232,807			(2,905		)	44,182			(832		)	276,989		(3,737		)
	Corporate bonds	122,344			(2,606		)	705			(4		)	123,049		(2,610		)
	Equity securities	10,457			(192		)	—			—			10,457		(192		)
		386,481			(5,991		)	49,635			(947		)	436,116		(6,938		)
	Held to Maturity
	States and political subdivisions	235,016			(4,330		)	1,301			(36		)	236,317		(4,366		)
	Totals	$	621,497		$	(10,321	)	$	50,936		$	(983	)	$	672,433	$	(11,304	)
	The total number of security positions in the investment portfolio in an unrealized loss position at December 31, 2014 was 168 compared to 345 at December 31, 2013. Declines in the fair value of available for sale securities below their cost that are deemed to be other than temporary are reflected in earnings as realized losses to the extent the impairment is related to credit losses. The amount of the impairment related to other factors is recognized in other comprehensive income. In estimating other-than-temporary impairment losses, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, and (iii) whether or not the Company is more likely than not to sell the security before recovery of its cost basis.
As of December 31, 2014, management does not have the intent to sell any of the securities in the table above and believes that it is more likely than not that the Company will not have to sell any such securities before a recovery of cost. The fair value is expected to recover as the bonds approach their maturity date or repricing date or if market yields for such investments decline. Accordingly, as of December 31, 2014, management believes the impairments detailed in the table above are temporary.
Changes in market interest rates can significantly influence the fair value of securities, and the fair value of our municipal securities portfolio would decline substantially if interest rates increase materially.
Net (losses) gains recognized on investment securities available for sale were as follows (in thousands):
	For the Years Ended December 31,
	2014			2013			2012
Realized gains	$	2,045		$	15		$	787
Realized losses	(4,478		)	(2		)	(8		)
Impairment charges	(92		)	(14		)	(224		)
Net (losses) gains	$	(2,525	)	$	(1	)	$	555
The amortized cost and fair value of investment securities as of December 31, 2014 by contractual maturity are shown below. Maturities may differ from contractual maturities in mortgage-backed securities because the mortgages underlying the securities may be called or repaid without any penalties. Therefore, mortgage-backed securities are not included in the maturity categories in the following maturity summary.
	Amortized			Fair
(In thousands)	Cost			Value
Available for sale:
Due in one year or less	$	13,752		$	13,792
Due after one year through five years	305,172			306,103
Due after five years through ten years	39,903			40,823
Due after ten years	355,387			375,212
Equity securities	10,531			10,597
Residential and commercial mortgage-backed securities	899,523			908,225
	1,624,268			1,654,752
Held to maturity:
Due in one year or less	29,060			29,114
Due after one year through five years	247,683			249,058
Due after five years through ten years	102,901			106,556
Due after ten years	372,914			397,537
Residential mortgage-backed securities	240,822			252,796
	993,380			1,035,061
Total	$	2,617,648		$	2,689,813
Investment securities with carrying amounts of $1.5 billion and $1.2 billion at December 31, 2014 and 2013, respectively, were pledged as collateral on public deposits and for other purposes as required or permitted by law, while only $980.4 million and $908.4 million were required to be pledged at December 31, 2014 and 2013, respectively. Of those pledged, the Company had investment securities available for sale pledged as collateral for advances from the Federal Home Loan Bank of $226.9 million and $29.0 million at December 31, 2014 and 2013, respectively.

Loans

Loans	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Loans	Loans
	Loans consist of the following at (in thousands):
			December 31,
			2014				2013
	Commercial		$	3,245,206			$	1,281,377
	Commercial collateralized by assignment of lease payments		1,692,258				1,494,188
	Commercial real estate		2,544,867				1,647,700
	Residential real estate		503,287				314,440
	Construction real estate		247,068				141,253
	Indirect vehicle		268,840				262,632
	Home equity		251,909				268,289
	Other consumer		78,137				66,952
	Gross loans, excluding purchased credit-impaired and covered loans		8,831,572				5,476,831
	Purchased credit-impaired and covered loans		251,645				235,720
	Total loans		$	9,083,217			$	5,712,551
	Loans are made to individuals as well as commercial and tax exempt entities. Specific loan terms vary as to interest rate, repayment, and collateral requirements based on the type of loan requested and the credit worthiness of the prospective borrower. Except for commercial loans collateralized by assignment of lease payments and asset-based loans, credit risk tends to be geographically concentrated in that a majority of the loan customers are located in the markets serviced by MB Financial Bank.
	The Company's extension of credit is governed by its Credit Risk Policy which was established to control the quality of the Company's loans. This policy is reviewed and approved by the Company's Board of Directors on a regular basis.
	Commercial Loans. Commercial credit is extended primarily to middle market customers. Such credits are typically comprised of working capital loans, loans for physical asset expansion, asset acquisition loans and other business loans. Loans to closely held businesses will generally be guaranteed in full or for a significant amount by the businesses' principal owners. Commercial loans are made based primarily on the historical and projected cash flow of the borrower and secondarily on the underlying collateral provided by the borrower. The cash flows of borrowers, however, may not behave as forecasted and collateral securing loans may fluctuate in value due to economic or individual performance factors. Minimum standards and underwriting guidelines have been established for all commercial loan types. Asset-based loans, also included in commercial loans, are made to businesses with the primary source of repayment derived from payments on the related assets securing the loan. Collateral for these loans may include accounts receivable, inventory and equipment, and is monitored regularly to ensure ongoing sufficiency of collateral coverage and quality. The primary risk for these loans is a significant decline in collateral values due to general market conditions. Loan terms that mitigate these risks include typical industry amortization schedules, percentage of collateral advances, maintenance of cash collateral accounts and regular asset monitoring. Because of the national scope of our asset-based lending, the risk of these loans is also diversified by geography.
	Commercial Loans Collateralized by Assignment of Lease Payments ("Lease Loans"). The Company makes lease loans to lessors where the underlying leases are with both investment grade and non-investment grade companies. Investment grade lessees are companies rated in one of the four highest categories by Moody's Investor Services or Standard & Poor's Rating Services or, in the event the related lessee has not received any such rating, where the related lessee would be viewed under the underwriting policies of the Company as an investment grade company. Whether or not companies fall into this category, each lease loan is considered on its individual merit based on the financial wherewithal of the lessee using financial information available at the time of underwriting.
	Commercial Real Estate Loans. Commercial real estate loans are subject to underwriting standards and processes similar to commercial loans. These loans are viewed primarily as cash flow loans and the repayment of these loans is largely dependent on the successful operation of the property. Loan performance may be adversely affected by factors impacting the general economy or conditions specific to the real estate market such as geographic location and/or property type.
	Construction Real Estate Loans. The Company defines construction loans as loans where the loan proceeds are controlled by the Company and used exclusively for the improvement of real estate in which the Company holds a mortgage. Due to the inherent risk in this type of loan, they are subject to other industry specific policy guidelines outlined in the Company's Credit Risk Policy.
	Consumer Related Loans. The Company originates direct and indirect consumer loans, including primarily residential real estate, home equity lines and loans, credit cards, and indirect vehicle loans (motorcycle, powersports, recreational and marine vehicles). Each loan type is underwritten based upon several factors including debt to income, type of collateral and loan to collateral value, credit history and Company relationship with the borrower. Indirect loan and credit card underwriting involves the use of risk-based pricing in the underwriting process.
	Loans outstanding to executive officers and directors of the Company and MB Financial Bank, including companies in which they have management control or controlling beneficial ownership, at December 31, 2014 and 2013, were approximately $63.1 million and $24.0 million, respectively. Total advances on loans outstanding to executive officers and directors, including companies in which they have management control or controlling beneficial ownership, were $7.9 million, and total repayments were $14.9 million during the year ended December 31, 2014. Most of the increase in such loans is attributable to lending relationships held by Taylor Capital prior to its merger with the Company. In the opinion of management, these loans have similar terms to other customer loans and do not present more than normal risk of collection.
	A collateral pledge agreement exists whereby at all times, the Company must keep on hand, free of all other pledges, liens, and encumbrances, first mortgage loans and home equity loans with unpaid principal balances aggregating no less than 133% for first mortgage loans and 250% for home equity loans of the outstanding advances from the Federal Home Loan Bank.  As of December 31, 2014 and 2013, the Company had $2.0 billion and $518.4 million, respectively, of loans pledged as collateral for Federal Home Loan Bank advances.
	The following table presents the contractual aging of the recorded investment in past due loans by class of loans as of December 31, 2014 and 2013 (in thousands):
			Current				30-59 Days				60-89 Days				Loans Past Due				Total			Total
							Past Due				Past Due				90 Days or More				Past Due
	31-Dec-14
	Commercial		$	3,231,571			$	8,222			$	—			$	5,413			$	13,635		$	3,245,206
	Commercial collateralized by assignment of lease payments		1,679,991				2,025				6,095				4,147				12,267			1,692,258
	Commercial real estate:
	Healthcare		342,984				—				—				—				—			342,984
	Industrial		333,907				944				—				3,182				4,126			338,033
	Multifamily		417,504				1,377				—				1,517				2,894			420,398
	Retail		432,718				2,481				652				2,325				5,458			438,176
	Office		244,166				—				—				2,127				2,127			246,293
	Other		754,031				307				2,421				2,224				4,952			758,983
	Residential real estate		485,492				8,038				2,319				7,438				17,795			503,287
	Construction real estate		246,731				—				—				337				337			247,068
	Indirect vehicle		265,296				2,516				702				326				3,544			268,840
	Home equity		242,756				2,717				1,039				5,397				9,153			251,909
	Other consumer		78,106				16				12				3				31			78,137
	Gross loans, excluding purchased credit-impaired and covered loans		8,755,253				28,643				13,240				34,436				76,319			8,831,572
	Purchased credit-impaired and covered loans		158,215				4,432				585				88,413				93,430			251,645
	Total loans		$	8,913,468			$	33,075			$	13,825			$	122,849			$	169,749		$	9,083,217
	Non-performing loan aging		$	46,149			$	5,764			$	1,099			$	34,075			$	40,938		$	87,087
	December 31, 2013
	Commercial		$	1,273,302			$	5,952			$	626			$	1,497			$	8,075		$	1,281,377
	Commercial collateralized by assignment of lease payments		1,489,391				3,841				656				300				4,797			1,494,188
	Commercial real estate:
	Healthcare		213,665				—				—				3,064				3,064			216,729
	Industrial		372,975				5,465				—				1,404				6,869			379,844
	Multifamily		302,456				3,078				181				2,226				5,485			307,941
	Retail		334,198				328				2,816				7,258				10,402			344,600
	Office		155,936				—				—				2,066				2,066			158,002
	Other		233,464				4,898				259				1,963				7,120			240,584
	Residential real estate		302,362				1,422				1,030				9,626				12,078			314,440
	Construction real estate		138,563				391				—				2,299				2,690			141,253
	Indirect vehicle		259,488				2,210				657				277				3,144			262,632
	Home equity		257,219				1,725				2,165				7,180				11,070			268,289
	Other consumer		66,866				81				1				4				86			66,952
	Gross loans, excluding covered loans		5,399,885				29,391				8,391				39,164				76,946			5,476,831
	Covered loans		135,717				902				3,346				95,755				100,003			235,720
	Total loans		$	5,535,602			$	30,293			$	11,737			$	134,919			$	176,949		$	5,712,551
Non-performing loan aging		$	56,339			$	14,325			$	3,283			$	32,614			$	50,222		$	106,561
The following table presents the recorded investment in non-accrual loans and loans past due ninety days or more and still accruing by class of loans, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
		2014								2013
						Loans past due								Loans past due
		Non-accrual				90 days or more				Non-accrual				90 days or more
						and still accruing								and still accruing
Commercial		$	14,088			$	—			$	17,781			$	—
Commercial collateralized by assignment of lease payments		2,404				3,566				4,276				291
Commercial real estate:
Healthcare		—				—				3,064				—
Industrial		6,371				—				15,265				155
Multifamily		5,333				—				5,145				—
Office		3,644				464				11,703				—
Retail		2,986				—				2,969				—
Other		13,541				324				19,991				—
Residential real estate		17,311				—				13,009				—
Construction real estate		337				—				475				—
Indirect vehicle		1,542				—				1,459				—
Home equity		15,171				—				10,969				—
Other consumer		5				—				9				—
Total		$	82,733			$	4,354			$	106,115			$	446
The reduction in interest income associated with loans on non-accrual status was approximately $4.3 million, $4.7 million, and $5.6 million for the years ended December 31, 2014, 2013, and 2012, respectively.
The Company utilizes an internal asset classification system as a means of reporting problem and potential problem loans. Under the Company's risk rating system, the Company classifies watch list loans as “Special Mention,” “Substandard,” and “Doubtful.” Substandard loans include those characterized by the distinct possibility that the Company will sustain some loss if the deficiencies are not corrected. Loans classified as Doubtful have all the weaknesses inherent in those classified as Substandard with the added characteristic that the weaknesses present make collection or liquidation in full, on the basis of currently existing facts, conditions and values, highly questionable and improbable. Loans that do not currently expose the Company to sufficient risk to warrant classification in one of the aforementioned categories but possess weaknesses that deserve management's close attention are deemed to be Special Mention. Risk ratings are updated at least annually and any time the situation warrants.
Loans listed as not rated are included in groups of homogeneous loans with similar risk and loss characteristics and are not included in the table below. The following tables present the risk category of loans by class of loans based on the most recent analysis performed, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
		Pass				Special				Substandard				Doubtful				Total
						Mention
31-Dec-14
Commercial		$	3,036,069			$	178,984			$	30,153			$	—			$	3,245,206
Commercial collateralized by assignment of lease payments		1,680,736				6,853				4,669				—				1,692,258
Commercial real estate:
Healthcare		338,622				4,362				—				—				342,984
Industrial		314,225				8,817				14,991				—				338,033
Multifamily		412,824				920				6,654				—				420,398
Retail		423,842				2,740				11,594				—				438,176
Office		229,947				8,524				7,822				—				246,293
Other		708,447				22,013				28,523				—				758,983
Construction real estate		246,204				527				337				—				247,068
Total		$	7,390,916			$	233,740			$	104,743			$	—			$	7,729,399
December 31, 2013
Commercial		$	1,193,114			$	26,637			$	61,000			$	626			$	1,281,377
Commercial collateralized by assignment of lease payments		1,486,899				553				6,736				—				1,494,188
Commercial real estate:
Healthcare		189,705				21,186				2,774				3,064				216,729
Industrial		345,236				5,328				29,280				—				379,844
Multifamily		296,179				342				11,420				—				307,941
Retail		316,420				10,660				17,520				—				344,600
Office		151,393				2,682				3,927				—				158,002
Other		217,188				349				23,047				—				240,584
Construction real estate		139,847				540				866				—				141,253
Total		$	4,335,981			$	68,277			$	156,570			$	3,690			$	4,564,518
Special mention loans increased as of December 31, 2014 compared to December 31, 2013 primarily due to special mention loans acquired in the Taylor Capital merger. Approximately $49.1 million and $80.7 million of the substandard and doubtful loans were non-performing as of December 31, 2014 and 2013, respectively.
For residential real estate, home equity, indirect vehicle and other consumer loan classes, the Company also evaluates credit quality based on the aging status of the loan, which was previously presented, and by payment activity. The following table presents the recorded investment in those loan classes based on payment activity, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
		Performing				Non-performing				Total
31-Dec-14
Residential real estate		$	485,976			$	17,311			$	503,287
Indirect vehicle		267,297				1,543				268,840
Home equity		236,739				15,170				251,909
Other consumer		78,132				5				78,137
Total		$	1,068,144			$	34,029			$	1,102,173
December 31, 2013
Residential real estate		$	301,431			$	13,009			$	314,440
Indirect vehicle		261,173				1,459				262,632
Home equity		257,320				10,969				268,289
Other consumer		66,943				9				66,952
Total		$	886,867			$	25,446			$	912,313
Non-performing loans increased as of December 31, 2014 compared to December 31, 2013 primarily due to a group of restructured loans that were less than 90 days past due at time of migration to non-performing during the third quarter of 2014.
The following tables present loans individually evaluated for impairment by class of loans, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
		31-Dec-14
		Unpaid				Recorded				Partial				Allowance for				Average			Interest
		Principal				Investment				Charge-offs				Loan and Lease Losses				Recorded			Income
		Balance												Allocated				Investment			Recognized
With no related allowance recorded:
Commercial		$	9,752			$	8,992			$	760			$	—			$	10,324		$	—
Commercial collateralized by assignment of lease payments		2,316				2,316				—				—				2,569			121
Commercial real estate:
Healthcare		—				—				—				—				—			—
Industrial		9,115				5,858				3,257				—				7,870			—
Multifamily		1,733				1,733				—				—				1,928			52
Retail		2,025				813				1,212				—				3,465			—
Office		—				—				—				—				1,127			—
Other		1,479				1,465				14				—				5,249			—
Residential real estate		1,941				1,941				—				—				2,740			—
Construction real estate		—				—				—				—				34			—
Indirect vehicle		—				—				—				—				—			—
Home equity		577				577				—				—				762			—
Other consumer		—				—				—				—				—			—
With an allowance recorded:
Commercial		7,987				7,987				—				2,395				14,227			—
Commercial collateralized by assignment of lease payments		715				715				—				105				1,515			91
Commercial real estate:
Healthcare		—				—				—				—				—			—
Industrial		517				513				4				130				4,982			—
Multifamily		5,680				4,709				971				996				6,354			131
Retail		9,264				7,897				1,367				720				8,547			—
Office		4,528				2,986				1,542				545				2,833			—
Other		12,612				12,527				85				136				11,022			12
Residential real estate		14,234				14,234				—				3,126				14,632			—
Construction real estate		2,707				337				2,370				162				455			—
Indirect vehicle		227				227				—				14				358			—
Home equity		25,927				25,705				222				2,153				25,672			—
Other consumer		—				—				—				—				—			—
Total		$	113,336			$	101,532			$	11,804			$	10,482			$	126,665		$	407
		December 31, 2013
		Unpaid				Recorded				Partial				Allowance for				Average			Interest
		Principal				Investment				Charge-offs				Loan and Lease Losses				Recorded			Income
		Balance												Allocated				Investment			Recognized
With no related allowance recorded:
Commercial		$	8,903			$	8,903			$	—			$	—			$	8,259		$	—
Commercial collateralized by assignment of lease payments		3,401				3,401				—				—				1,030			6
Commercial real estate:
Healthcare		—				—				—				—				2,698			—
Industrial		7,560				7,560				—				—				8,900			—
Multifamily		1,166				1,166				—				—				758			11
Retail		4,466				4,466				—				—				3,628			—
Office		559				527				32				—				922			—
Other		2,963				2,963				—				—				4,380			—
Residential real estate		4,234				4,234				—				—				3,260			—
Construction real estate		—				—				—				—				—			—
Indirect vehicle		—				—				—				—				—			—
Home equity		577				577				—				—				797			—
Other consumer		—				—				—				—				—			—
With an allowance recorded:
Commercial		8,923				8,919				4				4,284				13,476			4
Commercial collateralized by assignment of lease payments		1,060				1,060				—				144				1,279			192
Commercial real estate:
Healthcare		3,186				3,064				122				382				8,189			—
Industrial		7,707				7,705				2				3,038				3,699			—
Multifamily		5,374				5,374				—				1,661				6,443			340
Retail		14,169				12,428				1,741				1,511				12,885			280
Office		2,442				2,442				—				791				4,045			—
Other		20,367				17,029				3,338				796				12,868			20
Residential real estate		13,496				12,710				786				3,119				12,966			245
Construction real estate		475				475				—				227				1,603			—
Indirect vehicle		173				123				50				57				86			—
Home equity		23,840				23,395				445				1,358				24,283			772
Other consumer		—				—				—				—				—			—
Total		$	135,041			$	128,521			$	6,520			$	17,368			$	136,454		$	1,870
Average impaired loans for the years ended December 31, 2014, 2013 and 2012 were $126.7 million, $136.5 million and $119.3 million, respectively.  Interest income recognized on impaired loans was $407 thousand, $1.9 million and $1.6 million for the years ended December 31, 2014, 2013 and 2012, respectively.
Impaired loans included accruing restructured loans of $15.6 million and $29.4 million that have been modified and are performing in accordance with those modified terms as of December 31, 2014 and 2013, respectively.  In addition, impaired loans included $25.8 million and $25.0 million of non-performing, restructured loans as of December 31, 2014 and 2013, respectively.
Loans may be restructured in an effort to maximize collections from financially distressed borrowers. We use various restructuring techniques, including, but not limited to, deferral of past due interest or principal, implementing an A/B note structure, redeeming past due taxes, reduction of interest rates, extending maturities and modification of amortization schedules. Residential real estate loans are restructured in an effort to minimize losses while allowing borrowers to remain in their primary residences when possible. Programs that we offer to residential real estate borrowers include the Home Affordable Refinance Program (“HARP”) and a restructuring program similar to the Home Affordable Modification Program (“HAMP”) for first mortgage borrowers as well as the Second Lien Modification Program (“2MP”) and similar programs for home equity borrowers in keeping with the restructuring techniques discussed above.
Occasionally, the Company will restructure a note into two separate notes (A/B structure), charging off the entire B portion of the note. The A note is structured with appropriate loan-to-value and cash flow coverage ratios that provide for a high likelihood of repayment. The A note is classified as a non-performing note until the borrower has displayed a historical payment performance for a reasonable time prior to and subsequent to the restructuring. A period of sustained repayment for at least six months generally is required to return the note to accrual status provided that management has determined that the performance is reasonably expected to continue. The A note will be classified as a restructured note (either performing or non-performing) through the calendar year of the restructuring that the historical payment performance has been established. As of December 31, 2014 and 2013, there was one A/B structure with a recorded investment of $1.0 million and $1.1 million, respectively, which is included above as an accruing restructured loans.
A loan classified as a troubled debt restructuring will no longer be included in the troubled debt restructuring disclosures in the years after the restructuring if the loan performs in accordance with the terms specified by the restructuring agreement and the interest rate specified in the restructuring agreement represents a market rate at the time of modification. The specified interest rate is considered a market rate when the interest rate is equal or greater than the rate the Company is willing to accept at the time of restructuring for a new loan with comparable risk. If there are concerns that the borrower would not be able to meet the modified terms of the loan, the loan would continue to be included in the troubled debt restructuring disclosures.
Impairment analyses on commercial-related loans classified as troubled debt restructurings are performed in conjunction with the normal allowance for loan and lease loss process. See Note 1 for additional information. Consumer loans classified as troubled debt restructurings are aggregated in two pools that share common risk characteristics, home equity and residential real estate loans, with impairment measured on a quarterly basis based on the present value of expected future cash flows discounted at the loan's effective interest rate.
The following table presents loans that have been restructured during the year ended December 31, 2014 (dollars in thousands):
		31-Dec-14
		Number of		Pre-Modification Recorded				Post-Modification Recorded				Charge-offs and
		Loans		Investment				Investment				Specific Reserves
Performing:
Residential real estate		3		$	588			$	588			$	—
Indirect vehicle		2		26				26				—
Home equity		9		2,251				2,251				—
Total		14		$	2,865			$	2,865			$	—
Non-Performing:
Commercial		1		$	263			$	263			$	85
Commercial real estate:
Multifamily		1		158				158				40
Residential real estate		6		1,850				1,850				246
Indirect vehicle		53		320				320				88
Home equity		27		3,813				3,813				335
Total		88		$	6,404			$	6,404			$	794
The following table presents loans that have been restructured during the year ended December 31, 2013 (dollars in thousands):
		December 31, 2013
		Number of			Pre-Modification Recorded				Post-Modification Recorded				Charge-offs and
		Loans			Investment				Investment				Specific Reserves
Performing:
Commercial real estate:
Multifamily		1			$	601			$	601			$	—
Residential real estate		6			910				910				—
Home equity		14			2,204				2,204				—
Total		21			$	3,715			$	3,715			$	—
Non-Performing:
Commercial		2			$	1,251			$	1,251			$	673
Commercial collateralized by assignment of lease payments		1			3,401				3,401				—
Commercial real estate:
Healthcare		1			3,164				3,164				496
Industrial		4			2,570				2,570				1,425
Multifamily		2			623				623				169
Retail		3			862				862				235
Other		1			84				84				23
Residential real estate		9			1,803				1,682				121
Indirect vehicle		26			171				129				42
Home equity		26			3,430				3,430				—
Total		75			$	17,359			$	17,196			$	3,184
Of the troubled debt restructurings entered into during the past twelve months, $188 thousand subsequently defaulted during the year ended December 31, 2014.  Performing troubled debt restructurings are considered to have defaulted when they become 90 days or more past due post-restructuring or are placed on non-accrual status.
The following tables present the troubled debt restructurings activity during the year ended December 31, 2014 (dollars in thousands):
		Performing				Non-performing
Beginning balance		$	29,430			$	24,952
Additions		2,865				6,404
Charge-offs		(451		)		(2,840		)
Principal payments, net		(2,650		)		(3,965		)
Removals		(8,574		)		(3,576		)
Transfer to other real estate owned		—				(221		)
Transfer from non-performing/performing		6,407				11,424
Transfer to non-performing/performing		(11,424		)		(6,407		)
Ending balance		$	15,603			$	25,771
Approximately $6.4 million of non-performing troubled debt restructurings were transferred to performing status. A majority of these loans were identified as non-performing troubled debt restructurings during the first half of 2013 and have performed in accordance with the modified terms. The loans continue to be reported as performing troubled debt restructurings. Loans removed from troubled debt restructuring status are those that were restructured in a previous calendar year at a market rate of interest and have performed in compliance with the modified terms.
The following table presents the type of modification for loans that have been restructured and the post-modification recorded investment during the year ended December 31, 2014 (dollars in thousands):
	December 31, 2014
	Extended				Extended Maturity				Extended
	Maturity,				and Amortization,				Maturity and				Delay in
	Amortization				Delay in Payments				Delay in Payments				Payments or
	and Reduction				and Reduction of				or Reduction of				Reduction of
	of Interest Rate				Interest Rate				Interest Rate				Interest Rate				Total
Commercial	$	—			$	—			$	263			$	—			$	263
Commercial real estate:
Multifamily	—				—				158				—				158
Residential real estate	411				—				1,268				759				2,438
Indirect vehicle	—				—				—				346				346
Home equity	2,384				878				1,211				1,591				6,064
Total	$	2,795			$	878			$	2,900			$	2,696			$	9,269
Activity in the allowance for loan and lease losses was as follows (in thousands):
		Year Ended December 31,
		2014				2013				2012
Balance at beginning of year		$	113,462			$	128,279			$	135,975
Allowance for unfunded credit commitments acquired through business combination		1,261				—				—
Utilization of allowance for unfunded credit commitments		(637		)		—				—
Provision for credit losses		12,052				(5,804		)		(8,900		)
Charge-offs:
Commercial		1,339				3,706				2,408
Commercial collateralized by assignment of lease payments		586				—				1,721
Commercial real estate		11,438				7,517				11,377
Residential real estate		1,718				2,796				2,944
Construction real estate		79				980				4,007
Indirect vehicle		3,735				2,911				2,259
Home equity		3,383				3,692				4,551
Other consumer		2,467				2,073				1,349
Total charge-offs		24,745				23,675				30,616
Recoveries:
Commercial		3,757				3,156				3,475
Commercial collateralized by assignment of lease payments		939				1,131				6,720
Commercial real estate		4,020				6,025				16,987
Residential real estate		1,190				479				501
Construction real estate		252				1,616				2,019
Indirect vehicle		1,736				1,411				1,096
Home equity		482				594				671
Other consumer		288				250				351
Total recoveries		12,664				14,662				31,820
Net charge-offs (recoveries)		12,081				9,013				(1,204		)
Allowance for credit losses		114,057				113,462				128,279
Allowance for unfunded credit commitments		(4,031		)		(1,716		)		(4,075		)
Balance at December 31,		$	110,026			$	111,746			$	124,204
The following table presents the activity in the allowance for credit losses, balance in allowance for credit losses and recorded investment in loans by portfolio segment and based on impairment method as of December 31, 2014 and 2013 (in thousands):
		Commercial				Commercial				Commercial				Residential				Construction			Indirect		Home		Other Consumer		Unfunded			Total
						collateralized  by				real estate				real estate				real estate			vehicle		equity				Commitments
						assignment of
						lease payments
December 31, 2014
Allowance for credit losses:
Beginning balance		$	23,461			$	9,159			$	51,628			$	8,872			$	6,856		$	1,662	$	8,478	$	1,630	$	1,716		$	113,462
Allowance for unfunded credit commitments acquired through business combination		—				—				—				—				—			—		—		—		1,261			1,261
Utilization of allowance for unfunded credit commitments		—				—				—				—				—			—		—		—		(637		)	(637		)
Charge-offs		1,339				586				11,438				1,718				79			3,735		3,383		2,467		—			24,745
Recoveries		3,757				939				4,020				1,190				252			1,736		482		288		—			12,664
Provision		3,692				450				(2,384		)		(1,698		)		1,889			2,024		3,879		2,509		1,691			12,052
Ending balance		$	29,571			$	9,962			$	41,826			$	6,646			$	8,918		$	1,687	$	9,456	$	1,960	$	4,031		$	114,057
Ending allowance balance attributable to loans:
Individually evaluated for impairment		$	2,395			$	105			$	2,527			$	3,126			$	162		$	14	$	2,153	$	—	$	1,348		$	11,830
Collectively evaluated for impairment		26,684				9,857				38,517				3,520				8,747			1,673		7,303		1,960		2,683			100,944
Acquired and accounted for under ASC 310-30 (1)		492				—				782				—				9			—		—		—		—			1,283
Total ending allowance balance		$	29,571			$	9,962			$	41,826			$	6,646			$	8,918		$	1,687	$	9,456	$	1,960	$	4,031		$	114,057
Loans:
Individually evaluated for impairment		$	16,979			$	3,031			$	38,501			$	16,175			$	337		$	227	$	26,282	$	—	$	—		$	101,532
Collectively evaluated for impairment		3,228,227				1,689,227				2,506,366				487,112				246,731			268,613		225,627		78,137		—			8,730,040
Acquired and accounted for under ASC 310-30 (1)		103,582				—				80,378				14,138				31,068			—		138		22,341		—			251,645
Total ending loans balance		$	3,348,788			$	1,692,258			$	2,625,245			$	517,425			$	278,136		$	268,840	$	252,047	$	100,478	$	—		$	9,083,217
December 31, 2013
Allowance for credit losses:
Beginning balance		$	24,943			$	7,755			$	61,056			$	6,941			$	11,222		$	1,324	$	9,401	$	1,562	$	4,075		$	128,279
Transfer to (from) allowance for unfunded credit commitments		—				—				—				—				500			—		—		—		(500		)	—
Charge-offs		3,706				—				7,517				2,796				980			2,911		3,692		2,073		—			23,675
Recoveries		3,156				1,131				6,025				479				1,616			1,411		594		250		—			14,662
Provision		(932		)		273				(7,936		)		4,248				(5,502		)	1,838		2,175		1,891		(1,859		)	(5,804		)
Ending balance		$	23,461			$	9,159			$	51,628			$	8,872			$	6,856		$	1,662	$	8,478	$	1,630	$	1,716		$	113,462
Ending allowance balance attributable to loans:
Individually evaluated for impairment		$	4,284			$	144			$	8,179			$	3,119			$	227		$	57	$	1,358	$	—	$	689		$	18,057
Collectively evaluated for impairment		18,693				9,015				41,763				5,753				6,567			1,605		7,120		1,630		1,027			93,173
Acquired and accounted for under ASC 310-30 (1)		484				—				1,686				—				62			—		—		—		—			2,232
Total ending allowance balance		$	23,461			$	9,159			$	51,628			$	8,872			$	6,856		$	1,662	$	8,478	$	1,630	$	1,716		$	113,462
Loans:
Individually evaluated for impairment		$	17,822			$	4,461			$	64,724			$	16,944			$	475		$	123	$	23,972	$	—	$	—		$	128,521
Collectively evaluated for impairment		1,246,523				1,489,727				1,582,976				293,883				140,778			262,509		244,317		66,952		—			5,327,665
Acquired and accounted for under ASC 310-30 (1)		35,673				—				140,504				5,448				48,313			—		107		26,320		—			256,365
Total ending loans balance		$	1,300,018			$	1,494,188			$	1,788,204			$	316,275			$	189,566		$	262,632	$	268,396	$	93,272	$	—		$	5,712,551
(1)  Loans acquired in the Taylor Capital merger and FDIC-assisted transactions and accounted for under ASC Subtopic 310-30 “Receivables — Loans and Debt Securities Acquired with Deteriorated Credit Quality.”
Purchased loans acquired in a business combination are recorded at estimated fair value on their purchase date without a carryover of the related allowance for loan and lease losses. These acquired loans are segregated into three types: pass rated loans with no discount attributable to credit quality, non-impaired loans with a discount attributable at least in part to credit quality and impaired loans with evidence of significant credit deterioration.
•	Pass rated loans (typically performing loans) are accounted for in accordance with ASC 310-20 "Nonrefundable Fees and Other Costs" as these loans do not have evidence of credit deterioration since origination.
•	Non-impaired loans (typically performing substandard loans) are accounted for in accordance with ASC 310-30 if they display at least some level of credit deterioration since origination.
•	Impaired loans (typically substandard loans on non-accrual status) are accounted for in accordance with ASC 310-30 as they display significant credit deterioration since origination.
For pass rated loans (non-purchased credit impaired loans), the difference between the estimated fair value of the loans and the principal outstanding is accreted over the remaining life of the loans. We anticipate recording a provision for the acquired portfolio in future quarters related to renewing Taylor loans which will largely offset the accretion from the pass rated loans.
In accordance with ASC 310-30, for both purchased non-impaired loans and purchased impaired loans ("PCI loans"), the difference between contractually required payments at acquisition and the cash flows expected to be collected is referred to as the non-accretable difference. Further, any excess of cash flows expected at acquisition over the estimated fair value is referred to as the accretable yield and is recognized into interest income over the remaining life of the loan when there is a reasonable expectation about the amount and timing of such cash flows.
Substantially all of the loans acquired in transactions with the FDIC displayed at least some level of credit deterioration and as such are included as non-impaired and impaired loans as described immediately above.
During the year ended December 31, 2014, there was a negative provision for credit losses of $1.3 million and net recoveries of $323 thousand, respectively, in relation to 16 pools of purchased loans with a total carrying amount of $71.7 million as of December 31, 2014. During the year ended December 31, 2013, there was a provision for credit losses of $2.5 million and net recoveries of $218 thousand in relation to 15 pools of purchased loans with a total carrying amount of $195.5 million as of December 31, 2013.  There was $1.3 million in allowance for loan and lease losses related to these purchased loans at December 31, 2014 and $2.2 million at December 31, 2013.  The provision for credit losses and accompanying charge-offs are included in the table above.
Changes in the accretable yield for loans acquired and accounted for under ASC 310-30 were as follows for the years ended December 31, 2014 and 2013 (in thousands):
		Year Ended December 31,
		2014				2013
Balance at beginning of period		$	2,337			$	5,685
Purchases		5,626				—
Accretion		(2,098		)		(4,456		)
Other		1,569				1,108
Balance at end of period		$	7,434			$	2,337
In our FDIC-assisted transactions, the fair value of purchased impaired loans, on the acquisition date, was determined based on assigned risk ratings, expected cash flows and the fair value of loan collateral. The fair value of loans that were non-impaired was determined based on estimates of losses on defaults and other market factors. Due to the loss-share agreements with the FDIC, we recorded a receivable (FDIC indemnification asset) from the FDIC equal to the present value of the corresponding reimbursement percentages on the estimated losses embedded in the loan portfolio.
When cash flow estimates are adjusted downward for a particular loan pool, the FDIC indemnification asset is increased. An allowance for loan and lease losses is established for the impairment of the loans. A provision for credit losses is recognized for the difference between the increase in the FDIC indemnification asset and the decrease in cash flows.
When cash flow estimates are adjusted upward for a particular loan pool, the FDIC indemnification asset is decreased. The difference between the decrease in the FDIC indemnification asset and the increase in cash flows is accreted over the estimated life of the loan pool.
When cash flow estimates are adjusted downward for covered foreclosed real estate, the FDIC indemnification asset is increased. A charge is recognized for the difference between the increase in the FDIC indemnification asset and the decrease in cash flows.
When cash flow estimates are adjusted upward for covered foreclosed real estate, the FDIC indemnification asset is decreased. Any write-down after the transfer to covered foreclosed real estate is reversed.
In both scenarios, the clawback liability (the amount the FDIC requires us to pay back if certain thresholds are met) will increase or decrease accordingly.
For other loans acquired through business combinations, the fair value of purchased impaired loans, on the acquisition date, was determined based on assigned risk ratings, expected cash flows and the fair value of loan collateral. The fair value of loans that were non-impaired was determined based on estimates of losses on defaults and other market factors.
The carrying amount of covered loans and other purchased non-covered loans at December 31, 2014 consisted of purchased credit-impaired loans and non-credit-impaired loans as shown in the following table (in thousands):
31-Dec-14		Purchased				Purchased  Non-Impaired				Total
		Impaired				Loans
		Loans
Covered loans:
Commercial related (1)		$	706			$	2,099			$	2,805
Commercial		830				309				1,139
Commercial real estate		20,489				16,528				37,017
Construction real estate		2,512				2,085				4,597
Other		1,877				21,622				23,499
Total covered loans		$	26,414			$	42,643			$	69,057
Estimated (payable) receivable amount from the FDIC under the loss-share agreement (2)		$	(1,850	)		$	4,513			$	2,663
Non covered loans:
Commercial related (3)		$	4,288			$	13,370			$	17,658
Commercial loans		95,350				1,681,908				1,777,258
Commercial loans collateralized by assignment of lease payments		—				160,299				160,299
Commercial real estate		43,361				926,184				969,545
Construction real estate		26,471				146,567				173,038
Other		13,118				231,921				245,039
Total non-covered loans		$	182,588			$	3,160,249			$	3,342,837
-1	Covered commercial related loans include commercial, commercial real estate and construction real estate loans acquired in connection with the Benchmark FDIC-assisted transactions.
-2	Estimated reimbursable amounts from the FDIC under the loss-share agreement exclude $303 thousand in reimbursable amounts related to covered other real estate owned.
-3	Non-covered commercial related loans include commercial, commercial real estate and construction real estate for InBank and Heritage.
Outstanding balances on purchased loans from the FDIC were $95.1 million and $273.5 million as of December 31, 2014 and 2013, respectively.  The related carrying amount on loans purchased from the FDIC was $91.4 million and $261.4 million as of December 31, 2014 and 2013, respectively.
Effective April 1, 2014, the losses on commercial related loans (commercial, commercial real estate and construction real estate) acquired in connection with the Heritage FDIC-assisted transaction ceased being covered under the loss-share agreement for that transaction. The carrying amount of those loans was $2.8 million as of December 31, 2014. Any recoveries, net of expenses, received on commercial related loans on which losses were incurred prior to April 1, 2014 will continue to be covered (and any such net recoveries must be shared with the FDIC in accordance with the loss-share agreement) through March 31, 2017. The losses on consumer related loans acquired in connection with the Heritage FDIC-assisted transaction will continue to be covered under the loss-share agreement through March 31, 2019.
The losses on commercial related loans acquired in connection with the Benchmark FDIC-assisted transaction ceased to be covered under the loss-share agreement for that transaction effective January 1, 2015. Effective July 1, 2015, the losses on commercial related loans acquired in connection with Broadway and New Century FDIC-assisted transactions will cease to be covered under the loss-share agreements for those transactions. Any recoveries, net of expenses, received on commercial related loans on which losses were incurred prior to January 1, 2015 and July 1, 2015, for the respective transactions, will continue to be covered (and any such net recoveries must be shared with the FDIC in accordance with the loss-share agreements) through December 31, 2017 and June 30, 2018 for the Benchmark FDIC-assisted transaction and Broadway and New Century FDIC-assisted transactions, respectively. The losses on consumer related loans acquired in connection with the Benchmark FDIC-assisted transaction and Broadway and New Century FDIC-assisted transactions will continue to be covered under the loss-share agreements through December 31, 2019 and June 30, 2020, respectively.

Lease_Investments

Lease Investments	12 Months Ended
	Dec. 31, 2014
Lease Investments
Lease Investments	Lease Investments
	The lease portfolio is comprised of various types of equipment, generally technology related, including computer systems and satellite equipment, material handling and general manufacturing equipment.
	Lease investments by categories follow (in thousands):
		December 31,
		2014			2013
	Direct finance leases:
	Minimum lease payments	$	340,602		$	155,945
	Estimated unguaranteed residual values	70,469			31,272
	Less: unearned income	(31,229		)	(14,473		)
	Direct finance leases (1)	$	379,842		$	172,744
	Leveraged leases:
	Minimum lease payments	$	10,689		$	24,320
	Estimated unguaranteed residual values	1,586			2,508
	Less: unearned income	(540		)	(1,644		)
	Less: related non-recourse debt	(10,330		)	(23,243		)
	Leveraged leases (1)	$	1,405		$	1,941
	Operating leases:
	Equipment, at cost	$	257,495		$	218,473
	Less accumulated depreciation	(94,662		)	(87,384		)
	Lease investments, net	$	162,833		$	131,089
	(1)Direct finance and leveraged leases are included as commercial loans collateralized by assignment of lease payments for financial
	statement purposes.
	Leases that transfer substantially all of the benefits and risk related to the equipment ownership are classified as direct finance leases. If these direct finance leases have non-recourse debt associated with them and meet the additional requirements for a leveraged lease, they are further classified as leveraged leases, and the associated debt is netted with the outstanding balance in the consolidated financial statements. Interest income on direct finance and leveraged leases is recognized using methods which approximate a level yield over the term of the lease. Operating leases are investments in equipment leased to other companies, where the residual component makes up more than 10% of the investment.  The Company funds most of the lease equipment purchases internally, but has some loans at other banks which totaled $38.5 million at December 31, 2014 and $17.5 million at December 31, 2013.
	The minimum lease payments receivable for the various categories of leases are due as follows (in thousands) for the years ending December 31,
		Direct			Leveraged			Operating
		Finance
	Year	Leases			Leases			Leases			Total
	2015	$	122,353		$	7,386		$	40,624		$	170,363
	2016	97,324			2,482			29,802			129,608
	2017	66,223			642			20,461			87,326
	2018	37,231			179			9,475			46,885
	2019	13,457			—			5,143			18,600
	Thereafter	4,014			—			3,205			7,219
		$	340,602		$	10,689		$	108,710		$	460,001
	At December 31, 2014, the following reflects the residual values for leases by category in the year the initial lease term ends (in thousands):
		Residual Values
		Direct
	End of initial lease term	Finance			Leveraged			Operating
	December 31,	Leases			Leases			Leases			Total
	2015	$	8,827		$	856		$	2,818		$	12,501
	2016	7,597			606			7,926			16,129
	2017	19,448			105			10,332			29,885
	2018	14,544			19			9,265			23,828
	2019	10,551			—			7,857			18,408
	Thereafter	9,502			—			19,050			28,552
		$	70,469		$	1,586		$	57,248		$	129,303
	The lease residual value represents the present value of the estimated fair value of the leased equipment at the termination of the lease. Lease residual values are generally reviewed quarterly, and any write-downs or charge-offs deemed necessary are recorded in the period in which they become known. To mitigate this risk of loss, we usually limit individual leased equipment residuals to approximately $1.0 million per transaction and seek to diversify both the type of equipment leased and the industries in which the lessees participate. Often times, there are several individual lease schedules under one master lease.  There were 3,793 leases at December 31, 2014 compared to 3,590 at December 31, 2013.  The average residual value per lease schedule was approximately $34 thousand at December 31, 2014 and $21 thousand at December 31, 2013.  The average residual value per master lease schedule was approximately $155 thousand at December 31, 2014 and $82 thousand at December 31, 2013.
	Income from lease financing, net was composed of (in thousands):
		Years Ended December 31,
		2014			2013			2012
	Rental income	$	64,017		$	62,629		$	49,473
	Equipment maintenance contracts revenue, net of cost of sales	16,441			11,071			14,129
	Vendor promotional income	8,382			7,587			4,051
	Other lease related revenue	2,121			1,796			167
	Gain on sale of lease payments and leased equipment, net of residual write downs	12,899			12,002			4,708
	Income on lease investments, gross	103,860			95,085			72,528
	Less: depreciation on operating leases	(39,550		)	(33,842		)	(36,146		)
	Lease financing, net	$	64,310		$	61,243		$	36,382
	Extension rents received in excess of residual values are reflected in rental income. Equipment maintenance contracts revenue represents the gross amount of revenue paid for maintenance contracts and other services brokered to customers.  The maintenance contracts are serviced by third parties, with the Company maintaining no obligation under the contracts.  The cost of sales is the amount paid by the Company to the third party maintenance provider. From time to time, the Company sells minimum lease payments to third parties.
	Gains on leased equipment periodically result when a lessee renews a lease or purchases the equipment at the end of a lease or the equipment is sold to a third party at a profit.  Individual lease transactions can, however, result in a loss.  This generally happens when, at the end of a lease, the lessee does not renew the lease or purchase the equipment.

Premises_and_Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Premises and Equipment	Premises and Equipment
	Premises and equipment consisted of (in thousands):
		December 31,
		2014			2013
	Land and land improvements	$	67,630		$	67,389
	Buildings	100,505			98,675
	Furniture and equipment	124,490			97,766
	Buildings and leasehold improvements	59,733			55,639
		352,358			319,469
	Accumulated depreciation	(113,981		)	(98,404		)
	Premises and equipment, net	$	238,377		$	221,065
	Depreciation on premises and equipment totaled $20.4 million, $18.1 million, and $16.3 million for the years ended December 31, 2014, 2013, and 2012, respectively.

Goodwill_and_Intangibles

Goodwill and Intangibles	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	Goodwill and Intangibles
	The excess of the cost of an acquisition over the fair value of the net assets acquired, including core deposit and client relationship intangibles, consists of goodwill. Under ASC Topic 350, goodwill is subject to at least annual assessments for impairment by applying a fair value based test. The Company reviews goodwill to determine potential impairment annually, or more frequently if events and circumstances indicate that goodwill might be impaired, by comparing the carrying value of the reporting units with the fair value of the reporting units.
	The Company's annual assessment date is as of December 31. Goodwill is tested for impairment at the reporting unit level. The Company had three reporting units: banking, leasing and mortgage banking. Based on the Company's 2014 goodwill impairment testing, the fair values of the three reporting units were in excess of their carrying value. No impairment losses were recognized during the years ended December 31, 2014, 2013, or 2012. The carrying amount of goodwill was $711.5 million at December 31, 2014 and $423.4 million December 31, 2013. The increase of $288.2 million in goodwill was due to the Taylor Capital merger. The carrying amount of goodwill at the banking and leasing segments was $670.9 million and $40.6 million, respectively, and none was allocated to the mortgage banking segment at December 31, 2014.
	The Company has other intangible assets consisting of core deposit and client relationship intangibles that had a remaining weighted average amortization period of approximately five years as of December 31, 2014. The Company recognized a $20.1 million core deposit intangible in 2014 due to the Taylor Capital merger, which is being amortized over 15 years using the declining balance method.
	The following table presents the changes in the carrying amount of core deposit and client relationship intangibles, gross carrying amount, accumulated amortization, and net book value as of December 31, 2014 and 2013 (in thousands):
			December 31,
			2014			2013
	Balance at beginning of period		$	23,428		$	29,512
	Amortization expense		(5,501		)	(6,084		)
	Other intangibles from business combinations		20,079			—
	Balance at end of period		$	38,006		$	23,428
	Gross carrying amount		$	80,371		$	60,292
	Accumulated amortization		(42,365		)	(36,864		)
	Net book value		$	38,006		$	23,428
	The following presents the estimated amortization expense of other intangible assets (in thousands):
	Years ending December 31,	Amount
	2015	$	5,963
	2016	5,157
	2017	4,637
	2018	4,221
	2019	2,743
	Thereafter	15,285
		$	38,006

Deposits

Deposits	12 Months Ended
	Dec. 31, 2014
Deposits [Abstract]
Deposits	Deposits
	The composition of deposits was as follows (in thousands):
			December 31,
			2014		2013
	Demand deposit accounts, noninterest bearing		$	4,118,256	$	2,375,863
	NOW and money market accounts		3,913,765		2,682,419
	Savings accounts		940,345		855,394
	Certificates of deposit, $250,000 or more		838,928		522,094
	Other certificates of deposit		1,179,648		945,489
	Total		$	10,990,942	$	7,381,259
	Certificates of deposit of $250,000 or more included $485.3 million and $224.2 million of brokered deposits at December 31, 2014 and 2013, respectively.  Brokered deposits typically consist of smaller individual time certificates that have the same liquidity characteristics and yields consistent with time certificates of $250,000 or more.
	At December 31, 2014, the scheduled maturities of certificates of deposit were as follows (in thousands):
	2015	$	1,595,106
	2016	204,649
	2017	96,043
	2018	29,585
	2019	38,858
	Thereafter	54,335
		$	2,018,576

ShortTerm_Borrowings

Short-Term Borrowings	12 Months Ended
	Dec. 31, 2014
Short-term Debt [Abstract]
Short-Term Borrowings	Short-Term Borrowings
	Short-term borrowings were as follows as of December 31, 2014 and 2013 (dollars in thousands):
		December 31,
		2014				2013
		Weighted				Weighted
		Average				Average
		Cost		Amount		Cost		Amount
	Customer repurchase agreements	0.21	%	$	219,824	0.2	%	$	193,389
	Federal Home Loan Bank advances	0.13		700,000		0.17		300,000
	Federal funds purchased	0.14		11,591		—		—
		0.15	%	$	931,415	0.18	%	$	493,389
	Securities sold under agreements to repurchase are agreements in which the Company acquires funds by selling assets to another party under a simultaneous agreement to repurchase the same assets at a specified price and date.  The Company enters into repurchase agreements and also offers a demand deposit account product to customers that sweeps their balances in excess of an agreed upon target amount into overnight repurchase agreements.  All securities sold under agreements to repurchase are recorded on the face of the balance sheet.
	The Company had fixed rate Federal Home Loan Bank ("FHLB") advances with a maturity date less than one year of $700.0 million at December 31, 2014 and $300.0 million at December 31, 2013.  At December 31, 2014, the interest rate on the advances outstanding on that date was 0.13% with maturities from January 2, 2015 to December 11, 2015. The Company has investment securities available for sale and loans pledged as collateral on these FHLB advances. See Note 4. Investment Securities and Note 5. Loans of the notes to the consolidated financial statements.
	On March 9, 2012, the Company entered into a $35.0 million unsecured line of credit with a correspondent bank. Interest is payable at a rate of one month LIBOR + 1.85%. As of December 31, 2014, no amount was outstanding and the line of credit is scheduled to mature on September 7, 2015.

Longterm_Borrowings

Long-term Borrowings	12 Months Ended
	Dec. 31, 2014
Long-term Debt, Unclassified [Abstract]
Long-term Borrowings	Long-term Borrowings
	The Company had FHLB advances with original contractual maturities greater than one year of $4.2 million and $4.3 million at December 31, 2014 and 2013, respectively. As of December 31, 2014, the advances had fixed terms with effective interest rates, net of discounts, ranging from 3.23% to 5.87% and maturities ranging from April 2021 to April 2035. The Company has investment securities available for sale and loans pledged as collateral on these FHLB advances. See Note 4. Investment Securities and Note 5. Loans of the notes to the consolidated financial statements.
	The Company had notes payable to banks totaling $38.5 million and $17.5 million at December 31, 2014 and 2013, respectively, which as of December 31, 2014, were accruing interest at rates ranging from 2.25% to 12.00%.  Lease investments include equipment with an amortized cost of $48.8 million and $25.7 million at December 31, 2014 and 2013, respectively, that is pledged as collateral on these notes.
	The Company had a $40.0 million 10-year structured repurchase agreement as of December 31, 2014 and 2013, which bears interest at a fixed rate borrowing of 4.75% and expires in 2016.
	The principal payments on long-term borrowings are due as follows (in thousands):
		Amount
	Years ending December 31,
	2015	$	17,589
	2016	53,147
	2017	6,018
	2018	1,917
	2019	680
	Thereafter	3,565
		$	82,916

Junior_Subordinated_Notes_Issu

Junior Subordinated Notes Issued to Capital Trusts	12 Months Ended
	Dec. 31, 2014
JUNIOR SUBORDINATED NOTES ISSUED TO CAPITAL TRUSTS
Junior Subordinated Notes Issued to Capital Trusts	Junior Subordinated Notes Issued to Capital Trusts
	The Company has established statutory trusts for the sole purpose of issuing trust preferred securities and related trust common securities.  The proceeds from such issuances were used by the trusts to purchase junior subordinated notes of the Company, which are the sole assets of each trust.  Concurrently with the issuance of the trust preferred securities, the Company issued guarantees for the benefit of the holders of the trust preferred securities.  The Company’s outstanding trust preferred securities qualify, and are treated by the Company, as Tier 1 regulatory capital.  The Company owns all of the common securities of each trust.  The trust preferred securities issued by each trust rank equally with the common securities in right of payment, except that if an event of default under the indenture governing the notes has occurred and is continuing, the preferred securities will rank senior to the common securities in right of payment.
	The table below summarizes the outstanding junior subordinated notes and the related trust preferred securities issued by each trust as of December 31, 2014 (in thousands):
			Coal City		MB Financial		MB Financial		MB Financial
			Capital Trust I		Capital Trust II		Capital Trust III		Capital Trust IV
	Junior Subordinated Notes:
	Principal balance		$	25,774	$	36,083	$	10,310	$	20,619
	Annual interest rate		3-mo LIBOR + 1.80%		3-mo LIBOR + 1.40%		3-mo LIBOR + 1.50%		3-mo LIBOR + 1.52%
	Stated maturity date		September 1, 2028		September 15, 2035		September 23, 2036		September 15, 2036
	Call date		September 1, 2008		December 15, 2010		September 23, 2011		September 15, 2011
	Trust Preferred Securities:
	Face Value		$	25,000	$	35,000	$	10,000	$	20,000
	Annual distribution rate		3-mo LIBOR + 1.80%		3-mo LIBOR + 1.40%		3-mo LIBOR + 1.50%		3-mo LIBOR + 1.52%
	Issuance date		July 1998		August 2005		July 2006		August 2006
	Distribution dates (1)		Quarterly		Quarterly		Quarterly		Quarterly
			MB Financial		MB Financial		FOBB		TAYC
			Capital Trust V		Capital Trust VI		Statutory Trust III (2)		Capital Trust II (3)
	Junior Subordinated Notes:
	Principal balance		$	30,928	$	23,196	$	5,155	$	41,238
	Annual interest rate		3-mo LIBOR + 1.30%		3-mo LIBOR + 1.30%		3-mo LIBOR + 2.80%		3-mo LIBOR + 2.68%
	Stated maturity date		December 15, 2037		October 30, 2037		January 23, 2034		June 17, 2034
	Call date		December 15, 2012		October 30, 2012		January 23, 2009		June 17, 2009
	Trust Preferred Securities:
	Face Value		$	30,000	$	22,500	$	5,000	$	40,000
	Annual distribution rate		3-mo LIBOR + 1.30%		3-mo LIBOR + 1.30%		3-mo LIBOR + 2.80%		3-mo LIBOR + 2.68%
	Issuance date		September 2007		October 2007		December 2003		June 2004
	Distribution dates (1)		Quarterly		Quarterly		Quarterly		Quarterly
	(1)	All distributions are cumulative and paid in cash.
	(2)	FOBB Statutory Trust III was established by First Oak Brook Bancshares, Inc. (“FOBB”) prior to the Company's acquisition of FOBB, and the junior subordinated notes issued by FOBB to FOBB Statutory Trust III were assumed by the Company upon completion of the acquisition.
	(3)	TAYC Capital Trust II was established by Taylor Capital prior to the Company's acquisition of Taylor Capital, and the junior subordinated notes issued by Taylor Capital to TAYC Capital Trust II were assumed by the Company upon completion of the acquisition. Principal balance and face value amounts associated with TAYC Capital Trust II do not include purchase accounting adjustments to such amounts, which in each case resulted in a discount of $7.5 million.
	The trust preferred securities are subject to mandatory redemption, in whole or in part, upon repayment of the junior subordinated notes at the stated maturity date or upon redemption.  Each trust’s ability to pay amounts due on the trust preferred securities is solely dependent upon the Company making payment on the related junior subordinated notes.  The Company’s obligation under the junior subordinated notes and other relevant trust agreements, in aggregate, constitute a full and unconditional guarantee by the Company of each trust’s obligations under the trust preferred securities issued by each trust.  The Company has the right to defer payment of interest on the notes and, therefore, distributions on the trust preferred securities, for up to five years, but not beyond the stated maturity date in the table above.  During any such deferral period, the Company may not pay cash dividends on its common or preferred stock and generally may not repurchase its common or preferred stock.
	On September 22, 2014, the Company redeemed the junior subordinated notes held by Taylor Capital Trust I and concurrently redeemed all of the issued and outstanding 9.75% TAYC Capital Trust I Preferred Securities. The aggregate liquidation amount of the trust preferred securities was $45.4 million. TAYC Capital Trust I was established by Taylor Capital prior to the Company's acquisition of Taylor Capital, and the junior subordinated notes issued by Taylor Capital to TAYC Capital Trust I were assumed by the Company upon completion of the acquisition. As a result, a $1.9 million gain on early extinguishment of this debt was recognized in the third quarter of 2014.

Lease_Commitments_and_Rental_E

Lease Commitments and Rental Expense	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Lease Commitments and Rental Expense	Lease Commitments and Rental Expense
	The Company leases office space for certain branch offices.  At December 31, 2014, the future minimum annual rental commitments for these noncancelable leases and subleases of such space were as follows (in thousands):
		Gross		Sublease		Net
	Years ending December 31,	Rents		Rents		Rents
	2015	$	10,272	$	797	$	9,475
	2016	8,329		484		7,845
	2017	7,398		439		6,959
	2018	5,296		414		4,882
	2019	4,680		424		4,256
	Thereafter	17,310		581		16,729
		$	53,285	$	3,139	$	50,146
	Under the terms of these leases, the Company is required to pay its pro rata share of the cost of maintenance and real estate taxes.  Certain leases also provide for increased rental payments based on increases in the Consumer Price Index.
	Net rental expense for the years ended December 31, 2014, 2013, and 2012 amounted to $7.4 million, $4.7 million, and $5.4 million, respectively.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2014
Employee Benefit Plans
Employee Benefit Plans	Employee Benefit Plans
	The Company has a defined contribution 401(k) profit sharing plan that covers most full-time employees who have completed three months of service.  Each participant under the plan may contribute up to 75% of his/her eligible compensation on a pretax basis.  The Company’s contributions consist of a discretionary profit-sharing contribution and a matching contribution of the amounts contributed by the participants.  The board of directors determines the Company’s contributions on an annual basis.
	During 2014, each participant was eligible for a maximum total Company matching contribution of 3.5% of their eligible compensation.  Additionally, the Company may make annual discretionary profit sharing contributions. The Company’s total contribution to the plan for the year ended December 31, 2014 was estimated to be $8.6 million and was $7.0 million and $6.9 million for the years ended December 31, 2013 and 2012, respectively.
	The Company has deferred compensation plans that allow certain executives, senior officers, directors and other employees to defer payment of up 100% of their base salary and bonus in the case of employees and board fees in the case of directors.  Discretionary Company contributions to these plans for the year ended December 31, 2014 were estimated to be approximately $563 thousand.  Contributions to these plans were $643 thousand and $464 thousand for the years ended December 31, 2013 and 2012, respectively.  In addition, pursuant to the Company’s agreement entered into with the Company’s Chief Executive Officer, he is entitled to receive on each December 31st while he is employed by the Company (starting December 31, 2007) a fully vested employer contribution to his account under the Company's non-stock deferred compensation plan in amount equal to 20% of his base salary then in effect.  The amounts deferred can be invested in MB Financial stock (under the Company’s stock deferred compensation plan) or publicly traded mutual funds (under the Company’s non-stock deferred compensation plan) at the discretion of the participant.  The cost of the MB Financial common stock held by MB Financial’s deferred compensation plans is reported separately in a manner similar to treasury stock (that is, changes in fair value are not recognized) with a corresponding deferred compensation obligation reflected in additional paid-in capital.  The amounts of the assets that are not invested in MB Financial common stock are recorded at their fair market value in other assets on the consolidated balance sheet.  As of December 31, 2014, the fair value of the assets held in other publicly traded funds totaled $16.8 million.  A liability is established, in other liabilities, on the consolidated balance sheet, for the fair value of the obligation to the participants.  Any increase or decrease in the fair market value of plan assets is recorded in other non-interest income on the consolidated statement of operations.  Any increase or decrease in the fair value of the deferred compensation obligation to participants is recorded as additional compensation expense or a reduction of compensation expense on the consolidated statement of operations.  The increase in fair market value of the assets and the obligation related to the deferred compensation plan was $829 thousand for the year ended December 31, 2014.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	The deferred taxes consist of (in thousands):
		December 31,
		2014			2013
	Deferred tax asset:
	Allowance for credit losses	$	43,853		$	44,418
	Federal net operating loss carryforwards	12,234			—
	State net operating loss carryforwards	26,582			24,354
	Other real estate owned	14,229			7,878
	Stock options and restricted stock	5,904			5,816
	Loans	47,668			6,833
	Deferred compensation	10,620			8,423
	Tax credit carryforwards	25,244			13,233
	Bonus accrual	5,595			4,739
	Merger and non-compete accrual	—			623
	Other items	3,390			1,222
	Total deferred tax asset	195,319			117,539
	Valuation allowance	—			—
	Total deferred tax asset, net of valuation allowance	195,319			117,539
	Deferred tax liability:
	Equipment leasing	(112,524		)	(90,941		)
	Premises and equipment	(18,817		)	(27,059		)
	Mortgage servicing rights	(64,486		)	(7		)
	Deferred income from FDIC-assisted transactions	(45,999		)	(48,272		)
	Investment securities	(1,802		)	(5,030		)
	FHLB stock dividends	(2,652		)	(2,441		)
	Core deposit intangible	(9,118		)	(2,918		)
	Other items	(2,794		)	(3,792		)
	Total deferred tax liability	(258,192		)	(180,460		)
	Net deferred tax liability	(62,873		)	(62,921		)
	Net unrealized holding gain on investment securities available for sale	(13,099		)	(5,354		)
	Net deferred tax liability	$	(75,972	)	$	(68,275	)
	The Company's federal net operating loss carryforwards totaled $35.0 million at December 31, 2014 and begin to expire in 2031 through 2034. The Company’s Illinois net operating loss carryforwards totaled $509.2 million at December 31, 2014 and begin to expire in 2021 through 2029.  In January of 2011, the State of Illinois enacted legislation suspending the utilization of net operating loss carryforwards. For Illinois purposes, no carryover deduction was allowed for any taxable year ending after December 31, 2010 and prior to December 31, 2012, and no carryover deduction could exceed $100,000 for any taxable year ending on or after December 31, 2012 and prior to December 31, 2014. Further, the legislation extended the carryover period for Illinois net operating losses by the number of taxable years in which carryover deductions are disallowed or limited.  The Company's tax credit carryforwards include federal alternative minimum tax credits of $21.4 million with an indefinite carryforward period and general business credits of $3.7 million with expiration dates occurring in 2028 through 2034. Management has determined that is more likely than not that the deferred tax assets, including the net operating loss carryforwards, as of December 31, 2014, will be realized and that no valuation allowance is required. The Company also had other state net operating loss carryforwards totaling $12.7 million at December 31, 2014, the majority of which do not begin to expire until after 2021.
	Income taxes attributable to continuing operations consist of (in thousands):
		Years Ended December 31,
		2014			2013			2012
	Current expense (benefit):
	Federal	$	25,270		$	12,234		$	15,075
	State	11,971			5,576			6,225
	Foreign	—			—			—
		37,241			17,810			21,300
	Deferred expense (benefit):
	Federal	3,122			17,245			13,688
	State	(3,170		)	4,436			1,489
	Foreign	—			—			—
		(48		)	21,681			15,177
		$	37,193		$	39,491		$	36,477
	The reconciliation between the statutory federal income tax rate of 35% and the effective tax rate on income from continuing operations follows (in thousands):
		Years Ended December 31,
		2014			2013			2012
	Federal income tax expense at expected statutory rate	$	43,153		$	48,281		$	44,398
	Increase (decrease) due to:
	Tax exempt income, net	(14,848		)	(14,200		)	(12,539		)
	State tax expense net of federal impact	5,721			6,508			5,014
	Non-deductible contingent consideration	3,738			—			—
	Non-includable increase in cash surrender value of life insurance	(1,120		)	(1,111		)	(1,177		)
	Non-deductible merger expense	988			591			—
	Adjustment of tax contingency reserves	(31		)	(24		)	14
	Other items, net	(408		)	(554		)	767
	Income tax expense	$	37,193		$	39,491		$	36,477
	ASC Topic 740, "Accounting for Uncertainty in Income Taxes" provides guidance on financial statement recognition and measurement of tax positions taken, or expected to be taken, in tax returns.
	A reconciliation of the change in unrecognized tax benefits from January 1, 2014 to December 31, 2014 is as follows (in thousands):
		Unrecognized Tax Benefit			Interest on unrecognized			Total Unrecognized Tax
		Without Interest			Tax Benefit			Benefit Including Interest
Balance at January 1, 2014	$	73		$	7		$	80
Increases for tax positions of prior years	—			6			6
Acquisition related increases	939			—			939
Benefits recognized	(31		)	(6		)	(37		)
Balance at December 31, 2014	$	981		$	7		$	988
The whole amount of unrecognized tax benefits would affect the tax provision and the effective income tax rate if recognized in future periods.  The Company elects to treat interest and penalties recognized for the underpayment of income taxes as income tax expense, to the extent not included in unrecognized tax benefits.
The Company’s federal income tax returns are open and subject to examination for the 2011 tax return year and forward.  The Company’s various state income tax returns are generally open for the 2010 tax return year and forward based on individual state statutes of limitation.  The Company is currently under examination by multiple state taxing authorities.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies
	Commitments: The Company is a party to credit-related financial instruments with off-balance-sheet risk in the normal course of business to meet the financing needs of its customers.  These financial instruments include commitments to extend credit, standby letters of credit and commercial letters of credit.  Such commitments involve, to varying degrees, elements of credit and interest rate risk in excess of the amount recognized in the consolidated balance sheets.
	The Company’s exposure to credit loss is represented by the contractual amount of these commitments.  The Company follows the same credit policies in making commitments as it does for on-balance-sheet instruments.
	At December 31, 2014 and 2013, the following financial instruments were outstanding, the contractual amounts of which represent off-balance sheet credit risk (in thousands):
		Contractual Amount
		2014		2013
	Commitments to extend credit:
	Home equity lines	$	221,102	$	208,581
	Other commitments	2,643,220		1,214,391
	Letters of credit:
	Standby	131,810		69,556
	Commercial	2,401		708
	Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract.  Commitments generally have fixed expiration dates or other termination clauses and may require a payment of a fee.  The commitments for home equity lines of credit may expire without being drawn upon.  Therefore, the total commitment amounts do not necessarily represent future cash requirements.  The amount of collateral obtained, if it is deemed necessary by the Company, is based on management’s credit evaluation of the customer.
	The Company, in the normal course of its business, regularly offers standby and commercial letters of credit to its bank customers.  Standby and commercial letters of credit are a conditional but irrevocable form of guarantee.  Under letters of credit, the Company typically guarantees payment to a third party beneficiary upon the default of payment or nonperformance by the bank customer and upon receipt of complying documentation from that beneficiary.
	Both standby and commercial letters of credit may be issued for any length of time, but normally do not exceed a period of five years.  These letters of credit may also be extended or amended from time to time depending on the bank customer’s needs.  As of December 31, 2014, the maximum remaining term for any standby letters of credit matures on September 30, 2030.  A fee is charged to the bank customer and is recognized as income over the life of the letter of credit, unless considered non-rebatable under the terms of a letter of credit application.
	At December 31, 2014, the aggregate contractual amount of these letters of credit, which represents the maximum potential amount of future payments that the Company would be obligated to pay, increased $63.9 million to $134.2 million from $70.3 million at December 31, 2013.  Of the $134.2 million in commitments outstanding at December 31, 2014, approximately $121.8 million of the letters of credit have been issued or renewed since December 31, 2013.
	Letters of credit issued on behalf of bank customers may be done on either a secured, partially secured or an unsecured basis.  If a letter credit is secured or partially secured, the collateral can take various forms including bank accounts, investments, fixed assets, inventory, accounts receivable or real estate.  The Company takes the same care in making credit decisions and obtaining collateral when it issues letters of credit on behalf of its customers as it does when making other types of loans.
	As of December 31, 2014, the Company had approximately $1.4 million in capital expenditure commitments outstanding which relate to various projects to renovate existing branches.
	Concentrations of credit risk:  The majority of the loans, commitments to extend credit and standby letters of credit have been granted to customers in the Company’s market area.  As of December 31, 2014, approximately 27% of our investments in securities issued by states and political subdivisions were within the state of Illinois.  We did not hold any direct exposure to the state of Illinois as of December 31, 2014. The distribution of commitments to extend credit approximates the distribution of loans outstanding.  Standby letters of credit are granted primarily to commercial borrowers. Our asset-based loans are made to borrowers located throughout the United States. Lease banking provides banking services to lessors located throughout the United States. Our leasing subsidiaries originate leases to companies located through the United States.
	Contingencies: In the normal course of business, the Company is involved in various legal proceedings.  In the opinion of management, any liability resulting from pending proceedings would not be expected to have a material adverse effect on the Company’s consolidated financial statements.

Regulatory_Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2014
Banking and Thrift [Abstract]
Regulatory Matters	Regulatory Matters
	The Company’s primary source of cash is dividends from its bank subsidiary.  The bank subsidiary is subject to certain restrictions on the amount of dividends that it may declare without prior regulatory approval.  In addition, the dividends declared cannot be in excess of the amount which would cause the bank subsidiary to fall below the minimum required for capital adequacy purposes.
	The Company and its bank subsidiary are subject to various regulatory capital requirements administered by the federal banking agencies.  Failure to meet minimum capital requirements can initiate certain mandatory — and additional discretionary — actions by regulators that, if undertaken, could have a direct material effect on the Company’s financial statements.  Under capital adequacy guidelines and the regulatory framework for prompt corrective action, the Company’s and its bank subsidiary’s assets, liabilities, and certain off-balance-sheet items are calculated under regulatory accounting practices.  The Company’s and its bank subsidiary’s capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings, and other factors.  Prompt corrective action provisions are not applicable to bank holding companies.
	Quantitative measures established by regulation to ensure capital adequacy require the Company and its bank subsidiary to maintain minimum amounts and ratios (set forth in the table below) of total and Tier 1 capital (as defined in the regulations) to risk-weighted assets (as defined), and of Tier 1 capital (as defined) to average assets (as defined).  Management believes the Company and its bank subsidiary met all capital adequacy requirements to which they are subject as of December 31, 2014 and 2013.
	As of December 31, 2014, the most recent regulatory notification categorized the bank subsidiary as “well capitalized” under the regulatory framework then in effect for prompt corrective action.  To be categorized as “well capitalized” as of December 31, 2014, the bank subsidiary must have maintained the total risk-based, Tier 1 risk-based, and Tier 1 leverage ratios as set forth in the well-capitalized column in the table below.  There are no conditions or events since that notification that management believes have changed the bank subsidiary’s categories.
	The required and actual amounts and ratios for the Company and its bank subsidiary are presented below as of the dates indicated (dollars in thousands):
										To Be Well
										Capitalized Under
						For Capital				Prompt Corrective
		Actual				Adequacy Purposes				Action Provisions
		Amount		Ratio		Amount		Ratio		Amount		Ratio
	As of December 31, 2014
	Total capital (to risk-weighted assets):
	Consolidated	$	1,544,759	13.62	%	$	907,369	8	%	N/A		N/A
	MB Financial Bank	1,473,928		13.03		904,917		8		$	1,131,146	10	%
	Tier 1 capital (to risk-weighted assets):
	Consolidated	1,430,702		12.61	%	453,684		4	%	N/A		N/A
	MB Financial Bank	1,359,871		12.02		452,459		4		678,688		6	%
	Tier 1 capital (to average assets):
	Consolidated	1,430,702		10.47	%	546,766		4	%	N/A		N/A
	MB Financial Bank	1,359,871		9.96		545,943		4		682,429		5	%
	As of December 31, 2013
	Total capital (to risk-weighted assets):
	Consolidated	$	1,106,541	16.53	%	$	535,430	8	%	N/A		N/A
	MB Financial Bank	974,189		14.59		534,004		8		$	667,505	10	%
	Tier 1 capital (to risk-weighted assets):
	Consolidated	1,022,512		15.28	%	267,715		4	%	N/A		N/A
	MB Financial Bank	890,380		13.34		267,002		4		400,503		6	%
	Tier 1 capital (to average assets):
	Consolidated	1,022,512		11.22	%	364,587		4	%	N/A		N/A
	MB Financial Bank	890,380		9.79		363,904		4		454,880		5	%
	N/A — not applicable

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	ASC Topic 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. A fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability. The price in the principal (or most advantageous) market used to measure the fair value of the asset or liability shall not be adjusted for transaction costs. An orderly transaction is a transaction that assumes exposure to the market for a period prior to the measurement date to allow for marketing activities that are usual and customary for transactions involving such assets and liabilities; it is not a forced transaction. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact and (iv) willing to transact.
	ASC Topic 820 requires the use of valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets and liabilities. The income approach uses valuation techniques to convert expected future amounts, such as cash flows or earnings, to a single present value amount on a discounted basis. The cost approach is based on the amount that currently would be required to replace the service capacity of an asset (replacement cost). Valuation techniques should be consistently applied. Inputs to valuation techniques refer to the assumptions that market participants would use in pricing the asset or liability. Inputs may be observable, meaning those that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources, or unobservable, meaning those that reflect the reporting entity's own assumptions about the assumptions market participants would use in pricing the asset or liability developed based on the best information available in the circumstances. In that regard, ASC Topic 820 establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows:
	Level 1: Quoted prices (unadjusted) for identical assets or liabilities in active markets that the entity has the ability to access as of the measurement date.
	Level 2: Significant other observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data.
	Level 3: Significant unobservable inputs that reflect a reporting entity's own assumptions about the assumptions that market participants would use in pricing an asset or liability.
	A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below.
	In general, fair value is based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be made to ensure that financial instruments are recorded at fair value. These adjustments may include amounts to reflect counterparty credit quality, the Company's creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time. Our valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. While management believes the Company's valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Transfers between levels of the fair value hierarchy are recognized on the actual date of the event or circumstances that caused the transfer, which generally coincides with the Company's monthly and/or quarterly valuation process.
	Financial Instruments Recorded at Fair Value on a Recurring Basis
	Securities Available for Sale. The fair values of securities available for sale are determined by quoted prices in active markets, when available, and classified as Level 1. If quoted market prices are not available, the fair value is determined by a matrix pricing, which is a mathematical technique widely used in the industry to value debt securities without relying exclusively on quoted prices for the specific securities but rather by relying on the securities' relationship to other benchmark quoted securities and classified as Level 2. In cases where significant credit valuation adjustments are incorporated into the estimation of fair value, reported amounts are classified as Level 3.
	Loans Held for Sale. Mortgage loans originated and held for sale in the secondary market are carried at fair value. The fair value of loans held for sale is determined using quoted secondary market prices and classified as level 2.
	Mortgage Servicing Rights. The Company has elected to record its mortgage servicing rights at fair value. Mortgage servicing rights do not trade in an active market with readily observable prices. Accordingly, the Company determines the fair value of mortgage servicing rights by estimating the fair value of the future cash flows associated with the mortgage loans being serviced. Key economic assumptions used in measuring the fair value of mortgage servicing rights include, but are not limited to, prepayment speeds, discount rates, delinquencies and cost to service. The assumptions used in the model are validated on a regular basis. The fair value is validated on a quarterly basis with an independent third party. Any discrepancies between the internal model and the third party validation are investigated and resolved by an internal committee. Due to the nature of the valuation inputs, mortgage servicing rights are classified in Level 3 of the fair value hierarchy.
	Assets Held in Trust for Deferred Compensation and Associated Liabilities. Assets held in trust for deferred compensation are recorded at fair value and included in “Other Assets” on the consolidated balance sheets. These assets are invested in mutual funds and classified as Level 1. Deferred compensation liabilities, also classified as Level 1, are carried at the fair value of the obligation to the employee, which corresponds to the fair value of the invested assets.
	Derivatives. Currently, we use interest rate swaps to manage our interest rate risk. The valuation of these instruments is determined using widely accepted valuation techniques including discounted cash flow analysis on the expected cash flows of each derivative and classified as Level 2. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including LIBOR rate curves. We also obtain dealer quotations for these derivatives for comparative purposes to assess the reasonableness of the model valuations. In addition, we use forward commitments to buy to-be-announced mortgage securities for which we do not intend to take delivery of the security and will enter into an offsetting position before physical delivery to lessen the price volatility of the mortgage servicing rights asset. Dealer quotations are used for these derivatives and are classified as Level 1. We also offer other derivatives, including foreign currency forward contracts and interest rate lock commitments, to our customers and offset our exposure from such contracts by purchasing other financial contracts, which are valued using market consensus prices. For certain interest rate lock commitments, the Company uses an external valuation model that relies on internally developed inputs to estimate the fair value of its interest rate lock commitments which is based on unobservable inputs that reflect management’s assumptions and specific information about each borrower transaction and is classified in Level 3 of the hierarchy.
	The following table summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2014 and 2013, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands):
			Total				Quoted Prices in				Significant Other				Significant
							Active Markets for				Observable Inputs				Unobservable Inputs
							Identical Assets				(Level 2)				(Level 3)
							(Level 1)
	2014
	Financial assets
	Securities available for sale:
	U.S. Government sponsored agencies and enterprises		$	65,873			$	—			$	65,873			$	—
	States and political subdivisions		410,854				—				410,391				463
	Residential mortgage-backed securities		720,563				—				720,053				510
	Commercial mortgage-backed securities		187,662				—				187,662				—
	Corporate bonds		259,203				—				259,203				—
	Equity securities		10,597				10,597				—				—
	Loans held for sale		737,209				—				737,209				—
	Mortgage servicing rights		235,402				—				—				235,402
	Assets held in trust for deferred compensation		16,829				16,829				—				—
	Derivative financial instruments		46,388				1,607				39,707				5,074
	Financial liabilities
	Other liabilities (1)		16,483				16,483				—				—
	Derivative financial instruments		40,499				7,209				33,290				—
	2013
	Financial assets
	Securities available for sale:
	U.S. Government sponsored agencies and enterprises		$	52,068			$	—			$	52,068			$	—
	States and political subdivisions		19,143				—				19,143				—
	Residential mortgage-backed securities		701,233				—				700,542				691
	Commercial mortgage-backed securities		52,941				—				52,941				—
	Corporate bonds		283,070				—				277,905				5,165
	Equity securities		10,457				10,457				—				—
	Loans held for sale		629				—				629				—
	Assets held in trust for deferred compensation		10,679				10,679				—				—
	Derivative financial instruments		18,645				—				18,645				—
	Financial liabilities
	Other liabilities (1)		10,569				10,569				—				—
	Derivative financial instruments		18,632				—				18,632				—
	(1) Liabilities associated with assets held in trust for deferred compensation
	The following table presents additional information about the unobservable inputs used in the fair value measurement of financial assets measured on a recurring basis that were categorized within the Level 3 of the fair value hierarchy (fair value in thousands):
		Fair Value at
		December 31, 2014				Valuation Technique		Unobservable Input		Range
		(in thousands)
	States and political subdivisions	$	463			Discounted cash flows		Credit assumption		45% Loss
	Residential mortgage-backed securities	510				Discounted cash flows		Constant pre-payment rates (CPR)		1% - 3%
	Mortgage servicing rights	235,402				Discounted cash flows		CPR		4.9% - 26.9%
								Discount rate		9.25 - 16.00
								Maturity (months)		36 - 460
								Delinquencies		0.00 - 28.57
								Costs to service		$ 60 - $ 356
	Derivative financial instruments (mortgage	5,074				Sales cash flows		Expected closing ratio		16.90% - 94.00%
	interest rate lock commitments)							Expected delivery price		98.89 bps - 110.01 bps
The significant unobservable inputs used in the fair value measurement of the Company’s mortgage servicing rights include prepayment speeds, discount rates, maturities, delinquencies and cost to service. Significant increases in prepayment speeds, discount rates, delinquencies or cost to service would result in a significantly lower fair value measurement. Conversely, significant decreases in prepayment speeds, discount rates, delinquencies or costs to service would result in a significantly higher fair value measurement. With the exception of changes in delinquencies, which can change the cost to service, the unobservable inputs move independently of each other.
Key economic assumptions used in the measuring of the fair value of the mortgage servicing rights and the sensitivity of the fair value to immediate adverse changes in those assumptions at December 31, 2014 are presented in the following table. This table does not take into account the derivatives used to economically hedge the mortgage servicing rights.
(dollars in thousands, except for weighted average cost to service)	December 31, 2014
Weighted average prepayment speed (CPR)	11.5		%
Impact on fair value of 10% adverse change	$	(9,650	)
Impact on fair value of 20% adverse change	(18,574		)
Weighted average discount rate	9.41		%
Impact on fair value of 10% adverse change	$	(8,998	)
Impact on fair value of 20% adverse change	(17,356		)
Weighted average delinquency rate	1.25		%
Impact on fair value of 10% adverse change	$	(1,520	)
Impact on fair value of 20% adverse change	(2,196		)
Weighted average costs to service	$	70
Impact on fair value of 10% adverse change	(3,325		)
Impact on fair value of 20% adverse change	(6,651		)
The Company did not have any transfers between Level 1 and Level 2 of the fair value hierarchy during the year ended December 31, 2014. The Company's policy for determining transfers between levels occurs at the end of the reporting period when circumstances in the underlying valuation criteria change and result in transfer between levels.
The following table presents additional information about financial assets measured at fair value on a recurring basis for which the Company used significant unobservable inputs (Level 3) (in thousands):
		Year Ended
		December 31,
		2014				2013				2014				2013			2014			2013
		Investment Securities								Mortgage Servicing Rights							Derivatives
Balance, beginning of period		$	5,856			$	6,071			$	—			$	—		$	—		$	—
Acquired through business combination		507				—				224,798				—			5,922			—
Purchases		—				—				1,096				—			—			—
Originations		—				—				21,285				—			—			—
Other comprehensive income		128				(44		)		(11,777		)		—			(848		)	—
Principal payments		(363		)		(157		)		—				—			—			—
Impairment charge		(92		)		(14		)		—				—			—			—
Sales		(498		)		—				—				—			—			—
Transferred out of level 3		(4,565		)		—				—				—			—			—
Balance, ending of period		$	973			$	5,856			$	235,402			$	—		$	5,074		$	—
Financial Instruments Recorded at Fair Value on a Nonrecurring Basis
The Company may be required, from time to time, to measure certain financial assets and financial liabilities at fair value on a nonrecurring basis in accordance with U.S. GAAP. These include assets that are measured at the lower of cost or fair value that were recognized at fair value below cost at the end of the period.
Impaired Loans. Loans for which it is probable that payment of interest and principal will not be made in accordance with the contractual terms of the loan agreement are considered impaired. Once a loan is identified as individually impaired, management measures impairment in accordance with ASC Topic 310. The fair value of impaired loans is estimated using one of several methods, including collateral value, market value of similar debt, enterprise value, liquidation value and discounted cash flows. Those impaired loans not requiring an allowance represent loans for which the fair value of the expected repayments or collateral exceed the recorded investments in such loans. In accordance with ASC Topic 820, impaired loans where an allowance is established based on the fair value of collateral require classification in the fair value hierarchy. Collateral values are estimated using Level 3 inputs based on customized discounting criteria. For a majority of impaired real estate loans where an allowance is established based on the fair value of collateral (90% at December 31, 2014), the Company obtains a current external appraisal. Other valuation techniques are used as well, including internal valuations, comparable property analysis and contractual sales information.
Non-Financial Assets and Non-Financial Liabilities Recorded at Fair Value
The Company has no non-financial assets or non-financial liabilities measured at fair value on a recurring basis. Certain non-financial assets and non-financial liabilities measured at fair value on a non-recurring basis include foreclosed assets and non-financial long-lived assets.
Other Real Estate and Repossessed Vehicles Owned (Foreclosed Assets). Foreclosed assets, upon initial recognition, are measured and reported at fair value through a charge-off to the allowance for loan and lease losses based upon the fair value of the foreclosed asset. The fair value of foreclosed assets, upon initial recognition, are estimated using Level 3 inputs based on customized discounting criteria.
Non-Financial Long-Lived Assets.  Non-financial long-lived assets, when determined to be impaired, are measured and reported at fair value using Level 3 inputs based on customized discounting criteria.
Assets measured at fair value on a nonrecurring basis as of December 31, 2014 and 2013 are included in the table below (in thousands):
		Total				Quoted Prices in Active				Significant Other				Significant
						Markets for Identical				Observable Inputs				Unobservable Inputs
						Assets (Level 1)				(Level 2)				(Level 3)
2014
Financial assets:
Impaired loans		$	61,717			$	—			$	—			$	61,717
Non-financial assets:
Foreclosed assets		38,619				—				—				38,619
2013
Financial assets:
Impaired loans		$	77,497			$	—			$	—			$	77,497
Non-financial assets:
Foreclosed assets		44,601				—				—				44,601
The following table presents additional information about the unobservable inputs used in the fair value measurement of financial assets measured on a nonrecurring basis that were categorized within the Level 3 of the fair value hierarchy (fair value in thousands):
	Fair Value at				Valuation
	December 31, 2014				Technique		Unobservable Input		Range
Impaired loans	$	61,717			Appraisal of collateral		Appraisal adjustments - sales costs		5% - 10%
Foreclosed assets	38,619				Appraisal of collateral		Appraisal adjustments - sales costs		5% - 10%
ASC Topic 825 requires disclosure of the fair value of financial assets and financial liabilities, including those financial assets and financial liabilities that are not measured and reported at fair value on a recurring basis or non-recurring basis. The methodologies for estimating the fair value of financial assets and financial liabilities that are measured at fair value on a recurring or non-recurring basis are discussed above. The estimated fair value approximates carrying value for cash and cash equivalents, accrued interest and the cash surrender value of life insurance policies. The methodologies for other financial assets and financial liabilities are discussed below:
The following methods and assumptions were used by the Company in estimating the fair values of its other financial instruments:
Cash and due from banks, interest earning deposits with banks and federal funds sold: The carrying amounts reported in the balance sheet approximate fair value.
Securities held to maturity: The fair values of securities held to maturity are determined by quoted prices in active markets, when available, and classified as Level 1. If quoted market prices are not available, the fair value is determined by a matrix pricing, which is a mathematical technique widely used in the industry to value debt securities without relying exclusively on quoted prices for the specific securities but rather by relying on the securities' relationship to other benchmark quoted securities and classified as Level 2. In cases where significant credit valuation adjustments are incorporated into the estimation of fair value, reported amounts are classified as Level 3.
Non-marketable securities - FHLB and FRB Stock: The carrying amounts reported in the balance sheet approximate fair value.
Loans: The fair values for loans are estimated using discounted cash flow analyses, using the corporate bond curve adjusted for liquidity for commercial loans and the swap curve adjusted for liquidity for retail loans.
Non-interest bearing deposits: The fair values disclosed are equal to their balance sheet carrying amounts, which represent the amount payable on demand.
Interest bearing deposits: The fair values disclosed for deposits with no defined maturities are equal to their carrying amounts, which represent the amounts payable on demand. Fair values for certificates of deposit are estimated using a discounted cash flow calculation that applies the Company's current incremental borrowing rates for similar terms.
Short-term borrowings: The carrying amounts of federal funds purchased, borrowings under repurchase agreements and other short-term borrowings with maturities of 90 days or less approximate their fair values.  The fair value of short-term borrowings greater than 90 days is based on the discounted value of contractual cash flows.
Long-term borrowings: The fair values of the Company's long-term borrowings (other than deposits) are estimated using discounted cash flow analyses, based on the Company's current incremental borrowing rates for similar types of borrowing arrangements.
Junior subordinated notes issued to capital trusts: The fair values of the Company's junior subordinated notes issued to capital trusts are estimated based on the quoted market prices, when available, of the related trust preferred security instruments, or are estimated based on the quoted market prices of comparable trust preferred securities.
Accrued interest: The carrying amount of accrued interest receivable and payable approximate their fair values.
Off-balance-sheet instruments: Fair values for the Company’s off-balance-sheet lending commitments (guarantees, letters of credit and commitments to extend credit) are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements.
The estimated fair values of financial instruments are as follows (in thousands):
		December 31, 2014
		Carrying Amount				Estimated Fair Value			Quoted Prices in Active			Significant Other			Significant
									Markets for Identical			Observable Inputs			Unobservable Inputs
									Assets (Level 1)			(Level 2)			(Level 3)
Financial Assets:
Cash and due from banks		$	256,804			$	256,804		$	256,804		$	—		$	—
Interest bearing deposits with banks		55,277				55,277			55,277			—			—
Investment securities available for sale		1,654,752				1,654,752			10,597			1,643,182			973
Investment securities held to maturity		993,380				1,035,061			—			1,035,061			—
Non-marketable securities - FHLB and FRB stock		75,569				75,569			—			—			75,569
Loans held for sale		737,209				737,209			—			737,209			—
Loans, net		8,973,191				8,956,494			—			—			8,956,494
Accrued interest receivable		49,065				49,065			49,065			—			—
Derivative financial instruments		46,388				46,388			1,607			39,707			5,074
Financial Liabilities:
Non-interest bearing deposits		$	4,118,256			$	4,118,256		$	4,118,256		$	—		$	—
Interest bearing deposits		6,872,686				6,877,349			—			—			6,877,349
Short-term borrowings		931,415				931,416			—			—			931,416
Long-term borrowings		82,916				86,025			—			—			86,025
Junior subordinated notes issued to capital trusts		185,778				122,408			—			—			122,408
Accrued interest payable		3,709				3,709			3,709			—			—
Derivative financial instruments		40,499				40,499			7,209			33,290			—
		December 31, 2013
		Carrying Amount				Estimated Fair Value			Quoted Prices in Active			Significant Other			Significant
									Markets for Identical			Observable Inputs			Unobservable Inputs
									Assets (Level 1)			(Level 2)			(Level 3)
Financial Assets:
Cash and due from banks		$	205,193			$	205,193		$	205,193		$	—		$	—
Interest bearing deposits with banks		268,266				268,266			268,266			—			—
Federal funds sold		42,950				42,950			42,950			—			—
Investment securities available for sale		1,118,912				1,118,912			10,457			1,102,599			5,856
Investment securities held to maturity		1,182,533				1,198,929			—			1,198,929			—
Non-marketable securities - FHLB and FRB stock		51,417				51,417			—			—			51,417
Loans held for sale		629				629			—			629			—
Loans, net		5,600,805				5,583,759			—			—			5,583,759
Accrued interest receivable		36,593				36,593			36,593			—			—
Derivative financial instruments		18,645				18,645			—			18,645			—
Financial Liabilities:
Non-interest bearing deposits		$	2,375,863			$	2,375,863		$	2,375,863		$	—		$	—
Interest bearing deposits		5,005,396				5,012,928			—			—			5,012,928
Short-term borrowings		493,389				493,384			—			—			493,384
Long-term borrowings		62,159				66,301			—			—			66,301
Junior subordinated notes issued to capital trusts		152,065				101,247			—			—			101,247
Accrued interest payable		2,042				2,042			2,042			—			—
Derivative financial instruments		18,632				18,632			—			18,632			—

Stock_Incentive_Plans

Stock Incentive Plans	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Incentive Plans	Stock Incentive Plans
	ASC Topic 718 requires that the grant date fair value of equity awards to employees be recognized as compensation expense over the period during which an employee is required to provide service in exchange for such award.
	The following table summarizes the impact of the Company’s share-based payment plans in the financial statements for the periods shown (in thousands):
		Year Ended December 31,
		2014				2013				2012
	Total cost of share-based payment plans during the year	$	8,974			$	5,456			$	4,806
	Amount of related income tax benefit recognized in income	$	3,528			$	2,159			$	1,918
	The Company adopted the Omnibus Incentive Plan (the “Omnibus Plan”) in 1997.  On May 28, 2014, the Company’s stockholders approved the third amendment and restatement of the Omnibus Plan to add 3,100,000 authorized shares for a total of 11,400,000 shares of common stock authorized to be utilized in connection with awards under the Omnibus Plan to directors, officers, and employees of the Company or any of its subsidiaries. The number of shares authorized increased by 2,400,000 to 13,800,000 upon completion of the Taylor Capital merger.  Equity grants under the Omnibus Plan can be in the form of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance units, and other stock-based awards.  Shares awarded in the form of restricted stock, restricted stock units, performance shares, performance units, or other stock-based awards generally will reduce the shares available under the Omnibus Plan on a 2-for-1 basis. Following May 28, 2014, no more than 10% of the total number of authorized shares may be issued with respect to awards granted after that date, other than stock appreciation rights, stock options and performance-based awards, which at the date of grant are not scheduled to fully vest prior to three years from the date of grant (although such awards may provide scheduled vesting earlier with respect to some of such shares and for acceleration of vesting as provided in the Omnibus Plan).  As of December 31, 2014, there were 6,243,194 shares available for future grants.
	Prior to 2014, annual equity-based incentive awards were typically granted to selected officers and employees mid-year. In 2014, these awards began being granted in the first quarter of the year.  Options are granted with an exercise price equal to no less than the market price of the Company’s shares at the date of grant; those option awards generally vest over four years of service and have 10-year contractual terms.  Restricted shares and units typically vest over a two to four year period. Equity awards may also be granted at other times throughout the year in connection with the recruitment and retention of officers and employees.  Directors currently may elect, in lieu of cash, to receive up to 70% of their fees in stock options with a five year term, which are fully vested on the grant date (provided that the director may not sell the underlying shares for at least six months after the grant date), and up to 100% of their fees in restricted shares, which vest one year after the grant date.
	The following table summarizes stock options outstanding for the year ended December 31, 2014:
		Number of			Weighted				Weighted		Aggregate
		Options			Average				Average		Intrinsic
					Exercise				Remaining		Value
					Price				Contractual		(in thousands)
									Term
									(in years)
	Options outstanding as of December 31, 2013	2,443,752			$	27.57			4.71
	Granted	231,977			29.63
	Exercised	(211,339	)		19.88
	Expired or cancelled	(177,125	)		35.78
	Forfeited	(36,551	)		22.33
	Options outstanding as of December 31, 2014	2,250,714			$	27.94			4.39		$	13,820
	Options exercisable as of December 31, 2014	1,689,055			$	29			3.2		$	9,263
	The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model based on certain assumptions.  Expected volatility is based on historical volatility and the expectations of future volatility of Company shares.  The risk free interest rate for periods within the contractual term of the option is based on the U.S. Treasury yield curve in effect at the time of the grant.  The expected life of options is estimated based on historical employee behavior and represents the period of time that options granted are expected to remain outstanding.
	The following assumptions were used for options granted during the years ended December 31, 2014, 2013, and 2012:
		For the Years Ended December 31,
		2014				2013				2012
	Risk-free interest rate	1.82		%		1.92		%		1.02		%
	Expected volatility of Company’s stock	23.16		%		25.18		%		27.17		%
	Expected dividend yield	1.65		%		1.73		%		2		%
	Expected life of options (years)	5.5				5.6				5.7
	Weighted average fair value per option of options granted during the year	$	5.93			$	5.88			$	4.23
	The total intrinsic value of options exercised during the years ended December 31, 2014, 2013, and 2012 was $2.0 million, $1.3 million, and $203 thousand, respectively.
	The following is a summary of changes in restricted shares and units for the year ended December 31, 2014:
		Number of			Weighted
		Shares			Average
					Grant Date
					Fair Value
	Shares and Units Outstanding at December 31, 2013	685,719			$	22.59
	Granted	443,375			29.23
	Vested	(305,504	)		20.53
	Forfeited	(22,505	)		24.92
	Shares and Units Outstanding at December 31, 2014	801,085			$	26.99
	The total intrinsic value of restricted shares that vested during the years ended December 31, 2014, 2013, and 2012 was $8.6 million, $5.8 million, and $6.2 million, respectively.
	The Company issued 48,569, 56,752 and 65,333 market-based restricted stock units in 2014, 2013 and 2012, respectively, which entitle recipients to shares of common stock at the end of a three year vesting period. Recipients will earn shares, totaling between 0% and 175% of the number of units issued, based on the Company's total stockholder return relative to a specified peer group of financial institutions over the three year period. The market-based restricted stock units are included in the preceding table as if the recipients earned shares equal to 100% of the units issued. A Monte Carlo simulation model was used to value the market-based restricted stock units at the time of issuance.
	The Company issued 92,717 shares of market-based restricted stock in 2011.  The market component of the vesting terms for the award requires that, for ten consecutive trading days, the closing price of the Company’s stock be at least $27.00.  The market component for this award has been satisfied and vested in full in the third quarter of 2014, on the third anniversary of the grant date. A Monte Carlo simulation model was used to value the market-based restricted stock awards at the time of issuance.
	As of December 31, 2014, there was $17.4 million of total unrecognized compensation cost related to nonvested share-based compensation arrangements (including share option and nonvested share awards) granted under the Omnibus Plan.  At December 31, 2014, the weighted-average period over which the unrecognized compensation expense is expected to be recognized was approximately 2.3 years.

Derivative_Financial_Instrumen

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments
	The Company offers various derivatives, including interest rate swaps and foreign currency forward contracts, to our customers which can mitigate our exposure to market risk through the execution of off-setting positions with inter-bank dealer counterparties. This also permits the Company to offer customized risk management solutions to our customers. These customer accommodations and any offsetting financial contracts are treated as non-designated derivative instruments and carried at fair value through an adjustment to the statement of operations.
	Interest rate swap and foreign currency forward contracts involve the risk of dealing with counterparties and their ability to meet contractual terms. The net amount payable or receivable under interest rate swaps is accrued as an adjustment to interest income.  The net amount payable for December 31, 2014 was approximately $1.1 million, and the net amount payable for December 31, 2013 was approximately $25 thousand.  The Company's credit exposure on interest rate swaps is limited to the Company's net favorable value and interest payments of all swaps to each counterparty. In such cases, collateral is generally required from the counterparties involved if the net value of the swaps exceeds a nominal amount.  At December 31, 2014, the Company’s credit exposure relating to interest rate swaps was approximately $11.2 million, which is secured by the underlying collateral on customer loans.
	The Company also enters into mortgage banking derivatives which are classified as non-designated derivatives. These derivatives include interest rate lock commitments provided to customers to fund certain mortgage loans to be sold into the secondary market and forward commitments for the future delivery of such loans. It is the Company's practice to enter into forward commitments for the future delivery of residential mortgage loans when interest rate lock commitments are entered into in order to economically hedge the effect of future changes in interest rates on its commitments to fund the loans as well as on its portfolio of mortgage loans held-for-sale.
	The Company had fair value commercial loan interest rate swaps, to hedge its interest rate risk, with an aggregate notional amount of $197 thousand at December 31, 2014.  For fair value hedges, the changes in fair values of both the hedging derivative and the hedged item were recorded in current earnings as other income.
	Interest rate swaps are used in order to lessen the price volatility of the mortgage servicing rights asset. The Company also uses forward commitments to buy to-be-announced mortgage securities for which the Company does not intend to take delivery of the security and will enter into an offsetting position before physical delivery to lessen the price volatility of the mortgage servicing rights asset. These derivatives are recorded at their fair value on the consolidated balance sheets in other assets with changes in fair value recorded on the consolidated statements of operations in mortgage banking revenue in non-interest income.
	The Company’s derivative financial instruments are summarized below as of December 31, 2014 and 2013 (in thousands):
		Asset Derivatives											Liability Derivatives
		December 31, 2014						December 31, 2013					December 31, 2014					December 31, 2013
		Notional			Estimated			Notional			Estimated		Notional		Estimated			Notional			Estimated
		Amount			Fair Value			Amount			Fair Value		Amount		Fair Value			Amount			Fair Value
	Derivative instruments designated as hedges of fair value:
	Interest rate swap contracts (1)	$	—		$	—		$	—		$	—	$	197	$	(15	)	$	238		$	(23	)
	Stand-alone derivative instruments: (2)
	Interest rate swap contracts	1,509,930			37,039			550,883			17,298		2,001,787		(30,761		)	551,798			(17,350		)
	Interest rate options contracts	55,830			283			83,907			323		55,830		(283		)	84,953			(323		)
	Foreign exchange contracts	27,402			2,276			31,361			1,006		27,002		(2,109		)	47,760			(935		)
	Spot foreign exchange contracts	512			5			—			—		304		(18		)	—			—
	Mortgage related derivatives	871,446			6,785			1,783			18		879,841		(7,313		)	250			(1		)
	Total non-hedging derivative instruments	2,465,120			46,388			667,934			18,645		2,964,764		(40,484		)	684,761			(18,609		)
	Total	$	2,465,120		$	46,388		$	667,934		$	18,645	$	2,964,961	$	(40,499	)	$	684,999		$	(18,632	)
	(1) Hedged fixed-rate commercial real estate loans
	(2) These portfolio swaps are not designated as hedging instruments under ASC Topic 815.
	Amounts included in the other income in the consolidated statements of operations related to derivative financial instruments were as follows (in thousands):
		Years Ended
		December 31,
		2014			2013			2012
	Derivative instruments designated as hedges of fair value:
	Interest rate swap contracts	$	8		$	9		$	(15	)
	Stand-alone derivative instruments:
	Interest rate swap contracts	2,458			40			30
	Interest rate options contracts	—			—			—
	Foreign exchange contracts	96			(30		)	67
	Spot foreign exchange contracts	(14		)	—			—
	Mortgage related derivatives	(965		)	(109		)	96
	Total non-hedging derivative instruments	1,575			(99		)	193
	Total	$	1,583		$	(90	)	$	178
	Methods and assumptions used by the Company in estimating the fair value of its interest rate swaps are discussed in Note 18 to consolidated financial statements.
	Certain instruments and transactions subject to an agreement similar to a master netting arrangement are eligible for offset in the consolidated balance sheet. The instruments and transactions would include derivatives, sale and repurchase agreements and reverse sale and repurchase agreements, and securities borrowing and securities lending arrangements. The Company’s derivative transactions with financial institution counterparties are generally executed under International Swaps and Derivative Association (“ISDA”) master agreements which include “right of set-off” provisions. Under these agreements, there is generally a legally enforceable right to offset recognized amounts, and there may be an intention to settle such amounts on a net basis. The Company, however, does not generally offset such financial instruments for financial reporting purposes.
	Information about the Company's financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2014 is summarized below (in thousands):
		Financial Assets									Financial Liabilities
		Gross Amount Recognized			Gross Amount Offset			Net Amount Recognized			Gross Amount Recognized		Gross Amount Offset		Net Amount Recognized
	Derivatives:
	Interest rate swaps, caps and floors	$	10,727		$	—		$	10,727		$	29,916	$	—	$	29,916
	Foreign currency forward contracts	1,525			—			1,525			709		—		709
	Mortgage banking derivatives	1,700			—			1,700			7,302		—		7,302
	Total derivatives	13,952			—			13,952			37,927		—		37,927
	Repurchase agreements	—			—			—			219,824		—		219,824
	Total	$	13,952		$	—		$	13,952		$	257,751	$	—	$	257,751
		Financial Assets											Financial Liabilities
		Net Amount Recognized			Financial Instruments			Collateral			Net Amount		Net Amount Recognized		Financial Instruments			Collateral			Net Amount
	Derivatives:
	Counterparty A	$	13		$	(13	)	$	—		$	—	$	9,556	$	(13	)	$	(9,543	)	$	—
	Counterparty B	145			(145		)	—			—		3,736		(145		)	(3,591		)	—
	Counterparty C	6,123			(6,123		)	—			—		10,335		(6,122		)	(4,213		)	—
	Other counterparties	7,671			(3,920		)	—			3,751		14,300		(3,920		)	(8,663		)	1,717
	Total derivatives	13,952			(10,201		)	—			3,751		37,927		(10,200		)	(26,010		)	1,717
	Repurchase agreements	—			—			—			—		219,824		—			(219,824		)	—
	Total	$	13,952		$	(10,201	)	$	—		$	3,751	$	257,751	$	(10,200	)	$	(245,834	)	$	1,717
	Information about the Company's financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2013 is summarized below (in thousands):
		Financial Assets									Financial Liabilities
		Gross Amount Recognized			Gross Amount Offset			Net Amount Recognized			Gross Amount Recognized		Gross Amount Offset		Net Amount Recognized
	Derivatives:
	Interest rate swaps, caps and floors	$	5,792		$	—		$	5,792		$	11,904	$	—	$	11,904
Foreign currency forward contracts	80			—			80			848		—		848
Mortgage banking derivatives	3			—			3			1		—		1
Total derivatives	5,875			—			5,875			12,753		—		12,753
Repurchase agreements	—			—			—			193,389		—		193,389
Total	$	5,875		$	—		$	5,875		$	206,142	$	—	$	206,142
	Financial Assets											Financial Liabilities
	Net Amount Recognized			Financial Instruments			Collateral			Net Amount		Net Amount Recognized		Financial Instruments			Collateral			Net Amount
Derivatives:
Counterparty A	$	883		$	(883	)	$	—		$	—	$	10,669	$	(883	)	$	(9,786	)	$	—
Counterparty B	1,836			(412		)	—			1,424		412		(412		)	—			—
Counterparty C	2,380			(1,612		)	—			768		1,612		(1,612		)	—			—
Other counterparties	776			(5		)	—			771		60		(5		)	—			55
Total derivatives	5,875			(2,912		)	—			2,963		12,753		(2,912		)	(9,786		)	55
Repurchase agreements	—			—			—			—		193,389		—			(193,389		)	—
Total	$	5,875		$	(2,912	)	$	—		$	2,963	$	206,142	$	(2,912	)	$	(203,175	)	$	55

Operating_Segments_Notes

Operating Segments (Notes)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Operating Segments	Operating Segments
	The Company's operations consist of three reportable operating segments: banking, leasing and mortgage banking. The Company offers different products and services through its three segments. The accounting policies of the segments are generally the same as those of the consolidated company.
	The banking segment generates its revenues primarily from its lending and deposit gathering activities. The profitability of this segment's operations depends primarily on its net interest income after provision for credit losses, which is the difference between interest earned on interest earning assets and interest paid on interest bearing liabilities less provision for credit losses.  The provision for credit losses is dependent on changes in its loan portfolio and management’s assessment of the collectability of the loan portfolio as well as prevailing economic and market conditions.  The banking segment is also subject to an extensive system of laws and regulations that are intended primarily for the protection of customers and depositors.  These laws and regulations govern such areas as capital, permissible activities, allowance for loan and lease losses, loans and investments, and rates of interest that can be charged on loans.
	The leasing segment generates its revenues through lease originations and related services offered through the Company's leasing subsidiaries, LaSalle Systems Leasing, Inc., Celtic Leasing Corp. and Cole Taylor Equipment Finance, LLC. The leasing subsidiaries invest directly in equipment that we lease (referred to as direct finance, leveraged or operating leases) to "Fortune 1000," large middle-market companies and healthcare providers located throughout the United States. The lease portfolio is made up of various kinds of equipment, generally technology related, such as computer systems, satellite equipment, medical equipment and general manufacturing, industrial, construction and transportation equipment. The leasing subsidiaries also specialize in selling third party equipment maintenance contracts to large companies.
	The mortgage banking segment originates mortgage loans for sale to investors and for the Company's portfolio through its retail and broker channels. This segment also services residential mortgage loans for various investors and for loans owned by the Company. The mortgage banking segment is also subject to an extensive system of laws and regulations that are intended primarily for the protection of customers.
	Net interest income for the leasing segment includes adjustments based on the Company's internal funds transfer pricing model as well as interest on loans originated for the sole purpose of funding equipment purchases related to leases at the Company's lease subsidiaries. The provision for credit losses and non-interest expense for the leasing segment includes adjustments for internal allocations of certain expenses.
	The following table presents summary financial information for the reportable segments (in thousands):
		Banking			Leasing		Mortgage Banking			Consolidated
	Year ended December 31,
	2014
	Net interest income	$	328,326		$	12,783	$	9,714		$	350,823
	Provision for credit losses	12,022			35		(5		)	12,052
	Non-interest income	115,411			59,806		46,088			221,305
	Non-interest expense (1)	350,358			39,525		46,899			436,782
	Income tax expense	21,106			12,524		3,563			37,193
	Net income	$	60,251		$	20,505	$	5,345		$	86,101
	Total assets	$	12,698,740		$	930,748	$	972,611		$	14,602,099
	Year ended December 31,
	2013
	Net interest income	$	267,131		$	5,205	$	—		$	272,336
	Provision for credit losses	(6,167		)	363		—			(5,804		)
	Non-interest income	92,936			59,794		1,664			154,394
	Non-interest expense (1)	259,753			34,835		—			294,588
	Income tax expense	28,201			11,290		—			39,491
	Net income	$	78,280		$	18,511	$	1,664		$	98,455
	Total assets	$	9,167,127		$	474,300	$	—		$	9,641,427
	Year ended December 31,
	2012
	Net interest income	$	290,881		$	1,907	$	—		$	292,788
	Provision for credit losses	(9,035		)	135		—			(8,900		)
	Non-interest income	93,124			33,744		2,325			129,193
	Non-interest expense	284,452			19,578		—			304,030
	Income tax expense	30,780			5,697		—			36,477
	Net income	$	77,808		$	10,241	$	2,325		$	90,374
	Total assets	$	9,187,480		$	384,325	$	—		$	9,571,805
	(1)	Includes merger related expenses of $34.8 million and $2.5 million in the banking segment for the years ended December 31, 2014 and 2013, respectively. Also, includes contingent consideration expense related to our acquisition of Celtic Leasing Corp. in the banking segment for the year ended December 31, 2014.

Condensed_Parent_Company_Finan

Condensed Parent Company Financial Information	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Parent Company Financial Information	Condensed Parent Company Financial Information
	The condensed financial statements of MB Financial, Inc. (parent company only) are presented below:
	Balance Sheets
	(In thousands)
		December 31,
		2014			2013
	Assets
	Cash	$	32,161		$	122,001
	Investments in subsidiaries	2,143,408			1,340,641
	Other assets	38,941			24,505
	Total assets	$	2,214,510		$	1,487,147
	Liabilities and Stockholders’ Equity
	Junior subordinated notes issued to capital trusts	$	185,778		$	152,065
	Other liabilities	446			8,400
	Stockholders’ equity	2,028,286			1,326,682
	Total liabilities and stockholders’ equity	$	2,214,510		$	1,487,147
	Statements of Operations
	(In thousands)
		Years Ended December 31,
		2014			2013			2012
	Dividends from subsidiaries	$	101,500		$	80,500		$	146,000
	Interest and other income	3,097			4,215			1,682
	Interest and other expense	14,636			7,143			7,117
	Income before income tax benefit and equity in undistributed net income of subsidiaries	89,961			77,572			140,565
	Income tax benefit	(4,590		)	(1,223		)	(2,192		)
	Income before equity in undistributed net income of subsidiaries	94,551			78,795			142,757
	Equity in undistributed net (loss) income of subsidiaries	(8,450		)	19,660			(52,383		)
	Net income	86,101			98,455			90,374
	Dividends and discount accretion on preferred shares	4,000			—			3,269
	Net income available to common stockholders	$	82,101		$	98,455		$	87,105
	Statements of Cash Flows
	(In thousands)
		Years Ended December 31,
		2014			2013			2012
	Cash Flows From Operating Activities
	Net income	$	86,101		$	98,455		$	90,374
	Adjustments to reconcile net income to net cash provided by operating activities:
	Compensation expense for share-based payment plans	8,974			5,456			4,806
	Equity in undistributed net income of subsidiaries	8,450			(19,660		)	52,383
	Change in other assets and other liabilities	(8,980		)	(1,460		)	(5,064		)
	Net cash provided by operating activities	94,545			82,791			142,499
	Cash Flows From Investing Activities
	Net decrease in loans	—			6,960			21,010
	Net cash paid in business acquisition	(101,546		)	—			—
	Net cash (used in) provided by investing activities	(101,546		)	6,960			21,010
	Cash Flows From Financing Activities
	Treasury stock transactions, net	(2,690		)	(1,672		)	(249		)
	Stock options exercised	1,034			1,014			154
	Excess tax benefits from share-based payment arrangements	396			(325		)	(390		)
	Dividends paid on common stock	(34,210		)	(24,070		)	(7,101		)
	Dividends paid on preferred stock	(2,000		)	—			(3,239		)
	Repurchase of preferred stock and warrant	—			—			(197,518		)
	Redemption of on junior subordinated notes issued to capital trusts	(45,369		)	—			(6,186		)
	Net cash used in financing activities	(82,839		)	(25,053		)	(214,529		)
	Net (decrease) increase in cash	(89,840		)	64,698			(51,020		)
	Cash:
	Beginning of year	122,001			57,303			108,323
	End of year	$	32,161		$	122,001		$	57,303

Preferred_Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Preferred Stock	Preferred Stock
	On August 18, 2014, in connection with the Taylor Capital merger, the Company issued one share of its Perpetual Non-Cumulative Preferred Stock, Series A (“Company Series A Preferred Stock”), in exchange for each of the 4,000,000 outstanding shares of Taylor Capital’s Perpetual Non-Cumulative Preferred Stock, Series A. Holders of the Company Series A Preferred Stock are entitled to receive, when as and if declared by the Company’s board of directors, non-cumulative cash dividends on the liquidation preference, which is $25 per share, at a rate of 8.00% per annum, payable quarterly. The Company Series A Preferred Stock is included in Tier 1 capital for regulatory capital purposes.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Basis of Financial Statement Presentation	Basis of Financial Statement Presentation: The consolidated financial statements include the accounts of the Company and its subsidiaries.  Significant intercompany items and transactions have been eliminated in consolidation.  The accounting and reporting policies of the Company conform to accounting principles generally accepted in the United States of America and general practices within the financial services industry.  In accordance with applicable accounting standards, the Company does not consolidate statutory trusts established for the sole purpose of issuing trust preferred securities and related trust common securities.  See Note 12 below for more detail.  In preparing the financial statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and revenues and expenses for the year.  Actual results could differ from those estimates.  Areas involving the use of management’s estimates and assumptions, which are more susceptible to change in the near term include the allowance for loan and lease losses; residual value of direct finance, leveraged, and operating leases; valuation of mortgage servicing rights; income tax accounting; fair value measurements for assets and liabilities; and goodwill.
Cash and cash equivalents	Cash and cash equivalents: For purposes of reporting cash flows, cash and cash equivalents includes cash on hand, amounts due from banks (including cash items in process of clearing), interest-bearing deposits with banks, with original maturities of 90 days or less.
Investment securities	Investment securities: Securities classified as available for sale are those securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity.  Any decision to sell a security classified as available for sale is based on various factors, including movements in interest rates, changes in the maturity mix of assets and liabilities, liquidity needs, regulatory capital considerations, and other factors.  Securities available for sale are reported at fair value with unrealized gains or losses reported as accumulated other comprehensive income, net of the related deferred tax effect.  Securities classified as held to maturity are those securities that the Company intends to hold until maturity and are reported at amortized cost.
	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 level-yield method.  In determining the estimated life of a mortgage-related security, certain judgments are required as to the timing and amount of future principal prepayments.  These judgments are made based upon the actual performance of the underlying security and the general market consensus regarding changes in mortgage interest rates and underlying prepayment estimates.  Amortization of premium and accretion of discount is included in interest income from the related security.  Realized gains or losses, determined on the basis of the cost of specific securities sold, are included in earnings.
	The Company evaluates the portfolio for impairment each quarter.  In estimating other-than-temporary losses, the Company considers the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer, and whether the Company is more likely than not to sell the security before recovery of its cost basis.  If the Company intends to sell an impaired security, the Company records an other-than-temporary loss in an amount equal to the entire difference between the fair value and amortized cost.  If a security is determined to be other-than-temporarily impaired, but the Company does not intend to sell the security, only the credit portion of the estimated loss is recognized in earnings, with the other portion of the loss recognized in other comprehensive income.
Federal Home Loan Bank and Federal Reserve Bank stock	Federal Home Loan Bank and Federal Reserve Bank stock: The Company owns investments in the stock of the Federal Reserve Bank of Chicago (“FRB”) and the Federal Home Loan Bank of Chicago (“FHLB”). No ready market exists for these stocks, and they have no quoted market values. The Bank, as a member of the Federal Reserve System and the FHLB, is required to maintain an investment in the capital stock of the FRB and FHLB. The stock is redeemable at par by the FRB and FHLB, respectively, and is, therefore, carried at cost and periodically evaluated for impairment.
Loans held for sale	Loans held for sale: Mortgage loans originated and intended for sale in the secondary market are reflected at fair value.  Changes in the fair value are recognized in mortgage banking revenue on the Company's Consolidated Statements of Operations.
Mortgage Loan Representation and Warranty Reserve	Mortgage Loan Representation and Warranty Reserve: The Company originates and sells residential mortgage loans in the secondary market. When the Company sells mortgage loans, it makes customary representations and warranties to the purchasers about various characteristics of each loan, such as the ownership of the loan, the validity of the lien securing the loan, the nature and extent of underwriting standards applied and the types of documentation being provided. These representations and warranties are generally enforceable over the life of the loan. If a defect in the origination process is identified, the Company may be required to either repurchase the loan or indemnify the purchaser for losses it sustains on the loan. If there are no such defects, the Company has no liability to the purchaser for losses it may incur on such loans.
	The Company maintains a representation and warranty reserve to account for the expected losses related to loans it might be required to repurchase or the indemnity payments it may have to make to purchasers. The representation and warranty reserve reflects management's best estimate of probable lifetime loss. The reserve considers both the estimate of expected losses on loans sold during the current accounting period as well as adjustments to the Company's previous estimate of expected losses on loans sold. Factors considered include borrower performance, repurchase demand behavior, and historical loan defect experience. Management monitors the adequacy of the overall reserve and makes adjustments to the level of reserve, as necessary, after consideration of other qualitative factors.
	At the time a loan is funded, the representation and warranty reserve is recorded as a decrease in mortgage banking revenue on the Consolidated Statements of Operations and recorded in accrued interest, taxes and other liabilities on the Company's Consolidated Balance Sheets. Changes to the reserve are recorded as an increase or decrease to mortgage banking revenue on the Consolidated Statements of Operations.
Loans and leases	Loans and leases: Loans are stated at the amount of unpaid principal reduced by the allowance for loan and lease losses and unearned income.  Direct finance and leveraged leases are included as lease loans for financial statement purposes.  Direct finance leases are stated as the sum of remaining minimum lease payments from lessees plus estimated residual values less unearned lease income.  Leveraged leases are stated at the sum of remaining minimum lease payments from lessees (less nonrecourse debt payments) plus estimated residual values less unearned lease income.  On a quarterly basis, management reviews the lease residuals for potential impairment.  Unearned lease income on direct finance and leveraged leases is recognized over the lives of the leases using the level-yield method.
	Loan origination and commitment fees and certain direct loan origination costs are deferred and the net amount amortized as an adjustment of the related loan’s yield.  The Company is amortizing these amounts over the contractual life of the loan.  Commitment fees based upon a percentage of a customer’s unused line of credit and fees related to standby letters of credit are recognized over the commitment period.
	Interest income is accrued daily on the Company’s outstanding loan balances.  The accrual of interest on loans is discontinued at the time the loan is 90 days past due unless the credit is well-secured and in process of renewal or collection.  Past due status is based on contractual terms of the loan.  In all cases, loans are placed on non-accrual or charged-off at an earlier date if collection of principal or interest is considered doubtful.  All interest accrued but not collected for loans that are placed on non-accrual or charged-off is reversed against interest income.
	For impaired loans, accrual of interest is discontinued on a loan when management believes, after considering collection efforts and other factors, the borrower’s financial condition is such that collection of interest is doubtful.  Cash collections on impaired loans are generally credited to the loan balance, and no interest income is recognized on those loans until the principal balance has been determined to be collectible.  Loans, other than those included in large groups of smaller-balance homogeneous loans, are considered impaired when it is probable the Company will be unable to collect all contractual principal and interest payments due in accordance with the terms of the loan agreement.  Impaired loans include non-accrual loans and loans classified as a troubled debt restructuring. Impaired loans are measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate or, as a practical expedient, based on the loan’s observable market price or the fair value of the collateral if the loan is collateral dependent.  The amount of impairment, if any and any subsequent changes are charged against the allowance for loan and lease losses.
Troubled debt restructurings	Troubled debt restructurings:  A loan is classified as a troubled debt restructuring when a borrower is experiencing financial difficulties that leads to a restructuring of the loan, and the Company grants concessions to the borrower in the restructuring that it would not otherwise consider. These concessions may include rate reductions, principal forgiveness, deferral of past due interest or principal, extension of maturity date, modification of amortization schedules, redemption of past due taxes and other actions intended to minimize potential losses.
	In determining whether a debtor is experiencing financial difficulties, the Company considers if the debtor is in payment default or would be in payment default in the foreseeable future without the modification, the debtor declared or is in the process of declaring bankruptcy, there is substantial doubt that the debtor will continue as a going concern, the debtor has securities that have been or are in the process of being delisted, the debtor’s entity-specific projected cash flows will not be sufficient to service any of its debt, or the debtor cannot obtain funds from sources other than the existing creditors at a market rate for debt with similar risk characteristics.
	In determining whether the Company has granted a concession, the Company assesses, if it does not expect to collect all amounts due, whether the current value of the collateral will satisfy the amounts owed, whether additional collateral or guarantees from the debtor will serve as adequate compensation for other terms of the restructuring, and whether the debtor otherwise has access to funds at a market rate for debt with similar risk characteristics.
	A loan that is modified at a market rate of interest will not be classified as troubled debt restructuring in the calendar year subsequent to the restructuring if it is in compliance with the modified terms.  Payment performance prior and subsequent to the restructuring is taken into account in assessing whether it is likely that the borrower can meet the new terms.  Under certain circumstances, a loan may be returned to accrual at the time of restructuring.  A period of sustained repayment for at least six months generally is required for return to accrual status.
	Periodically, the Company will restructure a note into two separate notes (A/B structure), charging off the entire B portion of the note. The A note is structured with appropriate loan-to-value and cash flow coverage ratios that provide for a high likelihood of repayment. The A note is classified as a non-performing note until the borrower has displayed a historical payment performance for a reasonable time prior to and subsequent to the restructuring. A period of sustained repayment for at least six months generally is required to return the note to accrual status provided that management has determined that the performance is reasonably expected to continue. The A note will be classified as a restructured note (either performing or non-performing) through the calendar year of the restructuring that the historical payment performance has been established.
Allowance for loan and lease losses	Allowance for loan and lease losses:  The allowance for loan and lease losses (ALLL) is established through a provision for credit losses charged to expense.  Loans are charged against the ALLL when management believes that collectability of the principal is unlikely.  The allowance is an amount that management believes will be appropriate to absorb probable losses on existing loans, based on an evaluation of the collectability of loans and prior loss and recovery experience as appropriate under GAAP.  The ALLL is based on management’s evaluation of the loan portfolio giving consideration to the nature and volume of the loan portfolio, the value of underlying collateral, overall portfolio quality, review of specific problem loans, and prevailing economic conditions that may affect the borrower’s ability to pay.  While management uses the best information available to make its evaluation, future adjustments to the allowance may be necessary if there are significant changes in economic conditions.  In addition, regulatory agencies, as an integral part of their examination process, periodically review MB Financial Bank’s ALLL, and may require it to recognize adjustments to its allowance based on their judgments of information available to them at the time of their examinations.
	The ALLL is comprised of three elements: a commercial related general loss reserve; a commercial related specific reserve for impaired loans; and a consumer related reserve for smaller-balance homogenous loans.  Each element is discussed below.
	Commercial Related General Loss Reserve - We maintain a general loan loss reserve for the four categories of commercial related loans in our portfolio - commercial loans, commercial loans collateralized by the assignment of lease payments (lease loans), commercial real estate loans and construction real estate loans.
	Under our loan risk rating system, each loan, with the exception of those included in large groups of smaller-balance homogeneous consumer related loans, is risk rated between one and nine by the originating loan officer, Senior Credit Management, Loan Review or loan committee.  Loans rated "one" represent those loans least likely to default and a loan rated "nine" represents a loss.  The probability of loans defaulting for each risk rating, sometimes referred to as default factors, are estimated based on the frequency with which loans migrate from one risk rating to another and to default status over time.  We use a loan loss reserve model that incorporates the migration of loan risk ratings and historical default data over a multi-year period to develop our estimated default factors (EDFs).  The model tracks annual loan rating migrations by loan type and currently uses loan risk rating migrations for 14 years.  The migration data is adjusted by using average losses for an economic cycle (approximately 13 years) to develop EDFs by loan type, risk rating and maturity.  EDFs are updated annually in December.
	Estimated loan default factors are multiplied by individual loan balances in each risk-rating category and again multiplied by an historical loss given default estimate for each loan type (which incorporates estimated recoveries) to determine the appropriate allowance by loan type.  This approach is applied to the commercial, lease, commercial real estate, and construction real estate components of the portfolio.
	To account for current economic conditions, the general allowance for loan and lease losses also includes adjustments for macroeconomic factors.  Macroeconomic factors adjust the ALLL upward or downward based on the current point in the economic cycle using predictive economic data and are applied to the loan loss model through a separate allowance element for the commercial, commercial real estate, construction real estate and lease loan components.  To determine our macroeconomic factors, we use specific economic data that has shown to be a statistically reliable predictor of our credit losses relative to our long term average credit losses. We tested over 20 economic variables (U.S. manufacturing index, unemployment rate, U.S. GDP growth, etc.). We annually review this data to determine that such a relationship continues to exist. We currently use the following macroeconomic indicators in our macroeconomic factor computation:
	Commercial loans and lease loans:  initial unemployment insurance claims in Illinois, our prior period charge-off rates and crude oil prices.
	Commercial real estate loans and construction loans:  M2 Money stock, our prior period charge-off rates and the U.S. commercial real estate index.
	Using the indicators noted above, a predicted charge-off percentage is calculated.  The predicted charge-off percentage is then compared to the cycle average charge-off percentage, and a macroeconomic adjustment factor is calculated.  The macroeconomic adjustment factor is applied to each commercial loan type.  Each year, we review the predictive nature of the macroeconomic factors by comparing actual charge-offs to the predicted model charge-offs, re-run our regression analysis and re-calibrate the macroeconomic factors as appropriate.
	Commercial Related Specific Reserves - The ALLL also includes specific reserves on impaired commercial related loans.  A loan is considered to be impaired when management believes, after considering collection efforts and other factors, the borrower’s financial condition is such that the collection of all contractual principal and interest payments due is doubtful.
	At each quarter-end, impaired loans are reviewed individually, with adjustments made to the general calculated reserve for each loan as deemed necessary.  Specific adjustments are made depending on expected cash flows and/or the value of the collateral securing each loan.  Generally, the Company obtains a current external appraisal (within 12 months) on real estate secured impaired loans.  Our appraisal policy is designed to comply with the Interagency Appraisal and Evaluation Guidelines, most recently updated in December 2010. As part of our compliance with these guidelines, we maintain an internal Appraisal Review Department that engages and reviews all third party appraisals.
	In addition, each impaired commercial loan with real estate collateral is reviewed quarterly by our appraisal department to determine that the most recent valuation remains appropriate during subsequent quarters until the next appraisal is received.  If considered necessary by our appraisal department, the appraised value may be further discounted to reflect current values.
	Other valuation techniques are also used to value non-real estate assets.  Discounts may be applied in the impairment analysis used for general business assets (GBA).  Examples of GBA include accounts receivable, inventory, and any marketable securities pledged. The discount is used to reflect collection risk in the event of default that may not have been included in the valuation of the asset.
	Consumer Related Reserves - Pools of homogeneous loans with similar risk and loss characteristics are also assessed for probable losses.  These loan pools include consumer, residential real estate, home equity, credit cards and indirect vehicle loans.  Migration probabilities obtained from past due roll rate analyses and historical loss rates are applied to current balances to forecast charge-offs over a one-year time horizon.
	We consistently apply our methodology for determining the appropriateness of the allowance for loan and lease losses but may adjust our methodologies and assumptions based on historical information related to charge-offs and management's evaluation of the loan portfolio. In this regard, we periodically review the following to validate our allowance for loan and lease losses: historical net charge-offs as they relate to prior periods' allowance for loan and lease loss, comparison of historical loan migration in past years compared to the current year, overall credit trends and ratios and any significant changes in loan concentrations. In reviewing this data, we adjust qualitative factors within our allowance methodology to appropriately reflect any changes warranted by the validation process.
Loans acquired through transfer	Acquired loans: Purchased loans acquired in a business combination are recorded at estimated fair value on their purchase date without a carryover of the related allowance for loan and lease losses. These acquired loans are segregated into three types: pass rated loans with no discount attributable to credit quality, non-impaired loans with a discount attributable at least in part to credit quality and impaired loans with evidence of significant credit deterioration.
	•	Pass rated loans (typically performing loans) are accounted for in accordance with ASC 310-20 "Nonrefundable Fees and Other Costs" as these loans do not have evidence of credit deterioration since origination.
	•	Non-impaired loans (typically performing substandard loans) are accounted for in accordance with ASC 310-30 if they display at least some level of credit deterioration since origination.
	•	Impaired loans (typically substandard loans on non-accrual status) are accounted for in accordance with ASC 310-30 as they display significant credit deterioration since origination.
	For pass rated loans (non-purchased credit-impaired loans), the difference between the estimated fair value of the loans (computed on a loan by loan basis) and the principal outstanding is accreted over the remaining life of the loans. We anticipate recording a provision for the acquired portfolio in future quarters related to renewing Taylor loans which will largely offset the accretion from the pass rated loans.
	In accordance with ASC 310-30, for both purchased non-impaired loans and purchased impaired loans ("PCI loans"), the difference between contractually required payments at acquisition and the cash flows expected to be collected is referred to as the non-accretable difference. Further, any excess of cash flows expected at acquisition over the estimated fair value is referred to as the accretable yield and is recognized into interest income over the remaining life of the loan when there is a reasonable expectation about the amount and timing of such cash flows.
	Substantially all of the loans acquired in transactions with the FDIC displayed at least some level of credit deterioration and as such are included as non-impaired and impaired loans as described immediately above.
Lease investments	Lease investments: The Company’s investment in operating leases is reported as lease investments, net.  Rental income on operating leases is recognized as income over the lease term according to the provisions of the lease, which is generally on a straight-line basis.  The investment in equipment in operating leases is stated at cost less depreciation using the straight-line method generally over a life of five years or less.
Premises and equipment	Premises and equipment: Premises and equipment are carried at cost less accumulated depreciation and amortization.  Depreciation and amortization is computed by the straight-line method over the estimated useful lives of the assets.  Useful lives generally range from three to seven years for computer equipment and software, five to 10 years for furniture and equipment, and five to 39 years for buildings and building improvements.  Land improvements are amortized over a period of 15 years and leasehold improvements are amortized over the term of the related lease or the estimated useful lives of the improvements, whichever is shorter.  Land is not subject to depreciation.  Maintenance and repairs are charged to expense as incurred, while major improvements are capitalized and amortized to operating expense over their identified useful lives.  Premises and equipment and other long-lived assets are tested for impairment whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable from future undiscounted cash flows.  If impaired, the assets are recorded at fair value.
Other real estate owned (OREO)	Other real estate owned: Other real estate owned includes real estate assets that have been received in satisfaction of debt.  Other real estate owned is initially recorded at fair value less estimated selling costs, which establishes the cost basis.  Subsequently, other real estate owned is carried at the lower of the cost basis or fair value less estimated selling costs.  Any valuation adjustments required at the date of transfer are charged to the allowance for loan and lease losses.  Subsequently, unrealized losses and realized gains and losses on sale are included in net loss recognized on other real estate owned.
Cash surrender value of life insurance	Cash surrender value of life insurance: The Company has purchased bank-owned life insurance policies on certain executives.  Bank-owned life insurance is recorded at its cash surrender value.  Changes in the cash surrender values are included in non-interest income.
Goodwill	Goodwill: The excess of the cost of an acquisition over the fair value of the net assets acquired, including core deposit and client relationship intangibles, consists of goodwill.  Under the provisions of ASC Topic 350, goodwill is subject to at least annual assessments for impairment by applying a fair value based test.  The Company reviews goodwill and other intangible assets to determine potential impairment annually, or more frequently if events and circumstances indicate that the asset might be impaired, by comparing the carrying value of the asset with the anticipated future cash flows. The Company's annual assessment is done at the unit level. As of December 31, 2014, the annual assessment date, the Company had three reporting units: banking, leasing and mortgage banking.
Other intangibles	Other intangibles: The Company’s other intangible assets consist of core deposit and customer intangibles obtained through acquisitions.  Core deposit intangibles (the portion of an acquisition purchase price which represents value assigned to the existing deposit base) have finite lives and are amortized by the declining balance method over four to 15 years.  Other intangible assets are tested for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable from future undiscounted cash flows.  If impaired, the assets are recorded at fair value.
Mortgage Servicing Rights	Mortgage Servicing Rights: The Company originates and sells residential mortgage loans in the secondary market and may retain the right to service the loans sold. Servicing involves the collection of payments from individual borrowers and the distribution of those payments to the investors. Upon a sale of mortgage loans for which servicing rights are retained, the retained mortgage servicing rights asset is capitalized at the fair value of future net cash flows expected to be realized for performing servicing activities. Purchased mortgage servicing rights are recorded at the purchase price at the date of purchase and at fair value thereafter.
	Mortgage servicing rights do not trade in an active market with readily observable prices. The Company determines the fair value of mortgage servicing rights by estimating the fair value of the future cash flows associated with the mortgage loans being serviced. Key economic assumptions used in measuring the fair value of mortgage servicing rights include, but are not limited to, prepayment speeds, discount rates, delinquencies and cost to service. The assumptions used in the valuation model are validated on a periodic basis. The fair value is validated on a quarterly basis with an independent third party.
	The Company has elected to account for mortgage servicing rights using the fair value option. Changes in the fair value are recognized in mortgage banking revenue on the Company's Consolidated Statements of Operations.
FDIC indemnification asset	FDIC indemnification asset: As part of the Heritage Community Bank ("Heritage"), Benchmark Bank ("Benchmark"), Broadway Bank ("Broadway"), and New Century Bank ("New Century") transactions, MB Financial Bank entered into loss-share agreements with the FDIC. These agreements cover realized losses on loans and foreclosed real estate for specified periods. See Note 5 below for more information on these agreements, including the duration of MB Financial Bank’s loss-share coverage. These loss-share assets are measured separately from the loan portfolios because they are not contractually embedded in the loans and are not transferable with the loans should MB Financial Bank choose to dispose of them. Fair values at the acquisition dates were estimated based on projected cash flows available for loss-share based on the credit adjustments estimated for each loan pool and the loss-share percentages.  The loss-share assets are also separately measured from the related loans and foreclosed real estate and recorded within other assets on the balance sheet.  The corresponding accretion is recorded in other income on the statement of operations.  Although these assets are contractual receivables from the FDIC, there are no contractual interest rates.
	When cash flow estimates are adjusted downward for a particular loan pool, the FDIC indemnification asset is increased.  An allowance for loan and lease losses is established for the impairment of the loans.  A provision for credit losses is recognized for the difference between the increase in the FDIC indemnification asset and the decrease in cash flows.
	When cash flow estimates are adjusted upward for a particular loan pool, the FDIC indemnification asset is decreased.  The difference between the decrease in the FDIC indemnification asset and the increase in cash flows is accreted over the estimated life of the loan pool.
	When cash flow estimates are adjusted downward for covered foreclosed real estate, the FDIC indemnification asset is increased.  A charge is recognized for the difference between the increase in the FDIC indemnification asset and the decrease in cash flows.
	When cash flow estimates are adjusted upward for covered foreclosed real estate, the FDIC indemnification asset is decreased.  Any write-down after the transfer to covered foreclosed real estate is reversed.
	In both scenarios, the claw-back liability for amounts owed to the FDIC for better than expected performance will increase or decrease accordingly.
Preferred stock	Preferred stock: Preferred stock issued in connection with the Taylor Capital Group, Inc. merger was initially recorded at fair value.  Preferred dividends declared are deducted from net income for computing income available to common stockholders and earnings per common share computations.
Treasury stock	Treasury stock: Treasury stock is recorded at acquisition cost. Gains and losses on disposition are recorded as increases or decreases to additional paid-in capital with losses in excess of previously recorded gains charged directly to retained earnings.
Derivative financial instruments and hedging activities	Derivative financial instruments and hedging activities: ASC Topic 815 establishes accounting and reporting standards requiring that every derivative instrument (including certain derivative instruments embedded in other contracts) be recorded in the balance sheet as either an asset or liability measured at its fair value.  ASC Topic 815 requires that changes in the derivative’s fair value be recognized currently in earnings unless specific hedge accounting criteria are met.  Accounting for qualifying hedges allows a derivative’s gains and losses to offset related results on the hedged item in the statement of operations, and requires that a company must formally document, designate and assess the effectiveness of transactions that receive hedge accounting.
	All derivatives are recognized on the consolidated balance sheet at their fair value.  On the date the derivative contract is entered into, the Company designates the derivative as either a fair value hedge (i.e. a hedge of the fair value of a recognized asset or liability), a cash flow hedge (i.e. a hedge of the variability of cash flows to be received or paid related to a recognized asset or liability), or a non-designated derivative (i.e. an instrument with no hedging designation).  For a derivative designated as a fair value hedge, the changes in the fair value of the derivative and of the hedged item attributable to the hedged risk are recognized in earnings.  If the derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in other comprehensive income and are recognized in the statement of operations when the hedged item affects earnings.  Ineffective portions of changes in the fair value of cash flow hedges are recognized in earnings.  Changes in the fair value of derivatives that are not designated as fair value or cash flow are reported currently in earnings, as noninterest income.
	The Company formally documents all relationships between hedging instruments and hedging items, as well as its risk management objective and strategy for undertaking various hedge transactions.  This process includes linking all derivatives that are designated as fair value hedges or cash flow hedges to specific assets or liabilities on the balance sheet.  The Company also formally assesses, both at the hedge’s inception and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in fair values or cash flows of hedged items.
	The Company discontinues hedge accounting prospectively when it is determined that the derivative is no longer effective in offsetting changes in the fair value or cash flows of the hedged item; the derivative expires or is sold, terminated, or exercised; or management determines that designation of the derivative as a hedging instrument is no longer appropriate.  When hedge accounting is discontinued because it is determined that the derivative no longer qualifies as an effective fair value hedge, the Company continues to carry the derivative on the balance sheet at its fair value, and no longer adjusts the hedged asset or liability for changes in fair value. The adjustment of the carrying amount of the hedged asset or liability is accounted for in the same manner as other components of the carrying amount of that asset or liability.
Transfers of financial assets	Transfers of financial assets: Transfers of financial assets are accounted for as sales, when control over the assets has been surrendered.  Control over transferred assets is deemed to be surrendered when the assets have been isolated from the Company, the transferee obtains the right (free of conditions that constrain it from taking advantage of the right) to pledge or exchange the transferred assets, and the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Sale of maintenance contracts	Sale of maintenance contracts: LaSalle Business Solutions, LLC (LBS), a subsidiary of LaSalle Systems Leasing, Inc., sells third party maintenance contracts to customers.  The maintenance is serviced by third party providers, with LBS maintaining no legal obligation under the contract to perform additional services.  Revenues are recorded net of cost of sales, as LBS is viewed as an agent under ASC Topic 605, accepting minimal credit risk, maintaining no obligation to perform maintenance under the contracts and having no control over selection of the maintenance supplier.
Asset management and trust assets	Asset management and trust assets: Assets of the asset management and trust department, other than trust cash on deposit at MB Financial Bank, are not included in these consolidated financial statements because they are not assets of the bank.
Stock-based compensation	Stock-based compensation: The Company accounts for its equity awards in accordance with ASC Topic 718.  ASC Topic 718 requires companies to recognize compensation expense related to equity awards in their statement of operations.  See Note 19 below for more information.
Income taxes	Income taxes: Deferred taxes are provided on a liability method whereby deferred tax assets are recognized for deductible temporary differences, operating loss carryforwards and tax credit carryforwards, while deferred tax liabilities are recognized for taxable temporary differences.  Temporary differences are the differences between the reported amounts of assets and liabilities and their tax bases.  Deferred tax assets are reduced by a valuation allowance when, in the opinion of management, it is more likely than not that some portion or all of the deferred tax assets will not be realized.  Deferred tax assets and liabilities are adjusted for the effects of changes in tax laws and rates on the date of enactment.
Basic and diluted earnings per common share	Basic and diluted earnings per common share: Earnings per common share is computed using the two-class method. Basic earnings per common share is computed by dividing net income available to common stockholders 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, though no actual shares of common stock related to restricted stock units are issued until the settlement of such units, to the extent holders of these securities receive non-forfeitable dividends or dividend equivalents at the same rate as holders of the Company's common stock. 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.
Comprehensive income	Comprehensive income: Comprehensive income consists of net income and other comprehensive income.  Other comprehensive income includes unrealized gains and losses on securities available-for-sale, net of deferred taxes, which are reported as a separate component of stockholders’ equity on the consolidated balance sheet.
Segment Reporting	Segment Reporting: An operating segment is a component of an entity that: (i) engages in business activities from which it may earn revenues and incur expenses; (ii) has operating results that are reviewed regularly by the entity’s chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance; and (iii) has discrete financial information available. As of December 31, 2014, the Company had three reportable operating segments: banking, leasing and mortgage banking.
New authoritative accounting guidance	New authoritative accounting guidance:
	ASC Topic 740 “Income Taxes.” New authoritative accounting guidance under ASC Topic 740, “Income Taxes” amended prior guidance to include explicit guidance on the financial statement presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. An unrecognized tax benefit, or a portion of an unrecognized tax benefit, should be presented in the financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward, except as follows. To the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position or the tax law of the applicable jurisdiction does not require the entity to use, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. The Company adopted this new authoritative guidance on January 1, 2014, and it did not have an impact on the Company's statements of operations or financial condition.
	ASC Topic 310 “Receivables.” New authoritative accounting guidance under ASC Topic 310, “Receivables” amended prior guidance to clarify that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical
	possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. Additionally, the amendments require interim and annual disclosures. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have a significant impact on the Company's statements of operations or financial condition.
	ASC Topic 323 “Investments - Equity Method and Joint Ventures.” New authoritative accounting guidance under ASC Topic 323, “Investments - Equity Method and Joint Ventures” amended prior guidance to permit entities to make an accounting policy election to account for their investments in qualified affordable housing projects using the proportional amortization method if certain conditions are met. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the net investment performance in the statement of operation as a component of income tax expense. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have a significant impact on the Company's statements of operations or financial condition.
	ASC Topics 205 “Presentation of Financial Statements” and 360 “Property, Plant, and Equipment.” New authoritative accounting guidance under ASC Topic 205, “Presentation of Financial Statements” and ASC Topic 360 “Property, Plant, and Equipment” amended prior guidance to change the requirements for reporting discontinued operations. The disposal of a component of an entity or group of components of an entity is required to be reported in discontinued operations if the disposal represents a strategic shift that has (or will have) a major effect on an entity's operations and financial results. The new authoritative guidance also requires additional disclosures about discontinued operations. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have an impact on the Company's statements of operations or financial condition.
	ASC Topic 860 “Transfers and Servicing.” New authoritative accounting guidance under ASC Topic 860, “Transfers and Servicing” amended prior guidance to change the accounting for repurchase-to-maturity transactions to secured borrowing accounting and to require separate accounting for a transfer of a financial asset executed contemporaneously with a repurchase agreement with the same counterparty, which will result in secured borrowing accounting for the repurchase agreement. The new authoritative guidance also requires disclosures for a transfer of a financial asset accounted for as a sale and an agreement with the same transferee entered into in contemplation of the initial transfer that results in the transferor retaining substantially all of the exposure to the economic return on the transferred financial asset throughout the term of the transaction. The new authoritative guidance will be effective for reporting periods after January 1, 2015, and the Company is assessing the impact on the statements of operations and financial condition.
	ASC Topic 718 “Compensation - Stock Compensation.” New authoritative accounting guidance under ASC Topic 718, “Compensation - Stock Compensation” amended prior guidance to require that a performance target that affects vesting and that could be achieved after the requisite service period be treated as a performance condition. The new authoritative guidance will be effective for reporting periods after January 1, 2015 and is not expected to have an impact on the Company's statements of operations or financial condition.
Reclassifications	Reclassifications: Certain prior period amounts have been reclassified to conform to current period presentation.  These reclassifications did not result in any changes to previously reported net income or stockholders’ equity.

Significant_Accounting_Policie2

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Reconciliation of the number of shares used in the calculation of basic and diluted earnings (loss) per common share	The following table presents a reconciliation of the number of shares used in the calculation of basic and diluted earnings per common share (amounts in thousands, except common share data):
		Years Ended
		December 31,
		2014		2013		2012
	Distributed earnings allocated to common stock	$	34,422	$	24,290	$	7,149
	Undistributed earnings	51,679		74,165		83,225
	Net income	86,101		98,455		90,374
	Less: preferred stock dividends and discount accretion	4,000		—		3,269
	Net income available to common stockholders	82,101		98,455		87,105
	Less: earnings and dividends allocated to participating securities	2		2		3
	Earnings allocated to common stockholders	$	82,099	$	98,453	$	87,102
	Weighted average shares outstanding for basic earnings per common share	62,012,196		54,509,612		54,270,297
	Dilutive effect of equity awards	561,210		484,253		235,679
	Weighted average shares outstanding for diluted earnings per common share	62,573,406		54,993,865		54,505,976
	Basic earnings per common share	$	1.32	$	1.81	$	1.61
	Diluted earnings per common share	1.31		1.79		1.6

Business_Combinations_Tables

Business Combinations (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Assets Acquired and Liabilities Assumed	Estimated fair values of the assets acquired and liabilities assumed in the Taylor Capital transaction, as of the closing date of the transaction were as follows (in thousands):
		August 18,
		2014
	ASSETS
	Cash and cash equivalents	$	154,684
	Investment securities available for sale	826,691
	Investment securities held to maturity	22,599
	Non-marketable securities - FRB and FHLB Stock	50,620
	Loans held for sale	670,671
	Loans	3,532,211
	Leases investments, net	11,885
	Premises and equipment	19,701
	Goodwill	288,152
	Core deposit intangible	20,079
	Mortgage servicing rights	224,453
	Other real estate owned	4,720
	Other assets	130,478
	Total assets	$	5,956,944
	LIABILITIES
	Deposits	$	3,953,213
	Short-term borrowings	1,035,800
	Junior subordinated notes issued to capital trusts	80,843
	Accrued expenses and other liabilities	123,028
	Total liabilities	$	5,192,884
	Series A preferred stock at $28.82 per share at August 15, 2014	$	115,280
	Total identifiable net assets less Series A preferred stock	$	648,780
	Consideration excluding Series A preferred stock:
	Market value of common stock at $26.49 per share at August 15, 2014 (19,602,482 shares of common stock issued)	$	519,270
	Cash paid	129,510
	Total fair value of consideration, excluding Series A preferred stock	$	648,780
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period	The following table presents the acquired loans as of the acquisition date (in thousands):
		PCI Loans			Non-PCI Loans
	Contractually required principal and interest payments	$	244,650		$	3,707,463
	Contractually required interest payments not expected to be collected due to estimated prepayments	—			(302,329		)
	Nonaccretable difference	(34,219		)	—
	Cash flows expected to be collected	210,431			3,405,134
	Accretable difference	(5,626		)	(77,728		)
	Fair value of acquired loans	$	204,805		$	3,327,406
Business Acquisition, Pro Forma Information	The following table provides the unaudited pro forma information for the results of operations for the years ended December 31, 2014 and 2013, as if the acquisition had occurred January 1, 2013. The pro forma results combine the historical results of Taylor Capital into the Company's consolidated statement of income including the impact of certain purchase accounting adjustments including loan discount accretion, investment securities discount accretion, intangible assets amortization, deposit premium accretion and borrowing discount amortization. The pro forma results have been prepared for comparative purposes only and are not necessarily indicative of the results that would have been obtained had the acquisition actually occurred on January 1, 2013. No assumptions have been applied to the pro forma results of operations regarding possible revenue enhancements, provision for credit losses, expense efficiencies or asset dispositions. The merger related expenses that have been recognized are included in net income in the table below.
		For Years Ended December 31,
		2014			2013
	(in thousands)
	Total revenues (net interest income plus non-interest income)	$	774,778		$	790,655
	Net income	112,220			180,085

Investment_Securities_Tables

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Summary investment holdings	and fair values of investment securities were as follows (in thousands):
		Amortized			Gross			Gross			Fair
		Cost			Unrealized			Unrealized			Value
					Gains			Losses
	December 31, 2014
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	64,612		$	1,281		$	(20	)	$	65,873
	States and political subdivisions	390,076			20,846			(68		)	410,854
	Residential mortgage-backed securities	713,413			8,977			(1,827		)	720,563
	Commercial mortgage-backed securities	186,110			1,772			(220		)	187,662
	Corporate bonds	259,526			2,428			(2,751		)	259,203
	Equity securities	10,531			66			—			10,597
		1,624,268			35,370			(4,886		)	1,654,752
	Held to Maturity
	States and political subdivisions	752,558			30,089			(382		)	782,265
	Residential mortgage-backed securities	240,822			11,974			—			252,796
		993,380			42,063			(382		)	1,035,061
	Total	$	2,617,648		$	77,433		$	(5,268	)	$	2,689,813
	December 31, 2013
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	50,486		$	1,704		$	(122	)	$	52,068
	States and political subdivisions	19,398			22			(277		)	19,143
	Residential mortgage-backed securities	696,415			8,555			(3,737		)	701,233
	Commercial mortgage-backed securities	50,891			2,050			—			52,941
	Corporate bonds	284,083			1,597			(2,610		)	283,070
	Equity securities	10,649			—			(192		)	10,457
		1,111,922			13,928			(6,938		)	1,118,912
	Held to Maturity
	States and political subdivisions	932,955			7,584			(4,366		)	936,173
	Residential mortgage-backed securities	249,578			13,178			—			262,756
		1,182,533			20,762			(4,366		)	1,198,929
	Total	$	2,294,455		$	34,690		$	(11,304	)	$	2,317,841
Unrealized losses on investment securities and the fair value of the related securities	Unrealized losses on investment securities and the fair value of the related securities at December 31, 2014 were as follows (in thousands):
		Less Than 12 Months						12 Months or More						Total
		Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
		Value			Losses			Value			Losses			Value		Losses
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	9,644		$	(20	)	$	—		$	—		$	9,644	$	(20	)
	States and political subdivisions	7,784			(21		)	3,558			(47		)	11,342		(68		)
	Residential mortgage-backed securities	235,818			(1,336		)	29,373			(491		)	265,191		(1,827		)
	Commercial mortgage-backed securities	89,509			(220		)	—			—			89,509		(220		)
	Corporate bonds	62,693			(1,159		)	9,675			(1,592		)	72,368		(2,751		)
		405,448			(2,756		)	42,606			(2,130		)	448,054		(4,886		)
	Held to Maturity
	States and political subdivisions	28,786			(130		)	14,238			(252		)	43,024		(382		)
	Totals	$	434,234		$	(2,886	)	$	56,844		$	(2,382	)	$	491,078	$	(5,268	)
	Unrealized losses on investment securities and the fair value of the related securities at December 31, 2013 were as follows (in thousands):
		Less Than 12 Months						12 Months or More						Total
		Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
		Value			Losses			Value			Losses			Value		Losses
	Available for Sale
	U.S. Government sponsored agencies and enterprises	$	18,598		$	(122	)	$	—		$	—		$	18,598	$	(122	)
	States and political subdivisions	2,275			(166		)	4,748			(111		)	7,023		(277		)
	Residential mortgage-backed securities	232,807			(2,905		)	44,182			(832		)	276,989		(3,737		)
	Corporate bonds	122,344			(2,606		)	705			(4		)	123,049		(2,610		)
	Equity securities	10,457			(192		)	—			—			10,457		(192		)
		386,481			(5,991		)	49,635			(947		)	436,116		(6,938		)
	Held to Maturity
	States and political subdivisions	235,016			(4,330		)	1,301			(36		)	236,317		(4,366		)
	Totals	$	621,497		$	(10,321	)	$	50,936		$	(983	)	$	672,433	$	(11,304	)
Summary of realized gains on the sale of investment securities available for sale	Net (losses) gains recognized on investment securities available for sale were as follows (in thousands):
		For the Years Ended December 31,
		2014			2013			2012
	Realized gains	$	2,045		$	15		$	787
	Realized losses	(4,478		)	(2		)	(8		)
	Impairment charges	(92		)	(14		)	(224		)
	Net (losses) gains	$	(2,525	)	$	(1	)	$	555
Schedule of remaining contractual maturities of securities included in the securities portfolio	The amortized cost and fair value of investment securities as of December 31, 2014 by contractual maturity are shown below. Maturities may differ from contractual maturities in mortgage-backed securities because the mortgages underlying the securities may be called or repaid without any penalties. Therefore, mortgage-backed securities are not included in the maturity categories in the following maturity summary.
		Amortized			Fair
	(In thousands)	Cost			Value
	Available for sale:
	Due in one year or less	$	13,752		$	13,792
	Due after one year through five years	305,172			306,103
	Due after five years through ten years	39,903			40,823
	Due after ten years	355,387			375,212
	Equity securities	10,531			10,597
	Residential and commercial mortgage-backed securities	899,523			908,225
		1,624,268			1,654,752
	Held to maturity:
	Due in one year or less	29,060			29,114
	Due after one year through five years	247,683			249,058
	Due after five years through ten years	102,901			106,556
	Due after ten years	372,914			397,537
	Residential mortgage-backed securities	240,822			252,796
		993,380			1,035,061
	Total	$	2,617,648		$	2,689,813

Loans_Tables

Loans (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Schedule of accounts notes financing receivable	Loans consist of the following at (in thousands):
			December 31,
			2014				2013
	Commercial		$	3,245,206			$	1,281,377
	Commercial collateralized by assignment of lease payments		1,692,258				1,494,188
	Commercial real estate		2,544,867				1,647,700
	Residential real estate		503,287				314,440
	Construction real estate		247,068				141,253
	Indirect vehicle		268,840				262,632
	Home equity		251,909				268,289
	Other consumer		78,137				66,952
	Gross loans, excluding purchased credit-impaired and covered loans		8,831,572				5,476,831
	Purchased credit-impaired and covered loans		251,645				235,720
	Total loans		$	9,083,217			$	5,712,551
Contractual aging of the recorded investment in past due loans by class of loans	The following table presents the contractual aging of the recorded investment in past due loans by class of loans as of December 31, 2014 and 2013 (in thousands):
			Current				30-59 Days				60-89 Days				Loans Past Due				Total			Total
							Past Due				Past Due				90 Days or More				Past Due
	31-Dec-14
	Commercial		$	3,231,571			$	8,222			$	—			$	5,413			$	13,635		$	3,245,206
	Commercial collateralized by assignment of lease payments		1,679,991				2,025				6,095				4,147				12,267			1,692,258
	Commercial real estate:
	Healthcare		342,984				—				—				—				—			342,984
	Industrial		333,907				944				—				3,182				4,126			338,033
	Multifamily		417,504				1,377				—				1,517				2,894			420,398
	Retail		432,718				2,481				652				2,325				5,458			438,176
	Office		244,166				—				—				2,127				2,127			246,293
	Other		754,031				307				2,421				2,224				4,952			758,983
	Residential real estate		485,492				8,038				2,319				7,438				17,795			503,287
	Construction real estate		246,731				—				—				337				337			247,068
	Indirect vehicle		265,296				2,516				702				326				3,544			268,840
	Home equity		242,756				2,717				1,039				5,397				9,153			251,909
	Other consumer		78,106				16				12				3				31			78,137
	Gross loans, excluding purchased credit-impaired and covered loans		8,755,253				28,643				13,240				34,436				76,319			8,831,572
	Purchased credit-impaired and covered loans		158,215				4,432				585				88,413				93,430			251,645
	Total loans		$	8,913,468			$	33,075			$	13,825			$	122,849			$	169,749		$	9,083,217
	Non-performing loan aging		$	46,149			$	5,764			$	1,099			$	34,075			$	40,938		$	87,087
	December 31, 2013
	Commercial		$	1,273,302			$	5,952			$	626			$	1,497			$	8,075		$	1,281,377
	Commercial collateralized by assignment of lease payments		1,489,391				3,841				656				300				4,797			1,494,188
	Commercial real estate:
	Healthcare		213,665				—				—				3,064				3,064			216,729
	Industrial		372,975				5,465				—				1,404				6,869			379,844
	Multifamily		302,456				3,078				181				2,226				5,485			307,941
	Retail		334,198				328				2,816				7,258				10,402			344,600
	Office		155,936				—				—				2,066				2,066			158,002
	Other		233,464				4,898				259				1,963				7,120			240,584
	Residential real estate		302,362				1,422				1,030				9,626				12,078			314,440
	Construction real estate		138,563				391				—				2,299				2,690			141,253
	Indirect vehicle		259,488				2,210				657				277				3,144			262,632
	Home equity		257,219				1,725				2,165				7,180				11,070			268,289
	Other consumer		66,866				81				1				4				86			66,952
	Gross loans, excluding covered loans		5,399,885				29,391				8,391				39,164				76,946			5,476,831
	Covered loans		135,717				902				3,346				95,755				100,003			235,720
	Total loans		$	5,535,602			$	30,293			$	11,737			$	134,919			$	176,949		$	5,712,551
	Non-performing loan aging		$	56,339			$	14,325			$	3,283			$	32,614			$	50,222		$	106,561
Recorded investment in nonaccrual loans and loans past due ninety days or more and still accruing by class of loans	The following table presents the recorded investment in non-accrual loans and loans past due ninety days or more and still accruing by class of loans, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
			2014								2013
							Loans past due								Loans past due
			Non-accrual				90 days or more				Non-accrual				90 days or more
							and still accruing								and still accruing
	Commercial		$	14,088			$	—			$	17,781			$	—
	Commercial collateralized by assignment of lease payments		2,404				3,566				4,276				291
	Commercial real estate:
	Healthcare		—				—				3,064				—
	Industrial		6,371				—				15,265				155
	Multifamily		5,333				—				5,145				—
	Office		3,644				464				11,703				—
	Retail		2,986				—				2,969				—
	Other		13,541				324				19,991				—
	Residential real estate		17,311				—				13,009				—
	Construction real estate		337				—				475				—
	Indirect vehicle		1,542				—				1,459				—
	Home equity		15,171				—				10,969				—
	Other consumer		5				—				9				—
	Total		$	82,733			$	4,354			$	106,115			$	446
Risk category of loans by class of loans	The following tables present the risk category of loans by class of loans based on the most recent analysis performed, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
			Pass				Special				Substandard				Doubtful				Total
							Mention
	31-Dec-14
	Commercial		$	3,036,069			$	178,984			$	30,153			$	—			$	3,245,206
	Commercial collateralized by assignment of lease payments		1,680,736				6,853				4,669				—				1,692,258
	Commercial real estate:
	Healthcare		338,622				4,362				—				—				342,984
	Industrial		314,225				8,817				14,991				—				338,033
	Multifamily		412,824				920				6,654				—				420,398
	Retail		423,842				2,740				11,594				—				438,176
	Office		229,947				8,524				7,822				—				246,293
	Other		708,447				22,013				28,523				—				758,983
	Construction real estate		246,204				527				337				—				247,068
	Total		$	7,390,916			$	233,740			$	104,743			$	—			$	7,729,399
	December 31, 2013
	Commercial		$	1,193,114			$	26,637			$	61,000			$	626			$	1,281,377
	Commercial collateralized by assignment of lease payments		1,486,899				553				6,736				—				1,494,188
	Commercial real estate:
	Healthcare		189,705				21,186				2,774				3,064				216,729
	Industrial		345,236				5,328				29,280				—				379,844
	Multifamily		296,179				342				11,420				—				307,941
	Retail		316,420				10,660				17,520				—				344,600
	Office		151,393				2,682				3,927				—				158,002
	Other		217,188				349				23,047				—				240,584
	Construction real estate		139,847				540				866				—				141,253
	Total		$	4,335,981			$	68,277			$	156,570			$	3,690			$	4,564,518
Recorded investment in loan classes based on payment activity	The following table presents the recorded investment in those loan classes based on payment activity, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
			Performing				Non-performing				Total
	31-Dec-14
	Residential real estate		$	485,976			$	17,311			$	503,287
	Indirect vehicle		267,297				1,543				268,840
	Home equity		236,739				15,170				251,909
	Other consumer		78,132				5				78,137
	Total		$	1,068,144			$	34,029			$	1,102,173
	December 31, 2013
	Residential real estate		$	301,431			$	13,009			$	314,440
	Indirect vehicle		261,173				1,459				262,632
	Home equity		257,320				10,969				268,289
	Other consumer		66,943				9				66,952
	Total		$	886,867			$	25,446			$	912,313
Loans individually evaluated for impairment by class of loans	The following tables present loans individually evaluated for impairment by class of loans, excluding purchased credit-impaired and covered loans, as of December 31, 2014 and 2013 (in thousands):
			31-Dec-14
			Unpaid				Recorded				Partial				Allowance for				Average			Interest
			Principal				Investment				Charge-offs				Loan and Lease Losses				Recorded			Income
			Balance												Allocated				Investment			Recognized
	With no related allowance recorded:
	Commercial		$	9,752			$	8,992			$	760			$	—			$	10,324		$	—
	Commercial collateralized by assignment of lease payments		2,316				2,316				—				—				2,569			121
	Commercial real estate:
	Healthcare		—				—				—				—				—			—
	Industrial		9,115				5,858				3,257				—				7,870			—
	Multifamily		1,733				1,733				—				—				1,928			52
	Retail		2,025				813				1,212				—				3,465			—
	Office		—				—				—				—				1,127			—
	Other		1,479				1,465				14				—				5,249			—
	Residential real estate		1,941				1,941				—				—				2,740			—
	Construction real estate		—				—				—				—				34			—
	Indirect vehicle		—				—				—				—				—			—
	Home equity		577				577				—				—				762			—
	Other consumer		—				—				—				—				—			—
	With an allowance recorded:
	Commercial		7,987				7,987				—				2,395				14,227			—
	Commercial collateralized by assignment of lease payments		715				715				—				105				1,515			91
	Commercial real estate:
	Healthcare		—				—				—				—				—			—
	Industrial		517				513				4				130				4,982			—
	Multifamily		5,680				4,709				971				996				6,354			131
	Retail		9,264				7,897				1,367				720				8,547			—
	Office		4,528				2,986				1,542				545				2,833			—
	Other		12,612				12,527				85				136				11,022			12
	Residential real estate		14,234				14,234				—				3,126				14,632			—
	Construction real estate		2,707				337				2,370				162				455			—
	Indirect vehicle		227				227				—				14				358			—
	Home equity		25,927				25,705				222				2,153				25,672			—
	Other consumer		—				—				—				—				—			—
	Total		$	113,336			$	101,532			$	11,804			$	10,482			$	126,665		$	407
			December 31, 2013
			Unpaid				Recorded				Partial				Allowance for				Average			Interest
			Principal				Investment				Charge-offs				Loan and Lease Losses				Recorded			Income
			Balance												Allocated				Investment			Recognized
	With no related allowance recorded:
	Commercial		$	8,903			$	8,903			$	—			$	—			$	8,259		$	—
	Commercial collateralized by assignment of lease payments		3,401				3,401				—				—				1,030			6
	Commercial real estate:
	Healthcare		—				—				—				—				2,698			—
	Industrial		7,560				7,560				—				—				8,900			—
	Multifamily		1,166				1,166				—				—				758			11
	Retail		4,466				4,466				—				—				3,628			—
	Office		559				527				32				—				922			—
	Other		2,963				2,963				—				—				4,380			—
	Residential real estate		4,234				4,234				—				—				3,260			—
	Construction real estate		—				—				—				—				—			—
	Indirect vehicle		—				—				—				—				—			—
	Home equity		577				577				—				—				797			—
	Other consumer		—				—				—				—				—			—
	With an allowance recorded:
	Commercial		8,923				8,919				4				4,284				13,476			4
	Commercial collateralized by assignment of lease payments		1,060				1,060				—				144				1,279			192
	Commercial real estate:
	Healthcare		3,186				3,064				122				382				8,189			—
	Industrial		7,707				7,705				2				3,038				3,699			—
	Multifamily		5,374				5,374				—				1,661				6,443			340
	Retail		14,169				12,428				1,741				1,511				12,885			280
	Office		2,442				2,442				—				791				4,045			—
Other		20,367				17,029				3,338				796				12,868			20
Residential real estate		13,496				12,710				786				3,119				12,966			245
Construction real estate		475				475				—				227				1,603			—
Indirect vehicle		173				123				50				57				86			—
Home equity		23,840				23,395				445				1,358				24,283			772
Other consumer		—				—				—				—				—			—
Total		$	135,041			$	128,521			$	6,520			$	17,368			$	136,454		$	1,870
Schedule of loans that have been restructured classified as performing and non-performing	The following table presents loans that have been restructured during the year ended December 31, 2014 (dollars in thousands):
			31-Dec-14
			Number of		Pre-Modification Recorded				Post-Modification Recorded				Charge-offs and
			Loans		Investment				Investment				Specific Reserves
	Performing:
	Residential real estate		3		$	588			$	588			$	—
	Indirect vehicle		2		26				26				—
	Home equity		9		2,251				2,251				—
	Total		14		$	2,865			$	2,865			$	—
	Non-Performing:
	Commercial		1		$	263			$	263			$	85
	Commercial real estate:
	Multifamily		1		158				158				40
	Residential real estate		6		1,850				1,850				246
	Indirect vehicle		53		320				320				88
	Home equity		27		3,813				3,813				335
	Total		88		$	6,404			$	6,404			$	794
	The following table presents loans that have been restructured during the year ended December 31, 2013 (dollars in thousands):
			December 31, 2013
			Number of			Pre-Modification Recorded				Post-Modification Recorded				Charge-offs and
			Loans			Investment				Investment				Specific Reserves
	Performing:
	Commercial real estate:
	Multifamily		1			$	601			$	601			$	—
	Residential real estate		6			910				910				—
	Home equity		14			2,204				2,204				—
	Total		21			$	3,715			$	3,715			$	—
	Non-Performing:
	Commercial		2			$	1,251			$	1,251			$	673
	Commercial collateralized by assignment of lease payments		1			3,401				3,401				—
	Commercial real estate:
	Healthcare		1			3,164				3,164				496
	Industrial		4			2,570				2,570				1,425
	Multifamily		2			623				623				169
	Retail		3			862				862				235
	Other		1			84				84				23
	Residential real estate		9			1,803				1,682				121
	Indirect vehicle		26			171				129				42
	Home equity		26			3,430				3,430				—
	Total		75			$	17,359			$	17,196			$	3,184
Troubled debt restructuring activity rollforward	The following tables present the troubled debt restructurings activity during the year ended December 31, 2014 (dollars in thousands):
			Performing				Non-performing
	Beginning balance		$	29,430			$	24,952
	Additions		2,865				6,404
	Charge-offs		(451		)		(2,840		)
	Principal payments, net		(2,650		)		(3,965		)
	Removals		(8,574		)		(3,576		)
	Transfer to other real estate owned		—				(221		)
	Transfer from non-performing/performing		6,407				11,424
	Transfer to non-performing/performing		(11,424		)		(6,407		)
	Ending balance		$	15,603			$	25,771
Type of financing receivable modifications and restructuring	The following table presents the type of modification for loans that have been restructured and the post-modification recorded investment during the year ended December 31, 2014 (dollars in thousands):
		December 31, 2014
		Extended				Extended Maturity				Extended
		Maturity,				and Amortization,				Maturity and				Delay in
		Amortization				Delay in Payments				Delay in Payments				Payments or
		and Reduction				and Reduction of				or Reduction of				Reduction of
		of Interest Rate				Interest Rate				Interest Rate				Interest Rate				Total
	Commercial	$	—			$	—			$	263			$	—			$	263
	Commercial real estate:
	Multifamily	—				—				158				—				158
	Residential real estate	411				—				1,268				759				2,438
	Indirect vehicle	—				—				—				346				346
	Home equity	2,384				878				1,211				1,591				6,064
	Total	$	2,795			$	878			$	2,900			$	2,696			$	9,269
Activity in the allowance for loan losses	Activity in the allowance for loan and lease losses was as follows (in thousands):
			Year Ended December 31,
			2014				2013				2012
	Balance at beginning of year		$	113,462			$	128,279			$	135,975
	Allowance for unfunded credit commitments acquired through business combination		1,261				—				—
	Utilization of allowance for unfunded credit commitments		(637		)		—				—
	Provision for credit losses		12,052				(5,804		)		(8,900		)
	Charge-offs:
	Commercial		1,339				3,706				2,408
	Commercial collateralized by assignment of lease payments		586				—				1,721
	Commercial real estate		11,438				7,517				11,377
	Residential real estate		1,718				2,796				2,944
	Construction real estate		79				980				4,007
	Indirect vehicle		3,735				2,911				2,259
	Home equity		3,383				3,692				4,551
	Other consumer		2,467				2,073				1,349
	Total charge-offs		24,745				23,675				30,616
	Recoveries:
	Commercial		3,757				3,156				3,475
	Commercial collateralized by assignment of lease payments		939				1,131				6,720
	Commercial real estate		4,020				6,025				16,987
	Residential real estate		1,190				479				501
	Construction real estate		252				1,616				2,019
	Indirect vehicle		1,736				1,411				1,096
	Home equity		482				594				671
	Other consumer		288				250				351
	Total recoveries		12,664				14,662				31,820
	Net charge-offs (recoveries)		12,081				9,013				(1,204		)
	Allowance for credit losses		114,057				113,462				128,279
	Allowance for unfunded credit commitments		(4,031		)		(1,716		)		(4,075		)
	Balance at December 31,		$	110,026			$	111,746			$	124,204
Allowance activity for loan losses by portfolio segment based on impairment method	The following table presents the activity in the allowance for credit losses, balance in allowance for credit losses and recorded investment in loans by portfolio segment and based on impairment method as of December 31, 2014 and 2013 (in thousands):
			Commercial				Commercial				Commercial				Residential				Construction			Indirect		Home		Other Consumer		Unfunded			Total
							collateralized  by				real estate				real estate				real estate			vehicle		equity				Commitments
							assignment of
							lease payments
	December 31, 2014
	Allowance for credit losses:
	Beginning balance		$	23,461			$	9,159			$	51,628			$	8,872			$	6,856		$	1,662	$	8,478	$	1,630	$	1,716		$	113,462
	Allowance for unfunded credit commitments acquired through business combination		—				—				—				—				—			—		—		—		1,261			1,261
	Utilization of allowance for unfunded credit commitments		—				—				—				—				—			—		—		—		(637		)	(637		)
	Charge-offs		1,339				586				11,438				1,718				79			3,735		3,383		2,467		—			24,745
	Recoveries		3,757				939				4,020				1,190				252			1,736		482		288		—			12,664
	Provision		3,692				450				(2,384		)		(1,698		)		1,889			2,024		3,879		2,509		1,691			12,052
	Ending balance		$	29,571			$	9,962			$	41,826			$	6,646			$	8,918		$	1,687	$	9,456	$	1,960	$	4,031		$	114,057
	Ending allowance balance attributable to loans:
	Individually evaluated for impairment		$	2,395			$	105			$	2,527			$	3,126			$	162		$	14	$	2,153	$	—	$	1,348		$	11,830
	Collectively evaluated for impairment		26,684				9,857				38,517				3,520				8,747			1,673		7,303		1,960		2,683			100,944
	Acquired and accounted for under ASC 310-30 (1)		492				—				782				—				9			—		—		—		—			1,283
	Total ending allowance balance		$	29,571			$	9,962			$	41,826			$	6,646			$	8,918		$	1,687	$	9,456	$	1,960	$	4,031		$	114,057
	Loans:
	Individually evaluated for impairment		$	16,979			$	3,031			$	38,501			$	16,175			$	337		$	227	$	26,282	$	—	$	—		$	101,532
	Collectively evaluated for impairment		3,228,227				1,689,227				2,506,366				487,112				246,731			268,613		225,627		78,137		—			8,730,040
	Acquired and accounted for under ASC 310-30 (1)		103,582				—				80,378				14,138				31,068			—		138		22,341		—			251,645
	Total ending loans balance		$	3,348,788			$	1,692,258			$	2,625,245			$	517,425			$	278,136		$	268,840	$	252,047	$	100,478	$	—		$	9,083,217
	December 31, 2013
	Allowance for credit losses:
	Beginning balance		$	24,943			$	7,755			$	61,056			$	6,941			$	11,222		$	1,324	$	9,401	$	1,562	$	4,075		$	128,279
	Transfer to (from) allowance for unfunded credit commitments		—				—				—				—				500			—		—		—		(500		)	—
	Charge-offs		3,706				—				7,517				2,796				980			2,911		3,692		2,073		—			23,675
	Recoveries		3,156				1,131				6,025				479				1,616			1,411		594		250		—			14,662
	Provision		(932		)		273				(7,936		)		4,248				(5,502		)	1,838		2,175		1,891		(1,859		)	(5,804		)
	Ending balance		$	23,461			$	9,159			$	51,628			$	8,872			$	6,856		$	1,662	$	8,478	$	1,630	$	1,716		$	113,462
	Ending allowance balance attributable to loans:
	Individually evaluated for impairment		$	4,284			$	144			$	8,179			$	3,119			$	227		$	57	$	1,358	$	—	$	689		$	18,057
	Collectively evaluated for impairment		18,693				9,015				41,763				5,753				6,567			1,605		7,120		1,630		1,027			93,173
	Acquired and accounted for under ASC 310-30 (1)		484				—				1,686				—				62			—		—		—		—			2,232
	Total ending allowance balance		$	23,461			$	9,159			$	51,628			$	8,872			$	6,856		$	1,662	$	8,478	$	1,630	$	1,716		$	113,462
	Loans:
	Individually evaluated for impairment		$	17,822			$	4,461			$	64,724			$	16,944			$	475		$	123	$	23,972	$	—	$	—		$	128,521
	Collectively evaluated for impairment		1,246,523				1,489,727				1,582,976				293,883				140,778			262,509		244,317		66,952		—			5,327,665
	Acquired and accounted for under ASC 310-30 (1)		35,673				—				140,504				5,448				48,313			—		107		26,320		—			256,365
	Total ending loans balance		$	1,300,018			$	1,494,188			$	1,788,204			$	316,275			$	189,566		$	262,632	$	268,396	$	93,272	$	—		$	5,712,551
	(1)  Loans acquired in the Taylor Capital merger and FDIC-assisted transactions and accounted for under ASC Subtopic 310-30 “Receivables — Loans and Debt Securities Acquired with Deteriorated Credit Quality.”
Changes in the accretable yield for purchased credit-impaired loans	Changes in the accretable yield for loans acquired and accounted for under ASC 310-30 were as follows for the years ended December 31, 2014 and 2013 (in thousands):
			Year Ended December 31,
			2014				2013
	Balance at beginning of period		$	2,337			$	5,685
	Purchases		5,626				—
	Accretion		(2,098		)		(4,456		)
	Other		1,569				1,108
	Balance at end of period		$	7,434			$	2,337
Purchased loans disclosures	The carrying amount of covered loans and other purchased non-covered loans at December 31, 2014 consisted of purchased credit-impaired loans and non-credit-impaired loans as shown in the following table (in thousands):
	31-Dec-14		Purchased				Purchased  Non-Impaired				Total
			Impaired				Loans
			Loans
	Covered loans:
	Commercial related (1)		$	706			$	2,099			$	2,805
	Commercial		830				309				1,139
	Commercial real estate		20,489				16,528				37,017
	Construction real estate		2,512				2,085				4,597
	Other		1,877				21,622				23,499
	Total covered loans		$	26,414			$	42,643			$	69,057
	Estimated (payable) receivable amount from the FDIC under the loss-share agreement (2)		$	(1,850	)		$	4,513			$	2,663
	Non covered loans:
	Commercial related (3)		$	4,288			$	13,370			$	17,658
	Commercial loans		95,350				1,681,908				1,777,258
	Commercial loans collateralized by assignment of lease payments		—				160,299				160,299
	Commercial real estate		43,361				926,184				969,545
	Construction real estate		26,471				146,567				173,038
	Other		13,118				231,921				245,039
	Total non-covered loans		$	182,588			$	3,160,249			$	3,342,837
	-1	Covered commercial related loans include commercial, commercial real estate and construction real estate loans acquired in connection with the Benchmark FDIC-assisted transactions.
	-2	Estimated reimbursable amounts from the FDIC under the loss-share agreement exclude $303 thousand in reimbursable amounts related to covered other real estate owned.
	-3	Non-covered commercial related loans include commercial, commercial real estate and construction real estate for InBank and Heritage.

Lease_Investments_Tables

Lease Investments (Tables)	12 Months Ended
	Dec. 31, 2014
Lease Investments
Schedule of lease investments by categories	Lease investments by categories follow (in thousands):
		December 31,
		2014			2013
	Direct finance leases:
	Minimum lease payments	$	340,602		$	155,945
	Estimated unguaranteed residual values	70,469			31,272
	Less: unearned income	(31,229		)	(14,473		)
	Direct finance leases (1)	$	379,842		$	172,744
	Leveraged leases:
	Minimum lease payments	$	10,689		$	24,320
	Estimated unguaranteed residual values	1,586			2,508
	Less: unearned income	(540		)	(1,644		)
	Less: related non-recourse debt	(10,330		)	(23,243		)
	Leveraged leases (1)	$	1,405		$	1,941
	Operating leases:
	Equipment, at cost	$	257,495		$	218,473
	Less accumulated depreciation	(94,662		)	(87,384		)
	Lease investments, net	$	162,833		$	131,089
	(1)Direct finance and leveraged leases are included as commercial loans collateralized by assignment of lease payments for financial
	statement purposes.
Schedule of minimum lease payments receivable for the various categories of leases due	The minimum lease payments receivable for the various categories of leases are due as follows (in thousands) for the years ending December 31,
		Direct			Leveraged			Operating
		Finance
	Year	Leases			Leases			Leases			Total
	2015	$	122,353		$	7,386		$	40,624		$	170,363
	2016	97,324			2,482			29,802			129,608
	2017	66,223			642			20,461			87,326
	2018	37,231			179			9,475			46,885
	2019	13,457			—			5,143			18,600
	Thereafter	4,014			—			3,205			7,219
		$	340,602		$	10,689		$	108,710		$	460,001
Schedule of residual values for leases by category in the year the initial lease term ends	At December 31, 2014, the following reflects the residual values for leases by category in the year the initial lease term ends (in thousands):
		Residual Values
		Direct
	End of initial lease term	Finance			Leveraged			Operating
	December 31,	Leases			Leases			Leases			Total
	2015	$	8,827		$	856		$	2,818		$	12,501
	2016	7,597			606			7,926			16,129
	2017	19,448			105			10,332			29,885
	2018	14,544			19			9,265			23,828
	2019	10,551			—			7,857			18,408
	Thereafter	9,502			—			19,050			28,552
		$	70,469		$	1,586		$	57,248		$	129,303
Income from lease investments	Income from lease financing, net was composed of (in thousands):
		Years Ended December 31,
		2014			2013			2012
	Rental income	$	64,017		$	62,629		$	49,473
	Equipment maintenance contracts revenue, net of cost of sales	16,441			11,071			14,129
	Vendor promotional income	8,382			7,587			4,051
	Other lease related revenue	2,121			1,796			167
	Gain on sale of lease payments and leased equipment, net of residual write downs	12,899			12,002			4,708
	Income on lease investments, gross	103,860			95,085			72,528
	Less: depreciation on operating leases	(39,550		)	(33,842		)	(36,146		)
	Lease financing, net	$	64,310		$	61,243		$	36,382

Premises_and_Equipment_Tables

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Schedule of premises and equipment	Premises and equipment consisted of (in thousands):
		December 31,
		2014			2013
	Land and land improvements	$	67,630		$	67,389
	Buildings	100,505			98,675
	Furniture and equipment	124,490			97,766
	Buildings and leasehold improvements	59,733			55,639
		352,358			319,469
	Accumulated depreciation	(113,981		)	(98,404		)
	Premises and equipment, net	$	238,377		$	221,065

Goodwill_and_Intangibles_Table

Goodwill and Intangibles (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying amount of core deposit and client relationship intangibles	The following table presents the changes in the carrying amount of core deposit and client relationship intangibles, gross carrying amount, accumulated amortization, and net book value as of December 31, 2014 and 2013 (in thousands):
			December 31,
			2014			2013
	Balance at beginning of period		$	23,428		$	29,512
	Amortization expense		(5,501		)	(6,084		)
	Other intangibles from business combinations		20,079			—
	Balance at end of period		$	38,006		$	23,428
	Gross carrying amount		$	80,371		$	60,292
	Accumulated amortization		(42,365		)	(36,864		)
	Net book value		$	38,006		$	23,428
Estimated future amortization expense of other intangible assets	The following presents the estimated amortization expense of other intangible assets (in thousands):
	Years ending December 31,	Amount
	2015	$	5,963
	2016	5,157
	2017	4,637
	2018	4,221
	2019	2,743
	Thereafter	15,285
		$	38,006

Deposits_Tables

Deposits (Tables)	12 Months Ended
	Dec. 31, 2014
Deposits [Abstract]
Schedule of composition of deposits	The composition of deposits was as follows (in thousands):
			December 31,
			2014		2013
	Demand deposit accounts, noninterest bearing		$	4,118,256	$	2,375,863
	NOW and money market accounts		3,913,765		2,682,419
	Savings accounts		940,345		855,394
	Certificates of deposit, $250,000 or more		838,928		522,094
	Other certificates of deposit		1,179,648		945,489
	Total		$	10,990,942	$	7,381,259
Schedule of maturities of time certificates	At December 31, 2014, the scheduled maturities of certificates of deposit were as follows (in thousands):
	2015	$	1,595,106
	2016	204,649
	2017	96,043
	2018	29,585
	2019	38,858
	Thereafter	54,335
		$	2,018,576

ShortTerm_Borrowings_Tables

Short-Term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2014
Short-term Debt [Abstract]
Summary of short-term borrowings	Short-term borrowings were as follows as of December 31, 2014 and 2013 (dollars in thousands):
		December 31,
		2014				2013
		Weighted				Weighted
		Average				Average
		Cost		Amount		Cost		Amount
	Customer repurchase agreements	0.21	%	$	219,824	0.2	%	$	193,389
	Federal Home Loan Bank advances	0.13		700,000		0.17		300,000
	Federal funds purchased	0.14		11,591		—		—
		0.15	%	$	931,415	0.18	%	$	493,389

Longterm_Borrowings_Tables

Long-term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2014
Long-term Debt, Unclassified [Abstract]
Schedule of principal payments due on long-term borrowings	The principal payments on long-term borrowings are due as follows (in thousands):
		Amount
	Years ending December 31,
	2015	$	17,589
	2016	53,147
	2017	6,018
	2018	1,917
	2019	680
	Thereafter	3,565
		$	82,916

Junior_Subordinated_Notes_Issu1

Junior Subordinated Notes Issued to Capital Trusts (Tables)	12 Months Ended
	Dec. 31, 2014
JUNIOR SUBORDINATED NOTES ISSUED TO CAPITAL TRUSTS
Outstanding junior subordinated notes and the related trust preferred securities issued by each trust	The table below summarizes the outstanding junior subordinated notes and the related trust preferred securities issued by each trust as of December 31, 2014 (in thousands):
			Coal City		MB Financial		MB Financial		MB Financial
			Capital Trust I		Capital Trust II		Capital Trust III		Capital Trust IV
	Junior Subordinated Notes:
	Principal balance		$	25,774	$	36,083	$	10,310	$	20,619
	Annual interest rate		3-mo LIBOR + 1.80%		3-mo LIBOR + 1.40%		3-mo LIBOR + 1.50%		3-mo LIBOR + 1.52%
	Stated maturity date		September 1, 2028		September 15, 2035		September 23, 2036		September 15, 2036
	Call date		September 1, 2008		December 15, 2010		September 23, 2011		September 15, 2011
	Trust Preferred Securities:
	Face Value		$	25,000	$	35,000	$	10,000	$	20,000
	Annual distribution rate		3-mo LIBOR + 1.80%		3-mo LIBOR + 1.40%		3-mo LIBOR + 1.50%		3-mo LIBOR + 1.52%
	Issuance date		July 1998		August 2005		July 2006		August 2006
	Distribution dates (1)		Quarterly		Quarterly		Quarterly		Quarterly
			MB Financial		MB Financial		FOBB		TAYC
			Capital Trust V		Capital Trust VI		Statutory Trust III (2)		Capital Trust II (3)
	Junior Subordinated Notes:
	Principal balance		$	30,928	$	23,196	$	5,155	$	41,238
	Annual interest rate		3-mo LIBOR + 1.30%		3-mo LIBOR + 1.30%		3-mo LIBOR + 2.80%		3-mo LIBOR + 2.68%
	Stated maturity date		December 15, 2037		October 30, 2037		January 23, 2034		June 17, 2034
	Call date		December 15, 2012		October 30, 2012		January 23, 2009		June 17, 2009
	Trust Preferred Securities:
	Face Value		$	30,000	$	22,500	$	5,000	$	40,000
	Annual distribution rate		3-mo LIBOR + 1.30%		3-mo LIBOR + 1.30%		3-mo LIBOR + 2.80%		3-mo LIBOR + 2.68%
	Issuance date		September 2007		October 2007		December 2003		June 2004
	Distribution dates (1)		Quarterly		Quarterly		Quarterly		Quarterly
	(1)	All distributions are cumulative and paid in cash.
	(2)	FOBB Statutory Trust III was established by First Oak Brook Bancshares, Inc. (“FOBB”) prior to the Company's acquisition of FOBB, and the junior subordinated notes issued by FOBB to FOBB Statutory Trust III were assumed by the Company upon completion of the acquisition.
	(3)	TAYC Capital Trust II was established by Taylor Capital prior to the Company's acquisition of Taylor Capital, and the junior subordinated notes issued by Taylor Capital to TAYC Capital Trust II were assumed by the Company upon completion of the acquisition. Principal balance and face value amounts associated with TAYC Capital Trust II do not include purchase accounting adjustments to such amounts, which in each case resulted in a discount of $7.5 million.

Lease_Commitments_and_Rental_E1

Lease Commitments and Rental Expense (Tables)	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Future minimum annual rental commitments for noncancelable leases and subleases	The Company leases office space for certain branch offices.  At December 31, 2014, the future minimum annual rental commitments for these noncancelable leases and subleases of such space were as follows (in thousands):
		Gross		Sublease		Net
	Years ending December 31,	Rents		Rents		Rents
	2015	$	10,272	$	797	$	9,475
	2016	8,329		484		7,845
	2017	7,398		439		6,959
	2018	5,296		414		4,882
	2019	4,680		424		4,256
	Thereafter	17,310		581		16,729
		$	53,285	$	3,139	$	50,146

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of deferred tax assets and liabilities	The deferred taxes consist of (in thousands):
		December 31,
		2014			2013
	Deferred tax asset:
	Allowance for credit losses	$	43,853		$	44,418
	Federal net operating loss carryforwards	12,234			—
	State net operating loss carryforwards	26,582			24,354
	Other real estate owned	14,229			7,878
	Stock options and restricted stock	5,904			5,816
	Loans	47,668			6,833
	Deferred compensation	10,620			8,423
	Tax credit carryforwards	25,244			13,233
	Bonus accrual	5,595			4,739
	Merger and non-compete accrual	—			623
	Other items	3,390			1,222
	Total deferred tax asset	195,319			117,539
	Valuation allowance	—			—
	Total deferred tax asset, net of valuation allowance	195,319			117,539
	Deferred tax liability:
	Equipment leasing	(112,524		)	(90,941		)
	Premises and equipment	(18,817		)	(27,059		)
	Mortgage servicing rights	(64,486		)	(7		)
	Deferred income from FDIC-assisted transactions	(45,999		)	(48,272		)
	Investment securities	(1,802		)	(5,030		)
	FHLB stock dividends	(2,652		)	(2,441		)
	Core deposit intangible	(9,118		)	(2,918		)
	Other items	(2,794		)	(3,792		)
	Total deferred tax liability	(258,192		)	(180,460		)
	Net deferred tax liability	(62,873		)	(62,921		)
	Net unrealized holding gain on investment securities available for sale	(13,099		)	(5,354		)
	Net deferred tax liability	$	(75,972	)	$	(68,275	)
Schedule of income taxes attributable to continuing operations	Income taxes attributable to continuing operations consist of (in thousands):
		Years Ended December 31,
		2014			2013			2012
	Current expense (benefit):
	Federal	$	25,270		$	12,234		$	15,075
	State	11,971			5,576			6,225
	Foreign	—			—			—
		37,241			17,810			21,300
	Deferred expense (benefit):
	Federal	3,122			17,245			13,688
	State	(3,170		)	4,436			1,489
	Foreign	—			—			—
		(48		)	21,681			15,177
		$	37,193		$	39,491		$	36,477
Schedule of reconciliation between the statutory federal income tax rate and the effective tax rate on income from continuing operations	The reconciliation between the statutory federal income tax rate of 35% and the effective tax rate on income from continuing operations follows (in thousands):
		Years Ended December 31,
		2014			2013			2012
	Federal income tax expense at expected statutory rate	$	43,153		$	48,281		$	44,398
	Increase (decrease) due to:
	Tax exempt income, net	(14,848		)	(14,200		)	(12,539		)
	State tax expense net of federal impact	5,721			6,508			5,014
	Non-deductible contingent consideration	3,738			—			—
	Non-includable increase in cash surrender value of life insurance	(1,120		)	(1,111		)	(1,177		)
	Non-deductible merger expense	988			591			—
	Adjustment of tax contingency reserves	(31		)	(24		)	14
	Other items, net	(408		)	(554		)	767
	Income tax expense	$	37,193		$	39,491		$	36,477
Schedule of reconciliation of the change in unrecognized tax benefits	A reconciliation of the change in unrecognized tax benefits from January 1, 2014 to December 31, 2014 is as follows (in thousands):
		Unrecognized Tax Benefit			Interest on unrecognized			Total Unrecognized Tax
		Without Interest			Tax Benefit			Benefit Including Interest
	Balance at January 1, 2014	$	73		$	7		$	80
	Increases for tax positions of prior years	—			6			6
	Acquisition related increases	939			—			939
	Benefits recognized	(31		)	(6		)	(37		)
	Balance at December 31, 2014	$	981		$	7		$	988

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of outstanding financial instruments, contractual amounts of off-balance sheet credit risk	At December 31, 2014 and 2013, the following financial instruments were outstanding, the contractual amounts of which represent off-balance sheet credit risk (in thousands):
		Contractual Amount
		2014		2013
	Commitments to extend credit:
	Home equity lines	$	221,102	$	208,581
	Other commitments	2,643,220		1,214,391
	Letters of credit:
	Standby	131,810		69,556
	Commercial	2,401		708

Regulatory_Matters_Tables

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2014
Banking and Thrift [Abstract]
Schedule of the required and actual amounts and ratios for the Company and its subsidiary bank	The required and actual amounts and ratios for the Company and its bank subsidiary are presented below as of the dates indicated (dollars in thousands):
										To Be Well
										Capitalized Under
						For Capital				Prompt Corrective
		Actual				Adequacy Purposes				Action Provisions
		Amount		Ratio		Amount		Ratio		Amount		Ratio
	As of December 31, 2014
	Total capital (to risk-weighted assets):
	Consolidated	$	1,544,759	13.62	%	$	907,369	8	%	N/A		N/A
	MB Financial Bank	1,473,928		13.03		904,917		8		$	1,131,146	10	%
	Tier 1 capital (to risk-weighted assets):
	Consolidated	1,430,702		12.61	%	453,684		4	%	N/A		N/A
	MB Financial Bank	1,359,871		12.02		452,459		4		678,688		6	%
	Tier 1 capital (to average assets):
	Consolidated	1,430,702		10.47	%	546,766		4	%	N/A		N/A
	MB Financial Bank	1,359,871		9.96		545,943		4		682,429		5	%
	As of December 31, 2013
	Total capital (to risk-weighted assets):
	Consolidated	$	1,106,541	16.53	%	$	535,430	8	%	N/A		N/A
	MB Financial Bank	974,189		14.59		534,004		8		$	667,505	10	%
	Tier 1 capital (to risk-weighted assets):
	Consolidated	1,022,512		15.28	%	267,715		4	%	N/A		N/A
	MB Financial Bank	890,380		13.34		267,002		4		400,503		6	%
	Tier 1 capital (to average assets):
	Consolidated	1,022,512		11.22	%	364,587		4	%	N/A		N/A
	MB Financial Bank	890,380		9.79		363,904		4		454,880		5	%
	N/A — not applicable

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Financial assets and financial liabilities measured at fair value on a recurring basis	The following table summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2014 and 2013, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands):
			Total				Quoted Prices in				Significant Other				Significant
							Active Markets for				Observable Inputs				Unobservable Inputs
							Identical Assets				(Level 2)				(Level 3)
							(Level 1)
	2014
	Financial assets
	Securities available for sale:
	U.S. Government sponsored agencies and enterprises		$	65,873			$	—			$	65,873			$	—
	States and political subdivisions		410,854				—				410,391				463
	Residential mortgage-backed securities		720,563				—				720,053				510
	Commercial mortgage-backed securities		187,662				—				187,662				—
	Corporate bonds		259,203				—				259,203				—
	Equity securities		10,597				10,597				—				—
	Loans held for sale		737,209				—				737,209				—
	Mortgage servicing rights		235,402				—				—				235,402
	Assets held in trust for deferred compensation		16,829				16,829				—				—
	Derivative financial instruments		46,388				1,607				39,707				5,074
	Financial liabilities
	Other liabilities (1)		16,483				16,483				—				—
	Derivative financial instruments		40,499				7,209				33,290				—
	2013
	Financial assets
	Securities available for sale:
	U.S. Government sponsored agencies and enterprises		$	52,068			$	—			$	52,068			$	—
	States and political subdivisions		19,143				—				19,143				—
	Residential mortgage-backed securities		701,233				—				700,542				691
	Commercial mortgage-backed securities		52,941				—				52,941				—
	Corporate bonds		283,070				—				277,905				5,165
	Equity securities		10,457				10,457				—				—
	Loans held for sale		629				—				629				—
	Assets held in trust for deferred compensation		10,679				10,679				—				—
	Derivative financial instruments		18,645				—				18,645				—
	Financial liabilities
	Other liabilities (1)		10,569				10,569				—				—
	Derivative financial instruments		18,632				—				18,632				—
	(1) Liabilities associated with assets held in trust for deferred compensation
Financial assets measured at fair value on a recurring and non-recurring basis, unobservable inputs used	The following table presents additional information about the unobservable inputs used in the fair value measurement of financial assets measured on a nonrecurring basis that were categorized within the Level 3 of the fair value hierarchy (fair value in thousands):
		Fair Value at				Valuation
		December 31, 2014				Technique		Unobservable Input		Range
	Impaired loans	$	61,717			Appraisal of collateral		Appraisal adjustments - sales costs		5% - 10%
	Foreclosed assets	38,619				Appraisal of collateral		Appraisal adjustments - sales costs		5% - 10%
	The following table presents additional information about the unobservable inputs used in the fair value measurement of financial assets measured on a recurring basis that were categorized within the Level 3 of the fair value hierarchy (fair value in thousands):
		Fair Value at
		December 31, 2014				Valuation Technique		Unobservable Input		Range
		(in thousands)
	States and political subdivisions	$	463			Discounted cash flows		Credit assumption		45% Loss
	Residential mortgage-backed securities	510				Discounted cash flows		Constant pre-payment rates (CPR)		1% - 3%
	Mortgage servicing rights	235,402				Discounted cash flows		CPR		4.9% - 26.9%
								Discount rate		9.25 - 16.00
								Maturity (months)		36 - 460
								Delinquencies		0.00 - 28.57
								Costs to service		$ 60 - $ 356
	Derivative financial instruments (mortgage	5,074				Sales cash flows		Expected closing ratio		16.90% - 94.00%
	interest rate lock commitments)							Expected delivery price		98.89 bps - 110.01 bps
Schedule of sensitivity analysis of fair value, transferor's interests in transferred financial assets	Key economic assumptions used in the measuring of the fair value of the mortgage servicing rights and the sensitivity of the fair value to immediate adverse changes in those assumptions at December 31, 2014 are presented in the following table. This table does not take into account the derivatives used to economically hedge the mortgage servicing rights.
	(dollars in thousands, except for weighted average cost to service)	December 31, 2014
	Weighted average prepayment speed (CPR)	11.5		%
	Impact on fair value of 10% adverse change	$	(9,650	)
	Impact on fair value of 20% adverse change	(18,574		)
	Weighted average discount rate	9.41		%
	Impact on fair value of 10% adverse change	$	(8,998	)
	Impact on fair value of 20% adverse change	(17,356		)
	Weighted average delinquency rate	1.25		%
	Impact on fair value of 10% adverse change	$	(1,520	)
	Impact on fair value of 20% adverse change	(2,196		)
	Weighted average costs to service	$	70
	Impact on fair value of 10% adverse change	(3,325		)
	Impact on fair value of 20% adverse change	(6,651		)
Financial assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3)	The following table presents additional information about financial assets measured at fair value on a recurring basis for which the Company used significant unobservable inputs (Level 3) (in thousands):
			Year Ended
			December 31,
			2014				2013				2014				2013			2014			2013
			Investment Securities								Mortgage Servicing Rights							Derivatives
	Balance, beginning of period		$	5,856			$	6,071			$	—			$	—		$	—		$	—
	Acquired through business combination		507				—				224,798				—			5,922			—
	Purchases		—				—				1,096				—			—			—
	Originations		—				—				21,285				—			—			—
	Other comprehensive income		128				(44		)		(11,777		)		—			(848		)	—
	Principal payments		(363		)		(157		)		—				—			—			—
	Impairment charge		(92		)		(14		)		—				—			—			—
	Sales		(498		)		—				—				—			—			—
	Transferred out of level 3		(4,565		)		—				—				—			—			—
	Balance, ending of period		$	973			$	5,856			$	235,402			$	—		$	5,074		$	—
Assets measured at fair value on a nonrecurring basis	Assets measured at fair value on a nonrecurring basis as of December 31, 2014 and 2013 are included in the table below (in thousands):
			Total				Quoted Prices in Active				Significant Other				Significant
							Markets for Identical				Observable Inputs				Unobservable Inputs
							Assets (Level 1)				(Level 2)				(Level 3)
	2014
	Financial assets:
	Impaired loans		$	61,717			$	—			$	—			$	61,717
	Non-financial assets:
	Foreclosed assets		38,619				—				—				38,619
	2013
	Financial assets:
	Impaired loans		$	77,497			$	—			$	—			$	77,497
	Non-financial assets:
	Foreclosed assets		44,601				—				—				44,601
Estimated fair values of financial instruments	The estimated fair values of financial instruments are as follows (in thousands):
			December 31, 2014
			Carrying Amount				Estimated Fair Value			Quoted Prices in Active			Significant Other			Significant
										Markets for Identical			Observable Inputs			Unobservable Inputs
										Assets (Level 1)			(Level 2)			(Level 3)
	Financial Assets:
	Cash and due from banks		$	256,804			$	256,804		$	256,804		$	—		$	—
	Interest bearing deposits with banks		55,277				55,277			55,277			—			—
	Investment securities available for sale		1,654,752				1,654,752			10,597			1,643,182			973
	Investment securities held to maturity		993,380				1,035,061			—			1,035,061			—
	Non-marketable securities - FHLB and FRB stock		75,569				75,569			—			—			75,569
	Loans held for sale		737,209				737,209			—			737,209			—
	Loans, net		8,973,191				8,956,494			—			—			8,956,494
	Accrued interest receivable		49,065				49,065			49,065			—			—
	Derivative financial instruments		46,388				46,388			1,607			39,707			5,074
	Financial Liabilities:
	Non-interest bearing deposits		$	4,118,256			$	4,118,256		$	4,118,256		$	—		$	—
	Interest bearing deposits		6,872,686				6,877,349			—			—			6,877,349
	Short-term borrowings		931,415				931,416			—			—			931,416
	Long-term borrowings		82,916				86,025			—			—			86,025
	Junior subordinated notes issued to capital trusts		185,778				122,408			—			—			122,408
	Accrued interest payable		3,709				3,709			3,709			—			—
	Derivative financial instruments		40,499				40,499			7,209			33,290			—
			December 31, 2013
			Carrying Amount				Estimated Fair Value			Quoted Prices in Active			Significant Other			Significant
										Markets for Identical			Observable Inputs			Unobservable Inputs
										Assets (Level 1)			(Level 2)			(Level 3)
	Financial Assets:
	Cash and due from banks		$	205,193			$	205,193		$	205,193		$	—		$	—
	Interest bearing deposits with banks		268,266				268,266			268,266			—			—
	Federal funds sold		42,950				42,950			42,950			—			—
	Investment securities available for sale		1,118,912				1,118,912			10,457			1,102,599			5,856
	Investment securities held to maturity		1,182,533				1,198,929			—			1,198,929			—
	Non-marketable securities - FHLB and FRB stock		51,417				51,417			—			—			51,417
	Loans held for sale		629				629			—			629			—
	Loans, net		5,600,805				5,583,759			—			—			5,583,759
	Accrued interest receivable		36,593				36,593			36,593			—			—
	Derivative financial instruments		18,645				18,645			—			18,645			—
	Financial Liabilities:
	Non-interest bearing deposits		$	2,375,863			$	2,375,863		$	2,375,863		$	—		$	—
	Interest bearing deposits		5,005,396				5,012,928			—			—			5,012,928
	Short-term borrowings		493,389				493,384			—			—			493,384
	Long-term borrowings		62,159				66,301			—			—			66,301
	Junior subordinated notes issued to capital trusts		152,065				101,247			—			—			101,247
	Accrued interest payable		2,042				2,042			2,042			—			—
	Derivative financial instruments		18,632				18,632			—			18,632			—

Stock_Incentive_Plans_Tables

Stock Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of the impact of share-based payment plans in the financial statements	The following table summarizes the impact of the Company’s share-based payment plans in the financial statements for the periods shown (in thousands):
		Year Ended December 31,
		2014				2013				2012
	Total cost of share-based payment plans during the year	$	8,974			$	5,456			$	4,806
	Amount of related income tax benefit recognized in income	$	3,528			$	2,159			$	1,918
Additional information related to options outstanding	The following table summarizes stock options outstanding for the year ended December 31, 2014:
		Number of			Weighted				Weighted		Aggregate
		Options			Average				Average		Intrinsic
					Exercise				Remaining		Value
					Price				Contractual		(in thousands)
									Term
									(in years)
	Options outstanding as of December 31, 2013	2,443,752			$	27.57			4.71
	Granted	231,977			29.63
	Exercised	(211,339	)		19.88
	Expired or cancelled	(177,125	)		35.78
	Forfeited	(36,551	)		22.33
	Options outstanding as of December 31, 2014	2,250,714			$	27.94			4.39		$	13,820
	Options exercisable as of December 31, 2014	1,689,055			$	29			3.2		$	9,263
Assumptions used for options granted	The following assumptions were used for options granted during the years ended December 31, 2014, 2013, and 2012:
		For the Years Ended December 31,
		2014				2013				2012
	Risk-free interest rate	1.82		%		1.92		%		1.02		%
	Expected volatility of Company’s stock	23.16		%		25.18		%		27.17		%
	Expected dividend yield	1.65		%		1.73		%		2		%
	Expected life of options (years)	5.5				5.6				5.7
	Weighted average fair value per option of options granted during the year	$	5.93			$	5.88			$	4.23
Summary of changes in restricted shares	The following is a summary of changes in restricted shares and units for the year ended December 31, 2014:
		Number of			Weighted
		Shares			Average
					Grant Date
					Fair Value
	Shares and Units Outstanding at December 31, 2013	685,719			$	22.59
	Granted	443,375			29.23
	Vested	(305,504	)		20.53
	Forfeited	(22,505	)		24.92
	Shares and Units Outstanding at December 31, 2014	801,085			$	26.99

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of derivative financial instruments	The Company’s derivative financial instruments are summarized below as of December 31, 2014 and 2013 (in thousands):
		Asset Derivatives											Liability Derivatives
		December 31, 2014						December 31, 2013					December 31, 2014					December 31, 2013
		Notional			Estimated			Notional			Estimated		Notional		Estimated			Notional			Estimated
		Amount			Fair Value			Amount			Fair Value		Amount		Fair Value			Amount			Fair Value
	Derivative instruments designated as hedges of fair value:
	Interest rate swap contracts (1)	$	—		$	—		$	—		$	—	$	197	$	(15	)	$	238		$	(23	)
	Stand-alone derivative instruments: (2)
	Interest rate swap contracts	1,509,930			37,039			550,883			17,298		2,001,787		(30,761		)	551,798			(17,350		)
	Interest rate options contracts	55,830			283			83,907			323		55,830		(283		)	84,953			(323		)
	Foreign exchange contracts	27,402			2,276			31,361			1,006		27,002		(2,109		)	47,760			(935		)
	Spot foreign exchange contracts	512			5			—			—		304		(18		)	—			—
	Mortgage related derivatives	871,446			6,785			1,783			18		879,841		(7,313		)	250			(1		)
	Total non-hedging derivative instruments	2,465,120			46,388			667,934			18,645		2,964,764		(40,484		)	684,761			(18,609		)
	Total	$	2,465,120		$	46,388		$	667,934		$	18,645	$	2,964,961	$	(40,499	)	$	684,999		$	(18,632	)
	(1) Hedged fixed-rate commercial real estate loans
	(2) These portfolio swaps are not designated as hedging instruments under ASC Topic 815.
Schedule of the amount of gains and losses on derivative contracts designated as hedges and not designated as hedges	Amounts included in the other income in the consolidated statements of operations related to derivative financial instruments were as follows (in thousands):
		Years Ended
		December 31,
		2014			2013			2012
	Derivative instruments designated as hedges of fair value:
	Interest rate swap contracts	$	8		$	9		$	(15	)
	Stand-alone derivative instruments:
	Interest rate swap contracts	2,458			40			30
	Interest rate options contracts	—			—			—
	Foreign exchange contracts	96			(30		)	67
	Spot foreign exchange contracts	(14		)	—			—
	Mortgage related derivatives	(965		)	(109		)	96
	Total non-hedging derivative instruments	1,575			(99		)	193
	Total	$	1,583		$	(90	)	$	178
Schedule of derivative instruments	Information about the Company's financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2014 is summarized below (in thousands):
		Financial Assets									Financial Liabilities
		Gross Amount Recognized			Gross Amount Offset			Net Amount Recognized			Gross Amount Recognized		Gross Amount Offset		Net Amount Recognized
	Derivatives:
	Interest rate swaps, caps and floors	$	10,727		$	—		$	10,727		$	29,916	$	—	$	29,916
	Foreign currency forward contracts	1,525			—			1,525			709		—		709
	Mortgage banking derivatives	1,700			—			1,700			7,302		—		7,302
	Total derivatives	13,952			—			13,952			37,927		—		37,927
	Repurchase agreements	—			—			—			219,824		—		219,824
	Total	$	13,952		$	—		$	13,952		$	257,751	$	—	$	257,751
		Financial Assets											Financial Liabilities
		Net Amount Recognized			Financial Instruments			Collateral			Net Amount		Net Amount Recognized		Financial Instruments			Collateral			Net Amount
	Derivatives:
	Counterparty A	$	13		$	(13	)	$	—		$	—	$	9,556	$	(13	)	$	(9,543	)	$	—
	Counterparty B	145			(145		)	—			—		3,736		(145		)	(3,591		)	—
	Counterparty C	6,123			(6,123		)	—			—		10,335		(6,122		)	(4,213		)	—
	Other counterparties	7,671			(3,920		)	—			3,751		14,300		(3,920		)	(8,663		)	1,717
	Total derivatives	13,952			(10,201		)	—			3,751		37,927		(10,200		)	(26,010		)	1,717
	Repurchase agreements	—			—			—			—		219,824		—			(219,824		)	—
	Total	$	13,952		$	(10,201	)	$	—		$	3,751	$	257,751	$	(10,200	)	$	(245,834	)	$	1,717
	Information about the Company's financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2013 is summarized below (in thousands):
		Financial Assets									Financial Liabilities
		Gross Amount Recognized			Gross Amount Offset			Net Amount Recognized			Gross Amount Recognized		Gross Amount Offset		Net Amount Recognized
	Derivatives:
	Interest rate swaps, caps and floors	$	5,792		$	—		$	5,792		$	11,904	$	—	$	11,904
	Foreign currency forward contracts	80			—			80			848		—		848
	Mortgage banking derivatives	3			—			3			1		—		1
	Total derivatives	5,875			—			5,875			12,753		—		12,753
	Repurchase agreements	—			—			—			193,389		—		193,389
	Total	$	5,875		$	—		$	5,875		$	206,142	$	—	$	206,142
		Financial Assets											Financial Liabilities
		Net Amount Recognized			Financial Instruments			Collateral			Net Amount		Net Amount Recognized		Financial Instruments			Collateral			Net Amount
	Derivatives:
	Counterparty A	$	883		$	(883	)	$	—		$	—	$	10,669	$	(883	)	$	(9,786	)	$	—
	Counterparty B	1,836			(412		)	—			1,424		412		(412		)	—			—
	Counterparty C	2,380			(1,612		)	—			768		1,612		(1,612		)	—			—
	Other counterparties	776			(5		)	—			771		60		(5		)	—			55
	Total derivatives	5,875			(2,912		)	—			2,963		12,753		(2,912		)	(9,786		)	55
	Repurchase agreements	—			—			—			—		193,389		—			(193,389		)	—
	Total	$	5,875		$	(2,912	)	$	—		$	2,963	$	206,142	$	(2,912	)	$	(203,175	)	$	55

Operating_Segments_Tables

Operating Segments (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Schedule of segment reporting information, by segment	The following table presents summary financial information for the reportable segments (in thousands):
		Banking			Leasing		Mortgage Banking			Consolidated
	Year ended December 31,
	2014
	Net interest income	$	328,326		$	12,783	$	9,714		$	350,823
	Provision for credit losses	12,022			35		(5		)	12,052
	Non-interest income	115,411			59,806		46,088			221,305
	Non-interest expense (1)	350,358			39,525		46,899			436,782
	Income tax expense	21,106			12,524		3,563			37,193
	Net income	$	60,251		$	20,505	$	5,345		$	86,101
	Total assets	$	12,698,740		$	930,748	$	972,611		$	14,602,099
	Year ended December 31,
	2013
	Net interest income	$	267,131		$	5,205	$	—		$	272,336
	Provision for credit losses	(6,167		)	363		—			(5,804		)
	Non-interest income	92,936			59,794		1,664			154,394
	Non-interest expense (1)	259,753			34,835		—			294,588
	Income tax expense	28,201			11,290		—			39,491
	Net income	$	78,280		$	18,511	$	1,664		$	98,455
	Total assets	$	9,167,127		$	474,300	$	—		$	9,641,427
	Year ended December 31,
	2012
	Net interest income	$	290,881		$	1,907	$	—		$	292,788
	Provision for credit losses	(9,035		)	135		—			(8,900		)
	Non-interest income	93,124			33,744		2,325			129,193
	Non-interest expense	284,452			19,578		—			304,030
	Income tax expense	30,780			5,697		—			36,477
	Net income	$	77,808		$	10,241	$	2,325		$	90,374
	Total assets	$	9,187,480		$	384,325	$	—		$	9,571,805
	(1)	Includes merger related expenses of $34.8 million and $2.5 million in the banking segment for the years ended December 31, 2014 and 2013, respectively. Also, includes contingent consideration expense related to our acquisition of Celtic Leasing Corp. in the banking segment for the year ended December 31, 2014.

Condensed_Parent_Company_Finan1

Condensed Parent Company Financial Information (Tables)	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed balance sheets	Balance Sheets
	(In thousands)
		December 31,
		2014			2013
	Assets
	Cash	$	32,161		$	122,001
	Investments in subsidiaries	2,143,408			1,340,641
	Other assets	38,941			24,505
	Total assets	$	2,214,510		$	1,487,147
	Liabilities and Stockholders’ Equity
	Junior subordinated notes issued to capital trusts	$	185,778		$	152,065
	Other liabilities	446			8,400
	Stockholders’ equity	2,028,286			1,326,682
	Total liabilities and stockholders’ equity	$	2,214,510		$	1,487,147
Condensed statements of income	Statements of Operations
	(In thousands)
		Years Ended December 31,
		2014			2013			2012
	Dividends from subsidiaries	$	101,500		$	80,500		$	146,000
	Interest and other income	3,097			4,215			1,682
	Interest and other expense	14,636			7,143			7,117
	Income before income tax benefit and equity in undistributed net income of subsidiaries	89,961			77,572			140,565
	Income tax benefit	(4,590		)	(1,223		)	(2,192		)
	Income before equity in undistributed net income of subsidiaries	94,551			78,795			142,757
	Equity in undistributed net (loss) income of subsidiaries	(8,450		)	19,660			(52,383		)
	Net income	86,101			98,455			90,374
	Dividends and discount accretion on preferred shares	4,000			—			3,269
	Net income available to common stockholders	$	82,101		$	98,455		$	87,105
Condensed statements of cash flows	Statements of Cash Flows
	(In thousands)
		Years Ended December 31,
		2014			2013			2012
	Cash Flows From Operating Activities
	Net income	$	86,101		$	98,455		$	90,374
	Adjustments to reconcile net income to net cash provided by operating activities:
	Compensation expense for share-based payment plans	8,974			5,456			4,806
	Equity in undistributed net income of subsidiaries	8,450			(19,660		)	52,383
	Change in other assets and other liabilities	(8,980		)	(1,460		)	(5,064		)
	Net cash provided by operating activities	94,545			82,791			142,499
	Cash Flows From Investing Activities
	Net decrease in loans	—			6,960			21,010
	Net cash paid in business acquisition	(101,546		)	—			—
	Net cash (used in) provided by investing activities	(101,546		)	6,960			21,010
	Cash Flows From Financing Activities
	Treasury stock transactions, net	(2,690		)	(1,672		)	(249		)
	Stock options exercised	1,034			1,014			154
	Excess tax benefits from share-based payment arrangements	396			(325		)	(390		)
	Dividends paid on common stock	(34,210		)	(24,070		)	(7,101		)
	Dividends paid on preferred stock	(2,000		)	—			(3,239		)
	Repurchase of preferred stock and warrant	—			—			(197,518		)
	Redemption of on junior subordinated notes issued to capital trusts	(45,369		)	—			(6,186		)
	Net cash used in financing activities	(82,839		)	(25,053		)	(214,529		)
	Net (decrease) increase in cash	(89,840		)	64,698			(51,020		)
	Cash:
	Beginning of year	122,001			57,303			108,323
	End of year	$	32,161		$	122,001		$	57,303

Significant_Accounting_Policie3

Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2014
	category
	element
	rating
	indicator
	instrument
Troubled debt restructurings:
Number of notes into which a note is restructured (in instruments)	2
Allowance for loan and lease losses:
Number of elements in allowance for loan losses	3
Number of categories of commercial related loans for which a general loan loss reserve	4
Loan risk rating that represents those loans least likely to default	1
Loan risk rating that represents a loss	9
Period of loan risk rating migration (in years)	14 years
Period for computing average losses (in years)	13 years
Number of indicators for which correlation to charge-offs is tested	20
Time horizon over which forecast is applied (in years)	1 year
Minimum
Loans and leases:
Period past due for discontinuance of interest accrual on loans (in days)	90 days
Troubled debt restructurings:
Period of sustained repayment for a note to get accrual status (in months)	6 months
Finite-Lived Intangible Assets, Net [Abstract]
Finite-lived intangible assets, useful life	4 years
Maximum
Cash and cash equivalents:
Term of original maturity to classify instrument as cash equivalent (in days)	90 days
Allowance for loan and lease losses:
Period in which external appraisal on real estate secured impaired loan was obtained (in months)	12 months
Lease investments:
Life of leased equipment under operating leases (in years)	5 years
Finite-Lived Intangible Assets, Net [Abstract]
Finite-lived intangible assets, useful life	15 years
MB Financial Bank
Significant Accounting Policies
Number of wholly owned subsidiaries	3
ILLINOIS | MB Financial Bank
Significant Accounting Policies
Number of banking offices	86

Significant_Accounting_Policie4

Significant Accounting Policies (Details 2)	12 Months Ended
	Dec. 31, 2014
Land improvements
Premises and Equipment
Estimated useful life (in years)	15 years
Minimum | Computer equipment and software
Premises and Equipment
Estimated useful life (in years)	3 years
Minimum | Software
Premises and Equipment
Estimated useful life (in years)	3 years
Minimum | Furniture and equipment
Premises and Equipment
Estimated useful life (in years)	5 years
Minimum | Buildings and building improvements
Premises and Equipment
Estimated useful life (in years)	5 years
Maximum | Computer equipment and software
Premises and Equipment
Estimated useful life (in years)	7 years
Maximum | Software
Premises and Equipment
Estimated useful life (in years)	7 years
Maximum | Furniture and equipment
Premises and Equipment
Estimated useful life (in years)	10 years
Maximum | Buildings and building improvements
Premises and Equipment
Estimated useful life (in years)	39 years

Significant_Accounting_Policie5

Significant Accounting Policies (Details 3) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	segment
Basic and diluted earnings per common share:
Net income	$86,101	$98,455	$90,374
Less: preferred stock dividends and discount accretion	4,000		3,269
Net income available to common stockholders	82,101	98,455	87,105
Earnings allocated to common stockholders	82,099	98,453	87,102
Weighted average shares outstanding for basic earnings per common share	62,012,196	54,509,612	54,270,297
Weighted average shares outstanding for diluted earnings per common share	62,573,406	54,993,865	54,505,976
Basic earnings per common share (dollars per share)	$1.32	$1.81	$1.61
Diluted earnings per common share (dollars per share)	$1.31	$1.79	$1.60
Segment Reporting
Number of reportable segments	3
Common Stock
Basic and diluted earnings per common share:
Distributed earnings allocated to common stock	34,422	24,290	7,149
Undistributed earnings	51,679	74,165	83,225
Net income	86,101	98,455	90,374
Net income available to common stockholders	82,101	98,455	87,105
Weighted average shares outstanding for basic earnings per common share	62,012,196	54,509,612	54,270,297
Dilutive effect of equity awards	561,210	484,253	235,679
Weighted average shares outstanding for diluted earnings per common share	62,573,406	54,993,865	54,505,976
Participating Securities
Basic and diluted earnings per common share:
Less: earnings and dividends allocated to participating securities	$2	$2	$3

Business_Combinations_Details

Business Combinations (Details) (USD $)	12 Months Ended	0 Months Ended	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Aug. 18, 2014	Dec. 31, 2013	Aug. 15, 2014
Business combination
Preferred stock, par value	$0.01		$0.01
Assets
Goodwill	$711,521,000		$423,369,000
LIABILITIES
Series A preferred stock at $28.82 per share at August 15, 2014	115,280,000		0
Decrease in fair value of loans acquired	-7,100,000
Decrease in fair value of core deposit intangibles acquired	-4,900,000
Decrease in fair value of mortgage servicing rights acquired	-8,000,000
Taylor Capital Group, Inc.
Business combination
Amount called by each warrant or right		4.08
Payments to acquire businesses, employee stock options and warrants		4,400,000
Assets
Cash and cash equivalents		154,684,000
Investment securities available for sale		826,691,000
Investment securities held to maturity		22,599,000
Non-marketable securities - FRB and FHLB Stock		50,620,000
Loans held for sale		670,671,000
Loans		3,532,211,000
Leases investments, net		11,885,000
Premises and equipment		19,701,000
Goodwill		288,152,000
Core deposit intangible		20,079,000
Mortgage servicing rights		224,453,000
Other real estate owned		4,720,000
Other assets		130,478,000
Total assets		5,956,944,000
LIABILITIES
Deposits		3,953,213,000
Short-term borrowings		1,035,800,000
Junior subordinated notes issued to capital trusts		80,843,000
Accrued expenses and other liabilities		123,028,000
Total liabilities		5,192,884,000
Total identifiable net assets less Series A preferred stock		648,780,000
Market value of common stock at $26.49 per share at August 15, 2014 (19,602,482 shares of common stock issued)		519,270,000
Cash paid		129,510,000
Total fair value of consideration, excluding Series A preferred stock		648,780,000
PCI Loans
Fair value of acquired loans		3,532,211,000
Non-PCI Loans
Business combination, merger expenses	34,800,000		2,500,000
Business combination, professional and legal fees	7,100,000		2,400,000
Business Acquisition, Pro Forma Information [Abstract]
Business acquisition, pro forma revenue	774,778,000		790,655,000
Business acquisition, pro forma net income (loss)	112,220,000		180,085,000
Common Stock | Taylor Capital Group, Inc.
Business combination
Number of securities called by each warrant or right		0.64318
Business acquisition, shares of common stock issued		19,600,000		19,602,482
LIABILITIES
Share Price				$26.49
Restricted stock | Taylor Capital Group, Inc.
LIABILITIES
Cash paid		3,700,000
Series A Preferred Stock | Taylor Capital Group, Inc.
Business combination
Preferred stock, par value				$28.82
LIABILITIES
Series A preferred stock at $28.82 per share at August 15, 2014		115,280,000
Substandard | Taylor Capital Group, Inc.
Assets
Loans		204,805,000
PCI Loans
Contractually required principal and interest payments		244,650,000
Nonaccretable difference		-34,219,000
Cash flows expected to be collected		210,431,000
Accretable difference		-5,626,000
Fair value of acquired loans		204,805,000
Pass | Taylor Capital Group, Inc.
Non-PCI Loans
Contractually required principal and interest payments		3,707,463,000
Contractually required interest payments not expected to be collected due to estimated prepayments		-302,329,000
Cash flows expected to be collected		3,405,134,000
Accretable difference		-77,728,000
Fair value of acquired loans		$3,327,406,000

Restrictions_on_Cash_and_Due_F1

Restrictions on Cash and Due From Banks (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Restrictions on Cash and Due from Banks [Abstract]
Required reserve balances in cash or on deposits with Federal Reserve Bank	$127.20	$75.10

Investment_Securities_Details

Investment Securities (Details) (USD $)	12 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Dec. 31, 2014
Available for Sale
Amortized Cost	$1,111,922,000			$1,624,268,000
Gross Unrealized Gains	13,928,000			35,370,000
Gross Unrealized Losses	-6,938,000			-4,886,000
Fair Value	1,118,912,000			1,654,752,000
Held to Maturity
Amortized Cost	1,182,533,000			993,380,000
Gross Unrealized Gains	20,762,000			42,063,000
Gross Unrealized Losses	-4,366,000			-382,000
Investment Securities held to maturity	1,198,929,000			1,035,061,000
Total Available for Sale and Held to Maturity Investment Securities
Amortized Cost	2,294,455,000			2,617,648,000
Gross Unrealized Gains	34,690,000			77,433,000
Gross Unrealized Losses	-11,304,000			-5,268,000
Fair Value	2,317,841,000			2,689,813,000
Transfer of investment securities held to maturity to investment securities available for sale	0	0
U.S. Government sponsored agencies and enterprises
Available for Sale
Amortized Cost	50,486,000			64,612,000
Gross Unrealized Gains	1,704,000			1,281,000
Gross Unrealized Losses	-122,000			-20,000
Fair Value	52,068,000			65,873,000
States and political subdivisions
Available for Sale
Amortized Cost	19,398,000			390,076,000
Gross Unrealized Gains	22,000			20,846,000
Gross Unrealized Losses	-277,000			-68,000
Fair Value	19,143,000			410,854,000
Held to Maturity
Amortized Cost	932,955,000			752,558,000
Gross Unrealized Gains	7,584,000			30,089,000
Gross Unrealized Losses	-4,366,000			-382,000
Investment Securities held to maturity	936,173,000			782,265,000
Total Available for Sale and Held to Maturity Investment Securities
Percentage of securities consisting general obligation issues				93.00%
Transferred security at fair value			291,200,000
Transfer of investment securities held to maturity to investment securities available for sale			273,500,000
Held-to-maturity securities, realized loss			3,200,000
Residential mortgage-backed securities
Available for Sale
Amortized Cost	696,415,000			713,413,000
Gross Unrealized Gains	8,555,000			8,977,000
Gross Unrealized Losses	-3,737,000			-1,827,000
Fair Value	701,233,000			720,563,000
Held to Maturity
Amortized Cost	249,578,000			240,822,000
Gross Unrealized Gains	13,178,000			11,974,000
Gross Unrealized Losses	0			0
Investment Securities held to maturity	262,756,000			252,796,000
Commercial mortgage-backed securities
Available for Sale
Amortized Cost	50,891,000			186,110,000
Gross Unrealized Gains	2,050,000			1,772,000
Gross Unrealized Losses	0			-220,000
Fair Value	52,941,000			187,662,000
Corporate bonds
Available for Sale
Amortized Cost	284,083,000			259,526,000
Gross Unrealized Gains	1,597,000			2,428,000
Gross Unrealized Losses	-2,610,000			-2,751,000
Fair Value	283,070,000			259,203,000
Equity securities
Available for Sale
Amortized Cost	10,649,000			10,531,000
Gross Unrealized Gains	0			66,000
Gross Unrealized Losses	-192,000			0
Fair Value	10,457,000			10,597,000
Certain longer-term and lower-coupon investment securities
Available for Sale
Fair Value			$451,600,000
Geographic Concentration Risk | States and political subdivisions | Securities Portfolio
Total Available for Sale and Held to Maturity Investment Securities
Percentage of investments issued by states and political subdivisions that were within the state of Illinois				27.00%

Investment_Securities_Details_

Investment Securities (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	securitypositions	securitypositions
Available for Sale
Less Than 12 Months, Fair Value	$405,448	$386,481
Less Than 12 Months, Unrealized Losses	-2,756	-5,991
12 Months or More, Fair Value	42,606	49,635
12 Months or More, Unrealized Losses	-2,130	-947
Total Fair Value	448,054	436,116
Total Unrealized Losses	-4,886	-6,938
Total
Less Than 12 Months, Fair Value	434,234	621,497
Less Than 12 Months, Unrealized Losses	-2,886	-10,321
12 Months or More, Fair Value	56,844	50,936
12 Months or More, Unrealized Losses	-2,382	-983
Total Fair Value	491,078	672,433
Total Unrealized Losses	-5,268	-11,304
Number of security positions in the investment portfolio in an unrealized loss position	168	345
U.S. Government sponsored agencies and enterprises
Available for Sale
Less Than 12 Months, Fair Value	9,644	18,598
Less Than 12 Months, Unrealized Losses	-20	-122
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Total Fair Value	9,644	18,598
Total Unrealized Losses	-20	-122
States and political subdivisions
Available for Sale
Less Than 12 Months, Fair Value	7,784	2,275
Less Than 12 Months, Unrealized Losses	-21	-166
12 Months or More, Fair Value	3,558	4,748
12 Months or More, Unrealized Losses	-47	-111
Total Fair Value	11,342	7,023
Total Unrealized Losses	-68	-277
Held to maturity
Less Than 12 Months, Fair Value	28,786	235,016
Less than 12 Months, Unrealized Losses	-130	-4,330
12 Months or More, Fair Value	14,238	1,301
12 Months or More, Unrealized Losses	-252	-36
Total Fair Value	43,024	236,317
Total Unrealized Losses	-382	-4,366
Residential mortgage-backed securities
Available for Sale
Less Than 12 Months, Fair Value	235,818	232,807
Less Than 12 Months, Unrealized Losses	-1,336	-2,905
12 Months or More, Fair Value	29,373	44,182
12 Months or More, Unrealized Losses	-491	-832
Total Fair Value	265,191	276,989
Total Unrealized Losses	-1,827	-3,737
Commercial mortgage-backed securities
Available for Sale
Less Than 12 Months, Fair Value	89,509
Less Than 12 Months, Unrealized Losses	-220
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Total Fair Value	89,509
Total Unrealized Losses	-220
Corporate bonds
Available for Sale
Less Than 12 Months, Fair Value	62,693	122,344
Less Than 12 Months, Unrealized Losses	-1,159	-2,606
12 Months or More, Fair Value	9,675	705
12 Months or More, Unrealized Losses	-1,592	-4
Total Fair Value	72,368	123,049
Total Unrealized Losses	-2,751	-2,610
Equity securities
Available for Sale
Less Than 12 Months, Fair Value		10,457
Less Than 12 Months, Unrealized Losses		-192
12 Months or More, Fair Value		0
12 Months or More, Unrealized Losses		0
Total Fair Value		10,457
Total Unrealized Losses		($192)

Investment_Securities_Details_1

Investment Securities (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amortized cost and fair value of investment securities by contractual maturity
Pledged Financial Instruments, Not Separately Reported, Securities	$1,500,000,000	$1,200,000,000
Pledged Financial Instruments, Not Separately Reported, Securities Required to be Pledged	980,400,000	908,400,000
Realized net gains on the sale of investment securities available for sale
Realized gains	2,045,000	15,000	787,000
Realized losses	-4,478,000	-2,000	-8,000
Impairment charges	-92,000	-14,000	-224,000
Net (losses) gains	-2,525,000	-1,000	555,000
Amortized Cost, Available for sale
Due in one year or less	13,752,000
Due after one year through five years	305,172,000
Due after five years through ten years	39,903,000
Due after ten years	355,387,000
Amortized Cost	1,624,268,000	1,111,922,000
Fair Value, Available for sale
Due in one year or less	13,792,000
Due after one year through five years	306,103,000
Due after five years through ten years	40,823,000
Due after ten years	375,212,000
Fair Value	1,654,752,000	1,118,912,000
Amortized Cost, Held to maturity
Due in one year or less	29,060,000
Due in after one year through five years	247,683,000
Due after five years through ten years	102,901,000
Due after ten years	372,914,000
Investment securities held to maturity	993,380,000	1,182,533,000
Fair value, Held to maturity
Due in one year or less	29,114,000
Due in after one year through five years	249,058,000
Due after five years through ten years	106,556,000
Due after ten years	397,537,000
Investment Securities held to maturity	1,035,061,000	1,198,929,000
Total Available for Sale and Held to Maturity Investment Securities
Amortized Cost	2,617,648,000	2,294,455,000
Fair Value	2,689,813,000	2,317,841,000
Investment securities pledged as collateral for Federal Home Loan Bank advances	226,900,000	29,000,000
Equity securities
Amortized Cost, Available for sale
Amortized Cost	10,531,000	10,649,000
Fair Value, Available for sale
Fair Value	10,597,000	10,457,000
Residential and commercial mortgage-backed securities
Amortized Cost, Available for sale
Amortized Cost	899,523,000
Fair Value, Available for sale
Fair Value	908,225,000
Residential mortgage-backed securities
Amortized Cost, Available for sale
Amortized Cost	713,413,000	696,415,000
Fair Value, Available for sale
Fair Value	720,563,000	701,233,000
Amortized Cost, Held to maturity
Investment securities held to maturity	240,822,000	249,578,000
Fair value, Held to maturity
Investment Securities held to maturity	$252,796,000	$262,756,000

Loans_Details

Loans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
	investmentrating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased credit impaired and covered loans	$251,645,000	$235,720,000
Total loans, excluding purchased credit impaired and covered loans	8,831,572,000	5,476,831,000
Purchased credit impaired and covered loans	69,057,000
Total loans	9,083,217,000	5,712,551,000
Number of highest rating categories by rating services company	1
Number of highest rating categories to be achieved for classification as investment grade companies	4
Loans and leases receivable related parties	63,100,000	24,000,000
Loans and leases receivable related parties additions	7,900,000
Loans and leases receivable related parties collections	-14,900,000
Percentage of collateral pledge of first mortgage loans as per agreement	133.00%
Percentage of collateral pledge of home equity loans as per agreement	250.00%
Loans pledged as collateral for Federal Home Loan Bank advances	2,000,000,000	518,400,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	3,245,206,000	1,281,377,000
Purchased credit impaired and covered loans	1,139,000
Total loans	3,348,788,000	1,300,018,000
Commercial collateralized by assignment of lease payments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	1,692,258,000	1,494,188,000
Total loans	1,692,258,000	1,494,188,000
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	2,544,867,000	1,647,700,000
Purchased credit impaired and covered loans	37,017,000
Total loans	2,625,245,000	1,788,204,000
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	503,287,000	314,440,000
Total loans	517,425,000	316,275,000
Construction real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	247,068,000	141,253,000
Purchased credit impaired and covered loans	4,597,000
Total loans	278,136,000	189,566,000
Indirect vehicle
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	268,840,000	262,632,000
Total loans	268,840,000	262,632,000
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	251,909,000	268,289,000
Total loans	252,047,000	268,396,000
Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	78,137,000	66,952,000
Total loans	$100,478,000	$93,272,000

Loans_Details_2

Loans (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	$8,831,572	$5,476,831
Total loans	9,083,217	5,712,551
Period past due of recorded investment in loans (in days)	90 days
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,231,571	1,273,302
30-59 days, past due	8,222	5,952
60-89 days, past due	0	626
Loans past due, 90 days or more	5,413	1,497
Total, past due	13,635	8,075
Total loans, excluding covered loans	3,245,206	1,281,377
Total loans	3,348,788	1,300,018
Commercial collateralized by assignment of lease payments
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,679,991	1,489,391
30-59 days, past due	2,025	3,841
60-89 days, past due	6,095	656
Loans past due, 90 days or more	4,147	300
Total, past due	12,267	4,797
Total loans, excluding covered loans	1,692,258	1,494,188
Total loans	1,692,258	1,494,188
Healthcare
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	342,984	213,665
30-59 days, past due	0	0
60-89 days, past due	0	0
Loans past due, 90 days or more	0	3,064
Total, past due	0	3,064
Total loans, excluding covered loans	342,984	216,729
Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	333,907	372,975
30-59 days, past due	944	5,465
60-89 days, past due	0	0
Loans past due, 90 days or more	3,182	1,404
Total, past due	4,126	6,869
Total loans, excluding covered loans	338,033	379,844
Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	417,504	302,456
30-59 days, past due	1,377	3,078
60-89 days, past due	0	181
Loans past due, 90 days or more	1,517	2,226
Total, past due	2,894	5,485
Total loans, excluding covered loans	420,398	307,941
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	432,718	334,198
30-59 days, past due	2,481	328
60-89 days, past due	652	2,816
Loans past due, 90 days or more	2,325	7,258
Total, past due	5,458	10,402
Total loans, excluding covered loans	438,176	344,600
Office
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	244,166	155,936
30-59 days, past due	0	0
60-89 days, past due	0	0
Loans past due, 90 days or more	2,127	2,066
Total, past due	2,127	2,066
Total loans, excluding covered loans	246,293	158,002
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	754,031	233,464
30-59 days, past due	307	4,898
60-89 days, past due	2,421	259
Loans past due, 90 days or more	2,224	1,963
Total, past due	4,952	7,120
Total loans, excluding covered loans	758,983	240,584
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	485,492	302,362
30-59 days, past due	8,038	1,422
60-89 days, past due	2,319	1,030
Loans past due, 90 days or more	7,438	9,626
Total, past due	17,795	12,078
Total loans, excluding covered loans	503,287	314,440
Total loans	517,425	316,275
Construction real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	246,731	138,563
30-59 days, past due	0	391
60-89 days, past due	0	0
Loans past due, 90 days or more	337	2,299
Total, past due	337	2,690
Total loans, excluding covered loans	247,068	141,253
Total loans	278,136	189,566
Indirect vehicle
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	265,296	259,488
30-59 days, past due	2,516	2,210
60-89 days, past due	702	657
Loans past due, 90 days or more	326	277
Total, past due	3,544	3,144
Total loans, excluding covered loans	268,840	262,632
Total loans	268,840	262,632
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	242,756	257,219
30-59 days, past due	2,717	1,725
60-89 days, past due	1,039	2,165
Loans past due, 90 days or more	5,397	7,180
Total, past due	9,153	11,070
Total loans, excluding covered loans	251,909	268,289
Total loans	252,047	268,396
Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	78,106	66,866
30-59 days, past due	16	81
60-89 days, past due	12	1
Loans past due, 90 days or more	3	4
Total, past due	31	86
Total loans, excluding covered loans	78,137	66,952
Total loans	100,478	93,272
Gross Loans Excluding Purchase Credit Impaired And Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,755,253
30-59 days, past due	28,643
60-89 days, past due	13,240
Loans past due, 90 days or more	34,436
Total, past due	76,319
Total loans, excluding purchased credit impaired and covered loans	8,831,572
Purchased Credit Impaired And Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	158,215
30-59 days, past due	4,432
60-89 days, past due	585
Loans past due, 90 days or more	88,413
Total, past due	93,430
Total loans	251,645
Other Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding covered loans	1,102,173	912,313
Gross loans, excluding covered loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		5,399,885
30-59 days, past due		29,391
60-89 days, past due		8,391
Loans past due, 90 days or more		39,164
Total, past due		76,946
Total loans, excluding covered loans		5,476,831
Covered loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current		135,717
30-59 days, past due		902
60-89 days, past due		3,346
Loans past due, 90 days or more		95,755
Total, past due		100,003
Total loans		235,720
Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,913,468	5,535,602
30-59 days, past due	33,075	30,293
60-89 days, past due	13,825	11,737
Loans past due, 90 days or more	122,849	134,919
Total, past due	169,749	176,949
Total loans	9,083,217	5,712,551
Non-performing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	46,149	56,339
30-59 days, past due	5,764	14,325
60-89 days, past due	1,099	3,283
Loans past due, 90 days or more	34,075	32,614
Total, past due	40,938	50,222
Total loans, excluding covered loans	34,029	25,446
Total loans	87,087	106,561
Non-performing | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding covered loans	17,311	13,009
Non-performing | Indirect vehicle
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding covered loans	1,543	1,459
Non-performing | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding covered loans	15,170	10,969
Non-performing | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding covered loans	$5	$9

Loans_Details_3

Loans (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Reduction in interest income associated with loans on nonaccrual status	$4,300,000	$4,700,000	$5,600,000
Commercial
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	14,088,000	17,781,000
Loans past due 90 days or more and still accruing	0	0
Commercial collateralized by assignment of lease payments
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	2,404,000	4,276,000
Loans past due 90 days or more and still accruing	3,566,000	291,000
Healthcare
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	0	3,064,000
Loans past due 90 days or more and still accruing	0	0
Industrial
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	6,371,000	15,265,000
Loans past due 90 days or more and still accruing	0	155,000
Multifamily
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	5,333,000	5,145,000
Loans past due 90 days or more and still accruing	0	0
Office
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	3,644,000	11,703,000
Loans past due 90 days or more and still accruing	464,000	0
Retail
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	2,986,000	2,969,000
Loans past due 90 days or more and still accruing	0	0
Other
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	13,541,000	19,991,000
Loans past due 90 days or more and still accruing	324,000	0
Residential real estate
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	17,311,000	13,009,000
Loans past due 90 days or more and still accruing	0	0
Construction real estate
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	337,000	475,000
Loans past due 90 days or more and still accruing	0	0
Indirect vehicle
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	1,542,000	1,459,000
Loans past due 90 days or more and still accruing	0	0
Loans
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	82,733,000	106,115,000
Loans past due 90 days or more and still accruing	4,354,000	446,000
Non-performing | Home equity
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	15,171,000	10,969,000
Loans past due 90 days or more and still accruing	0	0
Non-performing | Other consumer
Financing Receivable Recorded Investment Non Accrual and Past Due [Abstract]
Nonaccrual	5,000	9,000
Loans past due 90 days or more and still accruing	$0	$0

Loans_Details_4

Loans (Details 4) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-performing substandard and doubtful loans	$49,100,000	$80,700,000
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	3,245,206,000	1,281,377,000
Commercial collateralized by assignment of lease payments
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	1,692,258,000	1,494,188,000
Healthcare
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	342,984,000	216,729,000
Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	338,033,000	379,844,000
Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	420,398,000	307,941,000
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	438,176,000	344,600,000
Office
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	246,293,000	158,002,000
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	758,983,000	240,584,000
Construction real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	247,068,000	141,253,000
Pass
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	7,390,916,000	4,335,981,000
Pass | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	3,036,069,000	1,193,114,000
Pass | Commercial collateralized by assignment of lease payments
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	1,680,736,000	1,486,899,000
Pass | Healthcare
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	338,622,000	189,705,000
Pass | Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	314,225,000	345,236,000
Pass | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	412,824,000	296,179,000
Pass | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	423,842,000	316,420,000
Pass | Office
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	229,947,000	151,393,000
Pass | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	708,447,000	217,188,000
Pass | Construction real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	246,204,000	139,847,000
Special Mention
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	233,740,000	68,277,000
Special Mention | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	178,984,000	26,637,000
Special Mention | Commercial collateralized by assignment of lease payments
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	6,853,000	553,000
Special Mention | Healthcare
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	4,362,000	21,186,000
Special Mention | Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	8,817,000	5,328,000
Special Mention | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	920,000	342,000
Special Mention | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	2,740,000	10,660,000
Special Mention | Office
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	8,524,000	2,682,000
Special Mention | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	22,013,000	349,000
Special Mention | Construction real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	527,000	540,000
Substandard
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	104,743,000	156,570,000
Substandard | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	30,153,000	61,000,000
Substandard | Commercial collateralized by assignment of lease payments
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	4,669,000	6,736,000
Substandard | Healthcare
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	2,774,000
Substandard | Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	14,991,000	29,280,000
Substandard | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	6,654,000	11,420,000
Substandard | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	11,594,000	17,520,000
Substandard | Office
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	7,822,000	3,927,000
Substandard | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	28,523,000	23,047,000
Substandard | Construction real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	337,000	866,000
Doubtful
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	3,690,000
Doubtful | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	626,000
Doubtful | Commercial collateralized by assignment of lease payments
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	0
Doubtful | Healthcare
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	3,064,000
Doubtful | Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	0
Doubtful | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	0
Doubtful | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	0
Doubtful | Office
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	0
Doubtful | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	0
Doubtful | Construction real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	0	0
Risk Rated Category
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	7,729,399,000	4,564,518,000
Risk Rated Category | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	3,245,206,000	1,281,377,000
Risk Rated Category | Commercial collateralized by assignment of lease payments
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	1,692,258,000	1,494,188,000
Risk Rated Category | Healthcare
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	342,984,000	216,729,000
Risk Rated Category | Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	338,033,000	379,844,000
Risk Rated Category | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	420,398,000	307,941,000
Risk Rated Category | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	438,176,000	344,600,000
Risk Rated Category | Office
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	246,293,000	158,002,000
Risk Rated Category | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	758,983,000	240,584,000
Risk Rated Category | Construction real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans, excluding purchased credit impaired and covered loans	$247,068,000	$141,253,000

Loans_Details_5

Loans (Details 5) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	$503,287	$314,440
Indirect vehicle
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	268,840	262,632
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	251,909	268,289
Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	78,137	66,952
Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	1,102,173	912,313
Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	1,068,144	886,867
Performing | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	485,976	301,431
Performing | Indirect vehicle
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	267,297	261,173
Performing | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	236,739	257,320
Performing | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	78,132	66,943
Non-performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	34,029	25,446
Non-performing | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	17,311	13,009
Non-performing | Indirect vehicle
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	1,543	1,459
Non-performing | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	15,170	10,969
Non-performing | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, excluding purchased credit impaired and covered loans	$5	$9

Loans_Details_6

Loans (Details 6) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	$113,336,000	$135,041,000
Recorded Investment	101,532,000	128,521,000
Partial Charge-Offs	11,804,000	6,520,000
Allowance for Loan Losses Allocated	10,482,000	17,368,000
Average Recorded Investment	126,665,000	136,454,000	119,300,000
Interest Income Recognized	407,000	1,870,000
Interest income recognized on cash basis	400,000	1,900,000	1,600,000
Restructured loans	9,269,000
Performing
Loans individually evaluated for impairment by class of loans
Restructured loans	15,600,000	29,400,000
Non-performing
Loans individually evaluated for impairment by class of loans
Restructured loans	25,800,000	25,000,000
Commercial
Loans individually evaluated for impairment by class of loans
Restructured loans	263,000
Multifamily
Loans individually evaluated for impairment by class of loans
Restructured loans	158,000
Residential real estate
Loans individually evaluated for impairment by class of loans
Restructured loans	2,438,000
Indirect vehicle
Loans individually evaluated for impairment by class of loans
Restructured loans	346,000
Home equity
Loans individually evaluated for impairment by class of loans
Restructured loans	6,064,000
Impaired financing receivable with no allowance | Commercial
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	9,752,000	8,903,000
Recorded Investment	8,992,000	8,903,000
Partial Charge-Offs	760,000	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	10,324,000	8,259,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Commercial collateralized by assignment of lease payments
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	2,316,000	3,401,000
Recorded Investment	2,316,000	3,401,000
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	2,569,000	1,030,000
Interest Income Recognized	121,000	6,000
Impaired financing receivable with no allowance | Healthcare
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	2,698,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Industrial
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	9,115,000	7,560,000
Recorded Investment	5,858,000	7,560,000
Partial Charge-Offs	3,257,000	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	7,870,000	8,900,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Multifamily
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	1,733,000	1,166,000
Recorded Investment	1,733,000	1,166,000
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	1,928,000	758,000
Interest Income Recognized	52,000	11,000
Impaired financing receivable with no allowance | Retail
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	2,025,000	4,466,000
Recorded Investment	813,000	4,466,000
Partial Charge-Offs	1,212,000	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	3,465,000	3,628,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Office
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	0	559,000
Recorded Investment	0	527,000
Partial Charge-Offs	0	32,000
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	1,127,000	922,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Other
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	1,479,000	2,963,000
Recorded Investment	1,465,000	2,963,000
Partial Charge-Offs	14,000	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	5,249,000	4,380,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Residential real estate
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	1,941,000	4,234,000
Recorded Investment	1,941,000	4,234,000
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	2,740,000	3,260,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Construction real estate
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	34,000	0
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Indirect vehicle
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Home equity
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	577,000	577,000
Recorded Investment	577,000	577,000
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	762,000	797,000
Interest Income Recognized	0	0
Impaired financing receivable with no allowance | Other consumer
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Impaired financing receivable with allowance | Commercial
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	7,987,000	8,923,000
Recorded Investment	7,987,000	8,919,000
Partial Charge-Offs	0	4,000
Allowance for Loan Losses Allocated	2,395,000	4,284,000
Average Recorded Investment	14,227,000	13,476,000
Interest Income Recognized	0	4,000
Impaired financing receivable with allowance | Commercial collateralized by assignment of lease payments
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	715,000	1,060,000
Recorded Investment	715,000	1,060,000
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	105,000	144,000
Average Recorded Investment	1,515,000	1,279,000
Interest Income Recognized	91,000	192,000
Impaired financing receivable with allowance | Healthcare
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	0	3,186,000
Recorded Investment	0	3,064,000
Partial Charge-Offs	0	122,000
Allowance for Loan Losses Allocated	0	382,000
Average Recorded Investment	0	8,189,000
Interest Income Recognized	0	0
Impaired financing receivable with allowance | Industrial
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	517,000	7,707,000
Recorded Investment	513,000	7,705,000
Partial Charge-Offs	4,000	2,000
Allowance for Loan Losses Allocated	130,000	3,038,000
Average Recorded Investment	4,982,000	3,699,000
Interest Income Recognized	0	0
Impaired financing receivable with allowance | Multifamily
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	5,680,000	5,374,000
Recorded Investment	4,709,000	5,374,000
Partial Charge-Offs	971,000	0
Allowance for Loan Losses Allocated	996,000	1,661,000
Average Recorded Investment	6,354,000	6,443,000
Interest Income Recognized	131,000	340,000
Impaired financing receivable with allowance | Retail
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	9,264,000	14,169,000
Recorded Investment	7,897,000	12,428,000
Partial Charge-Offs	1,367,000	1,741,000
Allowance for Loan Losses Allocated	720,000	1,511,000
Average Recorded Investment	8,547,000	12,885,000
Interest Income Recognized	0	280,000
Impaired financing receivable with allowance | Office
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	4,528,000	2,442,000
Recorded Investment	2,986,000	2,442,000
Partial Charge-Offs	1,542,000	0
Allowance for Loan Losses Allocated	545,000	791,000
Average Recorded Investment	2,833,000	4,045,000
Interest Income Recognized	0	0
Impaired financing receivable with allowance | Other
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	12,612,000	20,367,000
Recorded Investment	12,527,000	17,029,000
Partial Charge-Offs	85,000	3,338,000
Allowance for Loan Losses Allocated	136,000	796,000
Average Recorded Investment	11,022,000	12,868,000
Interest Income Recognized	12,000	20,000
Impaired financing receivable with allowance | Residential real estate
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	14,234,000	13,496,000
Recorded Investment	14,234,000	12,710,000
Partial Charge-Offs	0	786,000
Allowance for Loan Losses Allocated	3,126,000	3,119,000
Average Recorded Investment	14,632,000	12,966,000
Interest Income Recognized	0	245,000
Impaired financing receivable with allowance | Construction real estate
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	2,707,000	475,000
Recorded Investment	337,000	475,000
Partial Charge-Offs	2,370,000	0
Allowance for Loan Losses Allocated	162,000	227,000
Average Recorded Investment	455,000	1,603,000
Interest Income Recognized	0	0
Impaired financing receivable with allowance | Indirect vehicle
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	227,000	173,000
Recorded Investment	227,000	123,000
Partial Charge-Offs	0	50,000
Allowance for Loan Losses Allocated	14,000	57,000
Average Recorded Investment	358,000	86,000
Interest Income Recognized	0	0
Impaired financing receivable with allowance | Home equity
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	25,927,000	23,840,000
Recorded Investment	25,705,000	23,395,000
Partial Charge-Offs	222,000	445,000
Allowance for Loan Losses Allocated	2,153,000	1,358,000
Average Recorded Investment	25,672,000	24,283,000
Interest Income Recognized	0	772,000
Impaired financing receivable with allowance | Other consumer
Loans individually evaluated for impairment by class of loans
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Partial Charge-Offs	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	0
Interest Income Recognized	$0	$0

Loans_Details_7

Loans (Details 7) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
	loan	loan
Restructured loans
Number of separate notes restructured into A/B by the company	2
Minimum period of sustained repayment required to return the note to accrual status (in months)	6 months
Restructured loans representing A/B structures	$1,000,000	$1,100,000
Number of A/B structures represented by restructured loans	1
Redefaulted loans	188,000
Period past due of recorded redefaulted loans (in days)	90 days
Troubled Debt Restructuring Activity [Roll Forward]
Ending balance	9,269,000
Performing
Restructured loans
Number of loans	14	21
Pre-Modification Recorded Investment	2,865,000	3,715,000
Post-Modification Recorded Investment	2,865,000	3,715,000
Charge-offs and Specific Reserves	0	0
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	29,430,000
Additions	2,865,000
Charge-offs	-451,000
Principal payments, net	-2,650,000
Removals	-8,574,000
Transfer to other real estate owned	0
Transfer from non-performing/performing	6,407,000
Transfer to non-performing/performing	-11,424,000
Ending balance	15,603,000	29,430,000
Non-performing
Restructured loans
Number of loans	88	75
Pre-Modification Recorded Investment	6,404,000	17,359,000
Post-Modification Recorded Investment	6,404,000	17,196,000
Charge-offs and Specific Reserves	794,000	3,184,000
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	24,952,000
Additions	6,404,000
Charge-offs	-2,840,000
Principal payments, net	-3,965,000
Removals	-3,576,000
Transfer to other real estate owned	-221,000
Transfer from non-performing/performing	11,424,000
Transfer to non-performing/performing	-6,407,000
Ending balance	25,771,000	24,952,000
Commercial
Troubled Debt Restructuring Activity [Roll Forward]
Ending balance	263,000
Commercial | Non-performing
Restructured loans
Number of loans	1	2
Pre-Modification Recorded Investment	263,000	1,251,000
Post-Modification Recorded Investment	263,000	1,251,000
Charge-offs and Specific Reserves	85,000	673,000
Commercial collateralized by assignment of lease payments | Non-performing
Restructured loans
Number of loans		1
Pre-Modification Recorded Investment		3,401,000
Post-Modification Recorded Investment		3,401,000
Charge-offs and Specific Reserves		0
Healthcare | Non-performing
Restructured loans
Number of loans		1
Pre-Modification Recorded Investment		3,164,000
Post-Modification Recorded Investment		3,164,000
Charge-offs and Specific Reserves		496,000
Industrial | Non-performing
Restructured loans
Number of loans		4
Pre-Modification Recorded Investment		2,570,000
Post-Modification Recorded Investment		2,570,000
Charge-offs and Specific Reserves		1,425,000
Multifamily
Troubled Debt Restructuring Activity [Roll Forward]
Ending balance	158,000
Multifamily | Performing
Restructured loans
Number of loans		1
Pre-Modification Recorded Investment		601,000
Post-Modification Recorded Investment		601,000
Charge-offs and Specific Reserves		0
Multifamily | Non-performing
Restructured loans
Number of loans	1	2
Pre-Modification Recorded Investment	158,000	623,000
Post-Modification Recorded Investment	158,000	623,000
Charge-offs and Specific Reserves	40,000	169,000
Retail | Non-performing
Restructured loans
Number of loans		3
Pre-Modification Recorded Investment		862,000
Post-Modification Recorded Investment		862,000
Charge-offs and Specific Reserves		235,000
Other | Non-performing
Restructured loans
Number of loans		1
Pre-Modification Recorded Investment		84,000
Post-Modification Recorded Investment		84,000
Charge-offs and Specific Reserves		23,000
Residential real estate
Troubled Debt Restructuring Activity [Roll Forward]
Ending balance	2,438,000
Residential real estate | Performing
Restructured loans
Number of loans	3	6
Pre-Modification Recorded Investment	588,000	910,000
Post-Modification Recorded Investment	588,000	910,000
Charge-offs and Specific Reserves	0	0
Residential real estate | Non-performing
Restructured loans
Number of loans	6	9
Pre-Modification Recorded Investment	1,850,000	1,803,000
Post-Modification Recorded Investment	1,850,000	1,682,000
Charge-offs and Specific Reserves	246,000	121,000
Indirect vehicle
Troubled Debt Restructuring Activity [Roll Forward]
Ending balance	346,000
Indirect vehicle | Performing
Restructured loans
Number of loans	2
Pre-Modification Recorded Investment	26,000
Post-Modification Recorded Investment	26,000
Charge-offs and Specific Reserves	0
Indirect vehicle | Non-performing
Restructured loans
Number of loans	53	26
Pre-Modification Recorded Investment	320,000	171,000
Post-Modification Recorded Investment	320,000	129,000
Charge-offs and Specific Reserves	88,000	42,000
Home equity
Troubled Debt Restructuring Activity [Roll Forward]
Ending balance	6,064,000
Home equity | Performing
Restructured loans
Number of loans	9	14
Pre-Modification Recorded Investment	2,251,000	2,204,000
Post-Modification Recorded Investment	2,251,000	2,204,000
Charge-offs and Specific Reserves	0	0
Home equity | Non-performing
Restructured loans
Number of loans	27	26
Pre-Modification Recorded Investment	3,813,000	3,430,000
Post-Modification Recorded Investment	3,813,000	3,430,000
Charge-offs and Specific Reserves	$335,000	$0

Loans_Details_8

Loans (Details 8) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Financing Receivable, Allowance for Credit Losses [Line Items]
Extended Maturity, Amortization and Reduction of Interest Rate	$2,795
Extended Maturity, Delay in Payments and Reduction of Interest Rate	878
Extended Maturity and Delay in Payments or Reduction of Interest Rate	2,900
Delay in Payments or Reduction of Interest Rate	2,696
Total	9,269
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Extended Maturity, Amortization and Reduction of Interest Rate	0
Extended Maturity, Delay in Payments and Reduction of Interest Rate	0
Extended Maturity and Delay in Payments or Reduction of Interest Rate	263
Delay in Payments or Reduction of Interest Rate	0
Total	263
Multifamily
Financing Receivable, Allowance for Credit Losses [Line Items]
Extended Maturity, Amortization and Reduction of Interest Rate	0
Extended Maturity, Delay in Payments and Reduction of Interest Rate	0
Extended Maturity and Delay in Payments or Reduction of Interest Rate	158
Delay in Payments or Reduction of Interest Rate	0
Total	158
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Extended Maturity, Amortization and Reduction of Interest Rate	411
Extended Maturity, Delay in Payments and Reduction of Interest Rate	0
Extended Maturity and Delay in Payments or Reduction of Interest Rate	1,268
Delay in Payments or Reduction of Interest Rate	759
Total	2,438
Indirect vehicle
Financing Receivable, Allowance for Credit Losses [Line Items]
Extended Maturity, Amortization and Reduction of Interest Rate	0
Extended Maturity, Delay in Payments and Reduction of Interest Rate	0
Extended Maturity and Delay in Payments or Reduction of Interest Rate	0
Delay in Payments or Reduction of Interest Rate	346
Total	346
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Extended Maturity, Amortization and Reduction of Interest Rate	2,384
Extended Maturity, Delay in Payments and Reduction of Interest Rate	878
Extended Maturity and Delay in Payments or Reduction of Interest Rate	1,211
Delay in Payments or Reduction of Interest Rate	1,591
Total	$6,064

Loans_Details_9

Loans (Details 9) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses, beginning balance	$113,462	$128,279	$135,975
Allowance for unfunded credit commitments acquired through business combination	1,261	0	0
Utilization of allowance for unfunded credit commitments	-637	0	0
Provision for credit losses	12,052	-5,804	-8,900
Total charge-offs	24,745	23,675	30,616
Total recoveries	12,664	14,662	31,820
Net charge-offs	12,081	9,013	-1,204
Allowance for credit losses, ending balance	114,057	113,462	128,279
Allowance for unfunded credit commitments	-4,031	-1,716	-4,075
Ending Balance	110,026	111,746	124,204
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	1,339	3,706	2,408
Recoveries	3,757	3,156	3,475
Ending Balance	29,571	23,461	24,943
Commercial collateralized by assignment of lease payments
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	586	0	1,721
Recoveries	939	1,131	6,720
Ending Balance	9,962	9,159	7,755
Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	11,438	7,517	11,377
Recoveries	4,020	6,025	16,987
Ending Balance	41,826	51,628	61,056
Residential real estate
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	1,718	2,796	2,944
Recoveries	1,190	479	501
Ending Balance	6,646	8,872	6,941
Construction real estate
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	79	980	4,007
Recoveries	252	1,616	2,019
Ending Balance	8,918	6,856	11,222
Indirect vehicle
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	3,735	2,911	2,259
Recoveries	1,736	1,411	1,096
Ending Balance	1,687	1,662	1,324
Home equity
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	3,383	3,692	4,551
Recoveries	482	594	671
Ending Balance	9,456	8,478	9,401
Other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs	2,467	2,073	1,349
Recoveries	288	250	351
Ending Balance	$1,960	$1,630	$1,562

Loans_Details_10

Loans (Details 10) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Allowance for credit losses:
Beginning balance	$111,746,000		$124,204,000
Transfer to (from) allowance for unfunded credit commitments			-500,000
Ending Balance	110,026,000		111,746,000		124,204,000
Ending allowance balance attributable to loans:
Acquired and accounted for under ASC 310-30	1,283,000	[1]	2,232,000	[1]
Total ending allowance balance	110,026,000		111,746,000		124,204,000
Loans:
Individually evaluated for impairment	101,532,000		128,521,000
Collectively evaluated for impairment	8,730,040,000		5,327,665,000
Acquired and accounted for under ASC 310-30	251,645,000	[1]	256,365,000	[1]
Total loans	9,083,217,000		5,712,551,000
Unfunded Commitments:
Beginning balance	1,716,000		4,075,000
Allowance for unfunded credit commitments acquired through business combination	1,261,000
Utilization of allowance for unfunded credit commitments	-637,000
Transfer to (from) allowance for unfunded credit commitments			-500,000
Provision	1,691,000		-1,859,000
Ending balance	4,031,000		1,716,000		4,075,000
Unfunded commitments ending allowance balance:
Individually evaluated for impairment for unfunded commitments	1,348,000		689,000
Unfunded commitments collectively evaluated for impairment	2,683,000		1,027,000
Total ending allowance balance	4,031,000		1,716,000		4,075,000
Allowance for credit losses
Allowance for credit losses, beginning balance	113,462,000		128,279,000		135,975,000
Allowance for credit losses, Allowance for unfunded credit commitments acquired through business combination	1,261,000		0		0
Allowance for credit losses, Utilization of allowance for unfunded credit commitments	-637,000		0		0
Allowance for credit losses, Charge-offs	24,745,000		23,675,000		30,616,000
Allowance for credit losses, Recoveries	12,664,000		14,662,000		31,820,000
Allowance for credit losses, Provision	12,052,000		-5,804,000
Allowance for credit losses, ending balance	114,057,000		113,462,000		128,279,000
Allowance for credit losses ending allowance balance:
Allowance for credit losses, individually evaluated for impairment	11,830,000		18,057,000
Allowance for credit losses, collectively evaluated for impairment	100,944,000		93,173,000
Acquired and accounted for under ASC 310-30	1,283,000	[1]	2,232,000	[1]
Total ending allowance balance	114,057,000		113,462,000		128,279,000
Net charge-offs (recoveries)	12,081,000		9,013,000		-1,204,000
Purchase Credit Impaired Loan
Allowance for credit losses:
Provision	-1,300,000		2,500,000
Loans:
Total loans	71,700,000		195,500,000
Allowance for credit losses ending allowance balance:
Provision and charge-offs related to the number of pools	16		15
Net charge-offs (recoveries)	-323,000		-218,000
Commercial
Allowance for credit losses:
Beginning balance	23,461,000		24,943,000
Charge-offs	1,339,000		3,706,000		2,408,000
Recoveries	3,757,000		3,156,000		3,475,000
Provision	3,692,000		-932,000
Ending Balance	29,571,000		23,461,000		24,943,000
Ending allowance balance attributable to loans:
Individually evaluated for impairment	2,395,000		4,284,000
Collectively evaluated for impairment	26,684,000		18,693,000
Acquired and accounted for under ASC 310-30	492,000	[1]	484,000	[1]
Total ending allowance balance	29,571,000		23,461,000		24,943,000
Loans:
Individually evaluated for impairment	16,979,000		17,822,000
Collectively evaluated for impairment	3,228,227,000		1,246,523,000
Acquired and accounted for under ASC 310-30	103,582,000	[1]	35,673,000	[1]
Total loans	3,348,788,000		1,300,018,000
Allowance for credit losses ending allowance balance:
Acquired and accounted for under ASC 310-30	492,000	[1]	484,000	[1]
Commercial collateralized by assignment of lease payments
Allowance for credit losses:
Beginning balance	9,159,000		7,755,000
Charge-offs	586,000		0		1,721,000
Recoveries	939,000		1,131,000		6,720,000
Provision	450,000		273,000
Ending Balance	9,962,000		9,159,000		7,755,000
Ending allowance balance attributable to loans:
Individually evaluated for impairment	105,000		144,000
Collectively evaluated for impairment	9,857,000		9,015,000
Total ending allowance balance	9,962,000		9,159,000		7,755,000
Loans:
Individually evaluated for impairment	3,031,000		4,461,000
Collectively evaluated for impairment	1,689,227,000		1,489,727,000
Total loans	1,692,258,000		1,494,188,000
Commercial real estate
Allowance for credit losses:
Beginning balance	51,628,000		61,056,000
Charge-offs	11,438,000		7,517,000		11,377,000
Recoveries	4,020,000		6,025,000		16,987,000
Provision	-2,384,000		-7,936,000
Ending Balance	41,826,000		51,628,000		61,056,000
Ending allowance balance attributable to loans:
Individually evaluated for impairment	2,527,000		8,179,000
Collectively evaluated for impairment	38,517,000		41,763,000
Acquired and accounted for under ASC 310-30	782,000	[1]	1,686,000	[1]
Total ending allowance balance	41,826,000		51,628,000		61,056,000
Loans:
Individually evaluated for impairment	38,501,000		64,724,000
Collectively evaluated for impairment	2,506,366,000		1,582,976,000
Acquired and accounted for under ASC 310-30	80,378,000	[1]	140,504,000	[1]
Total loans	2,625,245,000		1,788,204,000
Allowance for credit losses ending allowance balance:
Acquired and accounted for under ASC 310-30	782,000	[1]	1,686,000	[1]
Allowance for loan losses and unfunded commitments acquired with deteriorated credit quality	1,300,000		2,200,000
Residential real estate
Allowance for credit losses:
Beginning balance	8,872,000		6,941,000
Charge-offs	1,718,000		2,796,000		2,944,000
Recoveries	1,190,000		479,000		501,000
Provision	-1,698,000		4,248,000
Ending Balance	6,646,000		8,872,000		6,941,000
Ending allowance balance attributable to loans:
Individually evaluated for impairment	3,126,000		3,119,000
Collectively evaluated for impairment	3,520,000		5,753,000
Total ending allowance balance	6,646,000		8,872,000		6,941,000
Loans:
Individually evaluated for impairment	16,175,000		16,944,000
Collectively evaluated for impairment	487,112,000		293,883,000
Acquired and accounted for under ASC 310-30	14,138,000	[1]	5,448,000	[1]
Total loans	517,425,000		316,275,000
Construction real estate
Allowance for credit losses:
Beginning balance	6,856,000		11,222,000
Transfer to (from) allowance for unfunded credit commitments			500,000
Charge-offs	79,000		980,000		4,007,000
Recoveries	252,000		1,616,000		2,019,000
Provision	1,889,000		-5,502,000
Ending Balance	8,918,000		6,856,000		11,222,000
Ending allowance balance attributable to loans:
Individually evaluated for impairment	162,000		227,000
Collectively evaluated for impairment	8,747,000		6,567,000
Acquired and accounted for under ASC 310-30	9,000	[1]	62,000	[1]
Total ending allowance balance	8,918,000		6,856,000		11,222,000
Loans:
Individually evaluated for impairment	337,000		475,000
Collectively evaluated for impairment	246,731,000		140,778,000
Acquired and accounted for under ASC 310-30	31,068,000	[1]	48,313,000	[1]
Total loans	278,136,000		189,566,000
Unfunded Commitments:
Transfer to (from) allowance for unfunded credit commitments			500,000
Allowance for credit losses ending allowance balance:
Acquired and accounted for under ASC 310-30	9,000	[1]	62,000	[1]
Indirect vehicle
Allowance for credit losses:
Beginning balance	1,662,000		1,324,000
Charge-offs	3,735,000		2,911,000		2,259,000
Recoveries	1,736,000		1,411,000		1,096,000
Provision	2,024,000		1,838,000
Ending Balance	1,687,000		1,662,000		1,324,000
Ending allowance balance attributable to loans:
Individually evaluated for impairment	14,000		57,000
Collectively evaluated for impairment	1,673,000		1,605,000
Total ending allowance balance	1,687,000		1,662,000		1,324,000
Loans:
Individually evaluated for impairment	227,000		123,000
Collectively evaluated for impairment	268,613,000		262,509,000
Total loans	268,840,000		262,632,000
Home equity
Allowance for credit losses:
Beginning balance	8,478,000		9,401,000
Charge-offs	3,383,000		3,692,000		4,551,000
Recoveries	482,000		594,000		671,000
Provision	3,879,000		2,175,000
Ending Balance	9,456,000		8,478,000		9,401,000
Ending allowance balance attributable to loans:
Individually evaluated for impairment	2,153,000		1,358,000
Collectively evaluated for impairment	7,303,000		7,120,000
Total ending allowance balance	9,456,000		8,478,000		9,401,000
Loans:
Individually evaluated for impairment	26,282,000		23,972,000
Collectively evaluated for impairment	225,627,000		244,317,000
Acquired and accounted for under ASC 310-30	138,000	[1]	107,000	[1]
Total loans	252,047,000		268,396,000
Other consumer
Allowance for credit losses:
Beginning balance	1,630,000		1,562,000
Charge-offs	2,467,000		2,073,000		1,349,000
Recoveries	288,000		250,000		351,000
Provision	2,509,000		1,891,000
Ending Balance	1,960,000		1,630,000		1,562,000
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	1,960,000		1,630,000
Total ending allowance balance	1,960,000		1,630,000		1,562,000
Loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	78,137,000		66,952,000
Acquired and accounted for under ASC 310-30	22,341,000	[1]	26,320,000	[1]
Total loans	$100,478,000		$93,272,000
[1]	Loans acquired in the Taylor Capital merger and FDIC-assisted transactions and accounted for under ASC Subtopic 310-30 “Receivables — Loans and Debt Securities Acquired with Deteriorated Credit Quality.”

Loans_Details_11

Loans (Details 11) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Changes in the accretable yield for purchased credit-impaired loans
Balance at beginning of period	$2,337	$5,685
Purchases	5,626	0
Accretion	-2,098	-4,456
Other	1,569	1,108
Balance at end of period	$7,434	$2,337

Loans_Details_12

Loans (Details 12) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	$69,057,000
Estimated receivable amount from the FDIC under the loss-share agreement	2,663,000	[1]
Non covered loans	3,342,837,000
Outstanding balances on purchased loans from the FDIC	95,100,000		273,500,000
Carrying amount on loans purchased from the FDIC	91,400,000		261,400,000
Purchased Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	26,414,000
Estimated receivable amount from the FDIC under the loss-share agreement	-1,850,000	[1]
Non covered loans	182,588,000
Purchased Non-Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	42,643,000
Estimated receivable amount from the FDIC under the loss-share agreement	4,513,000	[1]
Non covered loans	3,160,249,000
Commercial related
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	2,805,000	[2]
Non covered loans	17,658,000	[3]
Commercial related | Purchased Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	706,000	[2]
Non covered loans	4,288,000	[3]
Reimbursable Amount Covered Other Real Estate Owned	303,000
Commercial related | Purchased Non-Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	2,099,000	[2]
Non covered loans	13,370,000	[3]
Commercial
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	1,139,000
Non covered loans	1,777,258,000
Commercial | Purchased Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	830,000
Non covered loans	95,350,000
Commercial | Purchased Non-Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	309,000
Non covered loans	1,681,908,000
Commercial collateralized by assignment of lease payments
Purchased credit-impaired loans and non-credit-impaired loans
Non covered loans	160,299,000
Commercial collateralized by assignment of lease payments | Purchased Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Non covered loans	0
Commercial collateralized by assignment of lease payments | Purchased Non-Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Non covered loans	160,299,000
Commercial real estate
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	37,017,000
Non covered loans	969,545,000
Commercial real estate | Purchased Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	20,489,000
Non covered loans	43,361,000
Commercial real estate | Purchased Non-Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	16,528,000
Non covered loans	926,184,000
Construction real estate
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	4,597,000
Non covered loans	173,038,000
Construction real estate | Purchased Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	2,512,000
Non covered loans	26,471,000
Construction real estate | Purchased Non-Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	2,085,000
Non covered loans	146,567,000
Other
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	23,499,000
Non covered loans	245,039,000
Other | Purchased Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	1,877,000
Non covered loans	13,118,000
Other | Purchased Non-Credit Impaired Loans Receivable
Purchased credit-impaired loans and non-credit-impaired loans
Purchased credit impaired and covered loans	21,622,000
Non covered loans	231,921,000
Commercial Loans, Commercial Real Estate Receivable And Construction Loans [Member]
Purchased credit-impaired loans and non-credit-impaired loans
Loans Not Covered Under the Loss Share Agreement	$2,800,000
[1]	Estimated reimbursable amounts from the FDIC under the loss-share agreement exclude $303 thousand in reimbursable amounts related to covered other real estate owned.
[2]	Covered commercial related loans include commercial, commercial real estate and construction real estate loans acquired in connection with the Benchmark FDIC-assisted transactions.
[3]	Non-covered commercial related loans include commercial, commercial real estate and construction real estate for InBank and Heritage.

Lease_Investments_Details

Lease Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Direct finance leases:
Minimum lease payments	$340,602,000		$155,945,000
Estimated unguaranteed residual values	70,469,000		31,272,000
Less: unearned income	-31,229,000		-14,473,000
Direct finance leases	379,842,000	[1]	172,744,000	[1]
Leveraged leases:
Minimum lease payments	10,689,000		24,320,000
Estimated unguaranteed residual values	1,586,000		2,508,000
Less: unearned income	-540,000		-1,644,000
Less: related non-recourse debt	-10,330,000		-23,243,000
Leveraged leases	1,405,000	[1]	1,941,000	[1]
Operating leases:
Equipment, at cost	257,495,000		218,473,000
Less accumulated depreciation	-94,662,000		-87,384,000
Lease investments, net	162,833,000		131,089,000
Minimum percentage of residual component in total equipment investment	10.00%
Loans at other banks for lease equipment purchases	$38,500,000		$17,500,000
[1]	Direct finance and leveraged leases are included as commercial loans collateralized by assignment of lease payments for financial statement purposes.

Lease_Investments_Details_2

Lease Investments (Details 2) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Minimum lease payments receivable for direct finance leases
2015	$122,353
2016	97,324
2017	66,223
2018	37,231
2019	13,457
Thereafter	4,014
Total	340,602
Minimum lease payments receivable for leveraged leases
2015	7,386
2016	2,482
2017	642
2018	179
2019	0
Thereafter	0
Total	10,689
Minimum lease payments receivable for operating leases
2015	40,624
2016	29,802
2017	20,461
2018	9,475
2019	5,143
Thereafter	3,205
Total	108,710
Minimum lease payments receivable for, total
2015	170,363
2016	129,608
2017	87,326
2018	46,885
2019	18,600
Thereafter	7,219
Total	$460,001

Lease_Investments_Details_3

Lease Investments (Details 3) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Residual values for leases by category in the year the initial lease term ends
2015	$12,501
2016	16,129
2017	29,885
2018	23,828
2019	18,408
Thereafter	28,552
Total	129,303
Direct Finance Leases
Residual values for leases by category in the year the initial lease term ends
2015	8,827
2016	7,597
2017	19,448
2018	14,544
2019	10,551
Thereafter	9,502
Total	70,469
Leveraged Leases
Residual values for leases by category in the year the initial lease term ends
2015	856
2016	606
2017	105
2018	19
2019	0
Thereafter	0
Total	1,586
Operating Leases
Residual values for leases by category in the year the initial lease term ends
2015	2,818
2016	7,926
2017	10,332
2018	9,265
2019	7,857
Thereafter	19,050
Total	$57,248

Lease_Investments_Details_4

Lease Investments (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	lease	lease
Lease Investments
Limit on individual lease equipment residual value per transaction	$1,000,000
Number of leases	3,793	3,590
Average residual value per lease	34,000	21,000
Average residual value per master lease	155,000	82,000
Rental income	64,017,000	62,629,000	49,473,000
Equipment maintenance contracts revenue, net of cost of sales	16,441,000	11,071,000	14,129,000
Vendor promotional income	8,382,000	7,587,000	4,051,000
Other lease related revenue	2,121,000	1,796,000	167,000
Gain on sale of lease payments and leased equipment, net of residual write downs	12,899,000	12,002,000	4,708,000
Income on lease investments, gross	103,860,000	95,085,000	72,528,000
Less: depreciation on operating leases	-39,550,000	-33,842,000	-36,146,000
Lease financing, net	$64,310,000	$61,243,000	$36,382,000

Premises_and_Equipment_Details

Premises and Equipment (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Premises and Equipment
Premises and equipment, gross	$352,358	$319,469
Accumulated depreciation	-113,981	-98,404
Premises and equipment, net	238,377	221,065
Depreciation of premises and equipment and leased equipment	20,401	18,051	16,273
Land and land improvements
Premises and Equipment
Premises and equipment, gross	67,630	67,389
Buildings
Premises and Equipment
Premises and equipment, gross	100,505	98,675
Furniture and equipment
Premises and Equipment
Premises and equipment, gross	124,490	97,766
Buildings and leasehold improvements
Premises and Equipment
Premises and equipment, gross	$59,733	$55,639

Goodwill_and_Intangibles_Detai

Goodwill and Intangibles (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 18, 2014
	segment
Acquired Finite-Lived Intangible Assets [Line Items]
Number of operating segments	3
Goodwill impairment loss	$0	$0	$0
Carrying amount of goodwill	711,521,000	423,369,000
Weighted average amortization period (in years)	5 years
Changes in the carrying amount of core deposit and client relationship intangibles
Balance at beginning of period	23,428,000	29,512,000
Amortization expense	-5,501,000	-6,084,000	-5,010,000
Other intangibles from business combinations		0
Balance at end of period	38,006,000	23,428,000	29,512,000
Gross carrying amount	80,371,000	60,292,000
Accumulated amortization	-42,365,000	-36,864,000
Net book value	38,006,000	23,428,000	29,512,000
Estimated future amortization expense
2015	5,963,000
2016	5,157,000
2017	4,637,000
2018	4,221,000
2019	2,743,000
Thereafter	15,285,000
Total estimated future amortization expense	38,006,000
Taylor Capital Group, Inc.
Acquired Finite-Lived Intangible Assets [Line Items]
Carrying amount of goodwill				288,152,000
Goodwill acquired during the period	288,200,000
Taylor Capital Group, Inc. | Core Deposits
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life	15 years
Changes in the carrying amount of core deposit and client relationship intangibles
Other intangibles from business combinations	20,079,000
Banking
Acquired Finite-Lived Intangible Assets [Line Items]
Carrying amount of goodwill	670,881,000
Leasing
Acquired Finite-Lived Intangible Assets [Line Items]
Carrying amount of goodwill	40,640,000
Mortgage Banking
Acquired Finite-Lived Intangible Assets [Line Items]
Carrying amount of goodwill	$0

Deposits_Details

Deposits (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Deposits [Abstract]
Demand deposit accounts, noninterest bearing	$4,118,256,000	$2,375,863,000
NOW and money market accounts	3,913,765,000	2,682,419,000
Savings accounts	940,345,000	855,394,000
Certificates of deposit, $250,000 or more	838,928,000	522,094,000
Other certificates of deposit	1,179,648,000	945,489,000
Total deposits	10,990,942,000	7,381,259,000
Brokered deposits	485,300,000	224,200,000
Scheduled maturities of time certificates
2015	1,595,106,000
2016	204,649,000
2017	96,043,000
2018	29,585,000
2019	38,858,000
Thereafter	54,335,000
Total	$2,018,576,000

ShortTerm_Borrowings_Details

Short-Term Borrowings (Details) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Mar. 09, 2012	Dec. 31, 2013
Short-term borrowings
Weighted Average Cost	0.15%		0.18%
Amount	931,415,000		$493,389,000
Fixed interest rate Federal Home Loan Bank advances	700,000,000		300,000,000
Effective interest rate for fixed rate advance (as a percent)	0.13%
Customer repurchase agreements
Short-term borrowings
Weighted Average Cost	0.21%		0.20%
Amount	219,824,000		193,389,000
Federal Home Loan Bank advances
Short-term borrowings
Weighted Average Cost	0.13%		0.17%
Amount	700,000,000		300,000,000
Federal Funds Purchased
Short-term borrowings
Weighted Average Cost	0.14%		0.00%
Amount	11,591,000		0
Line of Credit
Short-term borrowings
Unsecured line of credit		35,000,000
Description of interest rate basis	one month LIBOR
Line of Credit | Libor
Short-term borrowings
Interest rate, basis spread (as a percent)		1.85%

Longterm_Borrowings_Details

Long-term Borrowings (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Long-term Debt, Unclassified [Abstract]
Federal Home Loan Bank advances	$4,200,000	$4,300,000
Effective interest rates on Federal Home Loan Bank advances, low end of range (as a percent)	3.23%
Effective interest rates on Federal Home Loan Bank advances, high end of range (as a percent)	5.87%
Long-term borrowings
Long-term borrowings	82,916,000	62,159,000
Principal payments due on long-term borrowings
2015	17,589,000
2016	53,147,000
2017	6,018,000
2018	1,917,000
2019	680,000
Thereafter	3,565,000
Total	82,916,000	62,159,000
Notes payable to banks
Long-term borrowings
Long-term borrowings	38,500,000	17,500,000
Minimum interest rates (as a percent)	2.25%
Maximum interest rates (as a percent)	12.00%
Equipment pledged as collateral	48,800,000	25,700,000
Principal payments due on long-term borrowings
Total	38,500,000	17,500,000
Structured repurchase agreement
Long-term borrowings
Long-term borrowings	40,000,000	40,000,000
Term of structured repurchase agreement (in years)	10 years	10 years
Fixed interest rate, if option not exercised (as a percent)	4.75%	4.75%
Principal payments due on long-term borrowings
Total	$40,000,000	$40,000,000

Junior_Subordinated_Notes_Issu2

Junior Subordinated Notes Issued to Capital Trusts (Details) (USD $)	12 Months Ended				0 Months Ended	3 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Sep. 22, 2014	Sep. 30, 2014
Outstanding junior subordinated notes
Principal balance	$185,778		$152,065
Liquidation amount of trust preferred securities	13,059		61,616	156,956
Gain on extinguishment of debt	1,895		0	0
Junior Subordinated Notes | Maximum
Outstanding junior subordinated notes
Period for deferment of payment of interest on notes (in years)	5 years
Taylor Capital Trust I [Member] | Junior Subordinated Notes
Outstanding junior subordinated notes
Stated interest rate					9.75%
Liquidation amount of trust preferred securities					45,400
Gain on extinguishment of debt						1,900
Coal City Capital Trust I | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	25,774
Interest rate, basis spread (as a percent)	1.80%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust II | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	36,083
Interest rate, basis spread (as a percent)	1.40%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust III | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	10,310
Interest rate, basis spread (as a percent)	1.50%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust IV | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	20,619
Interest rate, basis spread (as a percent)	1.52%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust V | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	30,928
Interest rate, basis spread (as a percent)	1.30%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust VI | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	23,196
Interest rate, basis spread (as a percent)	1.30%
Description of annual interest rate basis	3-mo LIBOR
FOBB Statutory Trust III | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	5,155	[1]
Interest rate, basis spread (as a percent)	2.80%	[1]
Description of annual interest rate basis	3-mo LIBOR	[1]
TAYC Capital Trust II [Member] | Junior Subordinated Notes
Outstanding junior subordinated notes
Principal balance	$41,238	[2]
Interest rate, basis spread (as a percent)	2.68%	[2]
Description of annual interest rate basis	3-mo LIBOR	[2]
[1]	FOBB Statutory Trust III was established by First Oak Brook Bancshares, Inc. (“FOBB”) prior to the Company's acquisition of FOBB, and the junior subordinated notes issued by FOBB to FOBB Statutory Trust III were assumed by the Company upon completion of the acquisition.
[2]	TAYC Capital Trust II was established by Taylor Capital prior to the Company's acquisition of Taylor Capital, and the junior subordinated notes issued by Taylor Capital to TAYC Capital Trust II were assumed by the Company upon completion of the acquisition. Principal balance and face value amounts associated with TAYC Capital Trust II do not include purchase accounting adjustments to such amounts, which in each case resulted in a discount of $7.5 million.

Junior_Subordinated_Notes_Issu3

Junior Subordinated Notes Issued to Capital Trusts (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014
Coal City Capital Trust I | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	$25,000,000
Interest rate, basis spread (as a percent)	1.80%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust II | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	35,000,000
Interest rate, basis spread (as a percent)	1.40%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust III | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	10,000,000
Interest rate, basis spread (as a percent)	1.50%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust IV | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	20,000,000
Interest rate, basis spread (as a percent)	1.52%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust V | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	30,000,000
Interest rate, basis spread (as a percent)	1.30%
Description of annual interest rate basis	3-mo LIBOR
MB Financial Capital Trust VI | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	22,500,000
Interest rate, basis spread (as a percent)	1.30%
Description of annual interest rate basis	3-mo LIBOR
FOBB Statutory Trust III | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	5,000,000	[1]
Interest rate, basis spread (as a percent)	2.80%	[1]
Description of annual interest rate basis	3-mo LIBOR	[1]
TAYC Capital Trust II [Member]
Trust preferred securities issued by each trust
Purchase accounting adjustments discount	7,500,000
TAYC Capital Trust II [Member] | Trust preferred securities issued by each trust
Trust preferred securities issued by each trust
Face Value	$40,000,000	[2]
Interest rate, basis spread (as a percent)	2.68%	[2]
Description of annual interest rate basis	3-mo LIBOR	[2]
[1]	FOBB Statutory Trust III was established by First Oak Brook Bancshares, Inc. (“FOBB”) prior to the Company's acquisition of FOBB, and the junior subordinated notes issued by FOBB to FOBB Statutory Trust III were assumed by the Company upon completion of the acquisition.
[2]	TAYC Capital Trust II was established by Taylor Capital prior to the Company's acquisition of Taylor Capital, and the junior subordinated notes issued by Taylor Capital to TAYC Capital Trust II were assumed by the Company upon completion of the acquisition. Principal balance and face value amounts associated with TAYC Capital Trust II do not include purchase accounting adjustments to such amounts, which in each case resulted in a discount of $7.5 million.

Lease_Commitments_and_Rental_E2

Lease Commitments and Rental Expense (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Rents
Net rental expense	$7,400,000	$4,700,000	$5,400,000
Office space
Gross Rents
2015	10,272,000
2016	8,329,000
2017	7,398,000
2018	5,296,000
2019	4,680,000
Thereafter	17,310,000
Total	53,285,000
Sublease Rents
2015	797,000
2016	484,000
2017	439,000
2018	414,000
2019	424,000
Thereafter	581,000
Total	3,139,000
Net Rents
2015	9,475,000
2016	7,845,000
2017	6,959,000
2018	4,882,000
2019	4,256,000
Thereafter	16,729,000
Total	$50,146,000

Employee_Benefit_Plans_Details

Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Benefit Plans
Requisite service period to participate in contribution plan (in months)	3 months
Employee contribution limit per calendar year (as a percent of compensation)	75.00%
Employer contribution limit per calendar year (as a percent of compensation)	3.50%
Company's expected contribution to plan during current fiscal year	$8,600,000
Company's total contribution to plan		7,000,000	6,900,000
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defer payment, participant limit per calendar year (as a percent of compensation)	100.00%
Estimated discretionary company contributions	563,000
Actual employer's contribution		643,000	464,000
Chief executive officer | Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Employer's contribution to deferred compensation plan (as a percent of base salary)	20.00%
Fair market value of assets held in other publicly traded funds	16,800,000
Decreases in fair market value of assets and obligation	$829,000

Income_Taxes_Details

Income Taxes (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax asset:
Allowance for credit losses	$43,853	$44,418
Federal net operating loss carryforwards	12,234	0
State net operating loss carryforwards	26,582	24,354
Other real estate owned	14,229	7,878
Stock options and restricted stock	5,904	5,816
Loans	47,668	6,833
Deferred compensation	10,620	8,423
Tax credit carryforwards	25,244	13,233
Bonus accrual	5,595	4,739
Merger and non-compete accrual	0	623
Other items	3,390	1,222
Total deferred tax asset	195,319	117,539
Valuation allowance	0	0
Total deferred tax asset, net of valuation allowance	195,319	117,539
Deferred tax liability:
Equipment leasing	-112,524	-90,941
Premises and equipment	-18,817	-27,059
Mortgage servicing rights	-64,486	-7
Deferred income from FDIC-assisted transactions	-45,999	-48,272
Investment securities	-1,802	-5,030
FHLB stock dividends	-2,652	-2,441
Core deposit intangible	-9,118	-2,918
Other items	-2,794	-3,792
Total deferred tax liability	-258,192	-180,460
Net deferred tax liability	-62,873	-62,921
Net unrealized holding gain on investment securities available for sale	-13,099	-5,354
Net deferred tax liability	($75,972)	($68,275)

Income_Taxes_Details_2

Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current expense (benefit):
Federal	$25,270,000	$12,234,000	$15,075,000
State	11,971,000	5,576,000	6,225,000
Foreign	0	0	0
Current expense (benefit)	37,241,000	17,810,000	21,300,000
Deferred expense (benefit):
Federal	3,122,000	17,245,000	13,688,000
State	-3,170,000	4,436,000	1,489,000
Foreign	0	0	0
Deferred income tax expense	-48,000	21,681,000	15,177,000
Income tax expense	37,193,000	39,491,000	36,477,000
Statutory federal income tax rate (as a percent)	35.00%
Federal income tax expense at expected statutory rate	43,153,000	48,281,000	44,398,000
Increase (decrease) due to:
Tax exempt income, net	-14,848,000	-14,200,000	-12,539,000
State tax expense net of federal impact	5,721,000	6,508,000	5,014,000
Non-deductible contingent consideration	3,738,000	0	0
Non-includable increase in cash surrender value of life insurance	-1,120,000	-1,111,000	-1,177,000
Non-deductible merger expense	988,000	591,000	0
Adjustment of tax contingency reserves	-31,000	-24,000	14,000
Other items, net	-408,000	-554,000	767,000
Income tax expense	37,193,000	39,491,000	36,477,000
Federal Alternative Minimum Tax Credit Carryforward
Operating loss carryforwards
Tax credit carryforward	21,400,000
General Business Tax Credit Carryforward
Operating loss carryforwards
Tax credit carryforward	3,700,000
Domestic Tax Authority [Member]
Operating loss carryforwards
Net operating loss carryforwards	35,000,000
State
Operating loss carryforwards
Net operating loss carryforwards	12,700,000
ILLINOIS | State
Operating loss carryforwards
Net operating loss carryforwards	$509,200,000

Income_Taxes_Details_3

Income Taxes (Details 3) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Unrecognized Tax Benefit Without Interest
Balance at the beginning of the period	$73
Increases for tax positions of prior years	0
Acquisition related increases	939
Benefits recognized	-31
Balance at the end of the period	981
Interest on unrecognized Tax Benefit
Balance at the beginning of the period	7
Increases for tax positions of prior years	6
Acquisition related increases	0
Benefits recognized	-6
Balance at the end of the period	7
Total Unrecognized Tax Benefit Including Interest
Balance at the beginning of the period	80
Increases for tax positions of prior years	6
Acquisition related increases	939
Benefits recognized	-37
Balance at the end of the period	$988

Commitments_and_Contingencies_1

Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Commitments [Abstract]
Maximum maturity period for letters of credit (in years)	5 years
Increase in maximum potential amount of future payments under letters of credit	$63,900,000
Dollar amount of letters of credit outstanding	134,200,000	70,300,000
Letters of credit issued or renewed		121,800,000
Capital expenditure commitments outstanding	1,400,000
Home equity lines
Commitments and contingencies
Dollar amount of line of credit outstanding	221,102,000	208,581,000
Other commitments
Commitments and contingencies
Dollar amount of line of credit outstanding	2,643,220,000	1,214,391,000
Standby
Commitments and contingencies
Dollar amount of line of credit outstanding	131,810,000	69,556,000
Commercial
Commitments and contingencies
Dollar amount of line of credit outstanding	$2,401,000	$708,000

Commitments_and_Contingencies_2

Commitments and Contingencies (Details 2) (States and political subdivisions, State of Illinois)	12 Months Ended
	Dec. 31, 2014
States and political subdivisions | State of Illinois
Concentrations of credit risk
Percentage of investments issued by states and political subdivisions that were within the state of Illinois	27.00%

Regulatory_Matters_Details

Regulatory Matters (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Total capital (to risk-weighted assets):
Actual Amount	$1,544,759	$1,106,541
Actual Ratio (as a percent)	13.62%	16.53%
For Capital Adequacy Purposes Amount	907,369	535,430
For Capital Adequacy Purposes Ratio (as a percent)	8.00%	8.00%
Tier I capital (to risk-weighted assets):
Actual Amount	1,430,702	1,022,512
Actual Ratio (as a percent)	12.61%	15.28%
For Capital Adequacy Purposes Amount	453,684	267,715
For Capital Adequacy Purposes Ratio (as a percent)	4.00%	4.00%
Tier I capital (to average assets):
Actual Amount	1,430,702	1,022,512
Actual Ratio (as a percent)	10.47%	11.22%
For Capital Adequacy Purposes Amount	546,766	364,587
For Capital Adequacy Purposes Ratio (as a percent)	4.00%	4.00%
MB Financial Bank
Total capital (to risk-weighted assets):
Actual Amount	1,473,928	974,189
Actual Ratio (as a percent)	13.03%	14.59%
For Capital Adequacy Purposes Amount	904,917	534,004
For Capital Adequacy Purposes Ratio (as a percent)	8.00%	8.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,131,146	667,505
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)	10.00%	10.00%
Tier I capital (to risk-weighted assets):
Actual Amount	1,359,871	890,380
Actual Ratio (as a percent)	12.02%	13.34%
For Capital Adequacy Purposes Amount	452,459	267,002
For Capital Adequacy Purposes Ratio (as a percent)	4.00%	4.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	678,688	400,503
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)	6.00%	6.00%
Tier I capital (to average assets):
Actual Amount	1,359,871	890,380
Actual Ratio (as a percent)	9.96%	9.79%
For Capital Adequacy Purposes Amount	545,943	363,904
For Capital Adequacy Purposes Ratio (as a percent)	4.00%	4.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$682,429	$454,880
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)	5.00%	5.00%

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Financial assets
Securities available for sale, at fair value	$1,654,752,000		$1,118,912,000
Loans held for sale	737,209,000		629,000
Mortgage servicing rights, at fair value	235,402,000		413,000
Derivative financial instruments, assets	13,952,000		5,875,000
Financial liabilities
Derivative financial instrument, liabilities	37,927,000		12,753,000
U.S. Government sponsored agencies and enterprises
Financial assets
Securities available for sale, at fair value	65,873,000		52,068,000
States and political subdivisions
Financial assets
Securities available for sale, at fair value	410,854,000		19,143,000
Residential mortgage-backed securities
Financial assets
Securities available for sale, at fair value	720,563,000		701,233,000
Commercial mortgage-backed securities
Financial assets
Securities available for sale, at fair value	187,662,000		52,941,000
Corporate bonds
Financial assets
Securities available for sale, at fair value	259,203,000		283,070,000
Equity securities
Financial assets
Securities available for sale, at fair value	10,597,000		10,457,000
Recurring basis
Financial assets
Loans held for sale	737,209,000		629,000
Mortgage servicing rights, at fair value	235,402,000
Assets held in trust for deferred compensation	16,829,000		10,679,000
Derivative financial instruments, assets	46,388,000		18,645,000
Financial liabilities
Other liabilities	16,483,000	[1]	10,569,000	[1]
Derivative financial instrument, liabilities	40,499,000		18,632,000
Recurring basis | U.S. Government sponsored agencies and enterprises
Financial assets
Securities available for sale, at fair value	65,873,000		52,068,000
Recurring basis | States and political subdivisions
Financial assets
Securities available for sale, at fair value	410,854,000		19,143,000
Recurring basis | Residential mortgage-backed securities
Financial assets
Securities available for sale, at fair value	720,563,000		701,233,000
Recurring basis | Commercial mortgage-backed securities
Financial assets
Securities available for sale, at fair value	187,662,000		52,941,000
Recurring basis | Corporate bonds
Financial assets
Securities available for sale, at fair value	259,203,000		283,070,000
Recurring basis | Equity securities
Financial assets
Securities available for sale, at fair value	10,597,000		10,457,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets
Securities available for sale, at fair value	10,597,000		10,457,000
Loans held for sale	0		0
Mortgage servicing rights, at fair value	0
Assets held in trust for deferred compensation	16,829,000		10,679,000
Derivative financial instruments, assets	1,607,000		0
Financial liabilities
Other liabilities	16,483,000	[1]	10,569,000	[1]
Derivative financial instrument, liabilities	7,209,000		0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government sponsored agencies and enterprises
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | States and political subdivisions
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential mortgage-backed securities
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial mortgage-backed securities
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Financial assets
Securities available for sale, at fair value	10,597,000		10,457,000
Recurring basis | Significant Other Observable Inputs (Level 2)
Financial assets
Securities available for sale, at fair value	1,643,182,000		1,102,599,000
Loans held for sale	737,209,000		629,000
Mortgage servicing rights, at fair value	0
Assets held in trust for deferred compensation	0		0
Derivative financial instruments, assets	39,707,000		18,645,000
Financial liabilities
Other liabilities	0	[1]	0	[1]
Derivative financial instrument, liabilities	33,290,000		18,632,000
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government sponsored agencies and enterprises
Financial assets
Securities available for sale, at fair value	65,873,000		52,068,000
Recurring basis | Significant Other Observable Inputs (Level 2) | States and political subdivisions
Financial assets
Securities available for sale, at fair value	410,391,000		19,143,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Financial assets
Securities available for sale, at fair value	720,053,000		700,542,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Commercial mortgage-backed securities
Financial assets
Securities available for sale, at fair value	187,662,000		52,941,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate bonds
Financial assets
Securities available for sale, at fair value	259,203,000		277,905,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Equity securities
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Significant Unobservable Inputs (Level 3)
Financial assets
Securities available for sale, at fair value	973,000		5,856,000
Loans held for sale	0		0
Mortgage servicing rights, at fair value	235,402,000
Assets held in trust for deferred compensation	0		0
Derivative financial instruments, assets	5,074,000		0
Financial liabilities
Other liabilities	0	[1]	0	[1]
Derivative financial instrument, liabilities	0		0
Recurring basis | Significant Unobservable Inputs (Level 3) | U.S. Government sponsored agencies and enterprises
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Significant Unobservable Inputs (Level 3) | States and political subdivisions
Financial assets
Securities available for sale, at fair value	463,000		0
Recurring basis | Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities
Financial assets
Securities available for sale, at fair value	510,000		691,000
Recurring basis | Significant Unobservable Inputs (Level 3) | Commercial mortgage-backed securities
Financial assets
Securities available for sale, at fair value	0		0
Recurring basis | Significant Unobservable Inputs (Level 3) | Corporate bonds
Financial assets
Securities available for sale, at fair value	0		5,165,000
Recurring basis | Significant Unobservable Inputs (Level 3) | Equity securities
Financial assets
Securities available for sale, at fair value	$0		$0
[1]	Liabilities associated with assets held in trust for deferred compensation

Fair_Value_Measurements_Detail1

Fair Value Measurements (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	$1,654,752,000	$1,118,912,000
Mortgage servicing rights, at fair value	235,402,000	413,000
Derivative financial instruments, assets	13,952,000	5,875,000
Appraisal adjustments - sales costs (as a percent)	90.00%
States and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	410,854,000	19,143,000
Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	720,563,000	701,233,000
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	259,203,000	283,070,000
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Mortgage servicing rights, at fair value	235,402,000
Derivative financial instruments, assets	46,388,000	18,645,000
Recurring basis | States and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	410,854,000	19,143,000
Recurring basis | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	720,563,000	701,233,000
Recurring basis | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	259,203,000	283,070,000
Significant Unobservable Inputs (Level 3) | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	973,000	5,856,000
Mortgage servicing rights, at fair value	235,402,000
Derivative financial instruments, assets	5,074,000	0
Significant Unobservable Inputs (Level 3) | Recurring basis | States and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	463,000	0
Credit assumption (as a percent)	45.00%
Significant Unobservable Inputs (Level 3) | Recurring basis | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	510,000	691,000
Significant Unobservable Inputs (Level 3) | Recurring basis | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	0	5,165,000
Significant Unobservable Inputs (Level 3) | Recurring basis | Minimum | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Constant prepayment rates (as a percent)	1.00%
Significant Unobservable Inputs (Level 3) | Recurring basis | Minimum | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
CPR (as percent)	4.90%
Discount rate (as percent)	9.25%
Maturity period (in months)	36 months
Delinquencies (as percent)	0.00%
Costs to service	60
Significant Unobservable Inputs (Level 3) | Recurring basis | Minimum | Mortgage Derivative Instruments
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Expected closing ratio	16.90%
Expected delivery price	98.89%
Significant Unobservable Inputs (Level 3) | Recurring basis | Maximum | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Constant prepayment rates (as a percent)	3.00%
Significant Unobservable Inputs (Level 3) | Recurring basis | Maximum | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
CPR (as percent)	26.90%
Discount rate (as percent)	16.00%
Maturity period (in months)	460 months
Delinquencies (as percent)	28.57%
Costs to service	$356
Significant Unobservable Inputs (Level 3) | Recurring basis | Maximum | Mortgage Derivative Instruments
Fair Value, Assets and Liabilities Measured on Recurring and a Nonrecurring Basis [Line Items]
Expected closing ratio	94.00%
Expected delivery price	1.10%

Fair_Value_Measurements_Detail2

Fair Value Measurements (Details 3) (Mortgage Servicing Rights, USD $)	12 Months Ended
	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
CPR, Impact on fair value of 10% adverse change	($9,650,000)
CPR, Impact on fair value of 20% adverse change	-18,574,000
Discount rate, Impact on fair value of 10% adverse change	-8,998,000
Discount rate, Impact on fair value of 20% adverse change	-17,356,000
Delinquency rate, Impact on fair value of 10% adverse change	-1,520,000
Delinquency rate, Impact on fair value of 20% adverse change	-2,196,000
Weighted average costs to service, Impact on fair value of 10% adverse change	-3,325,000
Weighted average costs to service, Impact on fair value of 20% adverse change	-6,651,000
Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
CPR (as percent)	11.50%
Discount rate (as percent)	9.41%
Delinquencies (as percent)	1.25%
Costs to service	$70

Fair_Value_Measurements_Detail3

Fair Value Measurements (Details 4) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the end of the period	$973	$5,856
Securities Investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	5,856	6,071
Acquired through business combination	507	0
Purchases	0	0
Originations	0	0
Other comprehensive income	128	-44
Principal payments	-363	-157
Impairment charge	-92	-14
Sales	-498	0
Transferred out of level 3	-4,565	0
Balance at the end of the period		5,856
Mortgage Servicing Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	0	0
Acquired through business combination	224,798	0
Purchases	1,096	0
Originations	21,285	0
Other comprehensive income	-11,777	0
Principal payments	0	0
Transferred out of level 3	0	0
Balance at the end of the period	235,402	0
Mortgage Derivative Instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	0	0
Acquired through business combination	5,922	0
Purchases	0	0
Originations	0	0
Other comprehensive income	-848	0
Principal payments	0	0
Transferred out of level 3	0	0
Balance at the end of the period	5,074	0
Recurring basis | Significant Unobservable Inputs (Level 3) | Mortgage Servicing Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Impairment charge	0	0
Sales	0	0
Recurring basis | Significant Unobservable Inputs (Level 3) | Mortgage Derivative Instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Impairment charge	0	0
Sales	$0	$0

Fair_Value_Measurements_Detail4

Fair Value Measurements (Details 5) (Nonrecurring basis, USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financial Assets:
Impaired loans	$61,717	$77,497
Foreclosed assets	38,619	44,601
Significant Unobservable Inputs (Level 3)
Financial Assets:
Impaired loans	61,717	77,497
Foreclosed assets	$38,619	$44,601
Significant Unobservable Inputs (Level 3) | Minimum
Financial Assets:
Appraisal adjustment, impaired loans	5.00%
Appraisal adjustment, foreclosed assets	5.00%
Significant Unobservable Inputs (Level 3) | Maximum
Financial Assets:
Appraisal adjustment, impaired loans	10.00%
Appraisal adjustment, foreclosed assets	10.00%

Fair_Value_Measurements_Detail5

Fair Value Measurements (Details 6) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Maximum maturity period of short-term borrowings where carrying value approximates fair value (in days)	90 days
Minimum maturity period of short-term borrowings where fair value is based on discounted value of contractual cash flows (in days)	90 days
Financial Assets:
Cash and due from banks	$256,804	$205,193
Interest bearing deposits with banks	55,277	268,266
Federal funds sold	0	42,950
Securities available for sale, at fair value	1,654,752	1,118,912
Investment securities held to maturity	1,035,061	1,198,929
Non-marketable securities - FHLB and FRB stock	75,569	51,417
Loans held for sale	737,209	629
Derivative financial instruments	13,952	5,875
Financial Liabilities:
Non-interest bearing deposits	4,118,256	2,375,863
Interest bearing deposits	6,872,686	5,005,396
Short-term borrowings	931,415	493,389
Junior subordinated notes issued to capital trusts	185,778	152,065
Derivative financial instruments	37,927	12,753
Carrying Amount
Financial Assets:
Cash and due from banks	256,804	205,193
Interest bearing deposits with banks	55,277	268,266
Federal funds sold		42,950
Securities available for sale, at fair value	1,654,752	1,118,912
Investment securities held to maturity	993,380	1,182,533
Non-marketable securities - FHLB and FRB stock	75,569	51,417
Loans held for sale	737,209	629
Loans, net	8,973,191	5,600,805
Accrued interest receivable	49,065	36,593
Derivative financial instruments	46,388	18,645
Financial Liabilities:
Non-interest bearing deposits	4,118,256	2,375,863
Interest bearing deposits	6,872,686	5,005,396
Short-term borrowings	931,415	493,389
Long-term borrowings	82,916	62,159
Junior subordinated notes issued to capital trusts	185,778	152,065
Accrued interest payable	3,709	2,042
Derivative financial instruments	40,499	18,632
Total Fair Value
Financial Assets:
Cash and due from banks	256,804	205,193
Interest bearing deposits with banks	55,277	268,266
Federal funds sold		42,950
Securities available for sale, at fair value	1,654,752	1,118,912
Investment securities held to maturity	1,035,061	1,198,929
Non-marketable securities - FHLB and FRB stock	75,569	51,417
Loans held for sale	737,209	629
Loans, net	8,956,494	5,583,759
Accrued interest receivable	49,065	36,593
Derivative financial instruments	46,388	18,645
Financial Liabilities:
Non-interest bearing deposits	4,118,256	2,375,863
Interest bearing deposits	6,877,349	5,012,928
Short-term borrowings	931,416	493,384
Long-term borrowings	86,025	66,301
Junior subordinated notes issued to capital trusts	122,408	101,247
Accrued interest payable	3,709	2,042
Derivative financial instruments	40,499	18,632
Recurring basis
Financial Assets:
Loans held for sale	737,209	629
Derivative financial instruments	46,388	18,645
Financial Liabilities:
Derivative financial instruments	40,499	18,632
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and due from banks	256,804	205,193
Interest bearing deposits with banks	55,277	268,266
Federal funds sold		42,950
Securities available for sale, at fair value	10,597	10,457
Investment securities held to maturity	0	0
Non-marketable securities - FHLB and FRB stock	0	0
Loans held for sale	0	0
Loans, net	0	0
Accrued interest receivable	49,065	36,593
Derivative financial instruments	1,607	0
Financial Liabilities:
Non-interest bearing deposits	4,118,256	2,375,863
Interest bearing deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Junior subordinated notes issued to capital trusts	0	0
Accrued interest payable	3,709	2,042
Derivative financial instruments	7,209	0
Recurring basis | Significant Other Observable Inputs (Level 2)
Financial Assets:
Cash and due from banks	0	0
Interest bearing deposits with banks	0	0
Federal funds sold		0
Securities available for sale, at fair value	1,643,182	1,102,599
Investment securities held to maturity	1,035,061	1,198,929
Non-marketable securities - FHLB and FRB stock	0	0
Loans held for sale	737,209	629
Loans, net	0	0
Accrued interest receivable	0	0
Derivative financial instruments	39,707	18,645
Financial Liabilities:
Non-interest bearing deposits	0	0
Interest bearing deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Junior subordinated notes issued to capital trusts	0	0
Accrued interest payable	0	0
Derivative financial instruments	33,290	18,632
Recurring basis | Significant Unobservable Inputs (Level 3)
Financial Assets:
Cash and due from banks	0	0
Interest bearing deposits with banks	0	0
Federal funds sold		0
Securities available for sale, at fair value	973	5,856
Investment securities held to maturity	0	0
Non-marketable securities - FHLB and FRB stock	75,569	51,417
Loans held for sale	0	0
Loans, net	8,956,494	5,583,759
Accrued interest receivable	0	0
Derivative financial instruments	5,074	0
Financial Liabilities:
Non-interest bearing deposits	0	0
Interest bearing deposits	6,877,349	5,012,928
Short-term borrowings	931,416	493,384
Long-term borrowings	86,025	66,301
Junior subordinated notes issued to capital trusts	122,408	101,247
Accrued interest payable	0	0
Derivative financial instruments	$0	$0

Stock_Incentive_Plans_Details

Stock Incentive Plans (Details) (USD $)	12 Months Ended			0 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	28-May-14	Dec. 31, 2011
Impact of the share-based payment plans in the financial statements
Total cost of share-based payment plans during the year	$8,974,000	$5,456,000	$4,806,000
Amount of related income tax benefit recognized in income	3,528,000	2,159,000	1,918,000
Stock-based compensation
Numerator of shares granted beyond threshold limit	2
Denominator of shares granted beyond threshold limit	1
Omnibus Incentive Plan (the "Omnibus Plan")
Stock-based compensation
Number of additional authorized shares				3,100,000
Number of common shares authorized for issuance				11,400,000
Percentage of shares authorized for issuance				10.00%
Number of shares available for future grants	6,243,194
Minimum vesting period (in years)				3 years
Unrecognized compensation cost	$17,400,000
Expected weighted-average period for recognition of unrecognized compensation expense (in years)	2 years 3 months 0 days
Stock options
Stock-based compensation
Continuous service period for vesting of option awards (in years)	4 years
Contractual terms of option awards (in years)	10 years
Stock options | Director
Stock-based compensation
Minimum vesting period (in years)	5 years
Maximum percentage of fees with an option to be received in equity-based incentive awards	70.00%
Period of restriction for sale of underlying shares (in months)	6 months
Restricted stock | Director
Stock-based compensation
Minimum vesting period (in years)	1 year
Maximum percentage of fees with an option to be received in equity-based incentive awards	100.00%
Performance-based restricted stock units
Stock-based compensation
Minimum vesting period (in years)	3 years
Number of shares issued	48,569	56,752	65,333
Performance based restricted units performance period (in years)	3 years
Share based compensation restricted stock units multiplier (in percent)	100.00%
Market-based restricted stock
Stock-based compensation
Number of shares issued					92,717
Number of consecutive trading days over which a specified closing price of the entity's stock is maintained					10 days
Minimum closing price of the entity's stock (in dollars per share)					$27
Minimum | Restricted stock and restricted stock units
Stock-based compensation
Minimum vesting period (in years)	2 years
Minimum | Performance-based restricted stock units
Stock-based compensation
Percentage of shares earned to number of units issued	0.00%
Maximum | Restricted stock and restricted stock units
Stock-based compensation
Minimum vesting period (in years)	4 years
Maximum | Performance-based restricted stock units
Stock-based compensation
Percentage of shares earned to number of units issued	175.00%
Taylor Capital Group, Inc. | Omnibus Incentive Plan (the "Omnibus Plan")
Stock-based compensation
Number of common shares authorized for issuance	13,800,000
Number of additional shares authorized				2,400,000

Stock_Incentive_Plans_Details_

Stock Incentive Plans (Details 2) (Stock options, USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Stock options
Options outstanding activity
Options outstanding at the beginning of the period (in shares)	2,443,752
Granted (in shares)	231,977
Exercised (in shares)	-211,339
Expired or cancelled (in shares)	-177,125
Forfeited (in shares)	-36,551
Options outstanding at the end of the period (in shares)	2,250,714	2,443,752
Weighted Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)	$27.57
Granted (in dollars per share)	$29.63
Exercised (in dollars per share)	$19.88
Expired or cancelled (in dollars per share)	$35.78
Forfeited (in dollars per share)	$22.33
Options outstanding at the end of the period (in dollars per share)	$27.94	$27.57
Options exercisable at end of the period (in dollars per share)	$29
Options exercisable at end of the period (in shares)	1,689,055
Weighted Average Remaining Contractual Term (In Years)
Options outstanding at the end of the period	4 years 4 months 20 days	4 years 8 months 16 days
Options exercisable at end of the period	3 years 2 months 12 days
Aggregate Intrinsic Value
Options outstanding at the end of the period	$13,820
Options exercisable at end of the period	$9,263

Stock_Incentive_Plans_Details_1

Stock Incentive Plans (Details 3) (Stock options, USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock options
Stock-based compensation
Intrinsic value of options exercised	$2,000	$1,300	$203
Fair value assumptions
Risk free interest rate (as a percent)	1.82%	1.92%	1.02%
Expected volatility of Company's stock (as a percent)	23.16%	25.18%	27.17%
Expected dividend yield (as a percent)	1.65%	1.73%	2.00%
Expected life of options (in years)	5 years 6 months 10 days	5 years 6 months 19 days	5 years 8 months 12 days
Weighted average fair value per option of options granted during the year (in dollars per share)	$5.93	$5.88	$4.23

Stock_Incentive_Plans_Details_2

Stock Incentive Plans (Details 4) (Restricted stock and restricted stock units, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted stock and restricted stock units
Stock-based compensation
Intrinsic value of restricted shares vested	$8,600,000	$5,800,000	$6,200,000
Changes in restricted shares
Nonvested shares of restricted stock and nonvested restricted stock units at the beginning of the period	685,719
Granted (in shares)	443,375
Vested (in shares)	-305,504
Forfeited (in shares)	-22,505
Nonvested shares of restricted stock and nonvested restricted stock units at the end of the period	801,085	685,719
Weighted Average Grant Date Fair Value, restricted shares
Shares Outstanding at the beginning of the period (in dollars per share)	$22.59
Granted (in dollars per share)	$29.23
Vested (in dollars per share)	$20.53
Forfeited (in dollars per share)	$24.92
Nonvested shares of restricted stock and nonvested restricted stock units at the end of the period (in dollars per share)	$26.99	$22.59

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Net amount payable under interest rate swap	$1,134,000		$25,000
Interest rate swap credit risk exposure	11,200,000
Asset Derivatives, Notional Amount	2,465,120,000		667,934,000
Derivative Asset	46,388,000		18,645,000
Asset Derivatives, Estimated Fair Value	13,952,000		5,875,000
Liability Derivatives, Notional Amount	2,964,961,000		684,999,000
Derivative Liability	-40,499,000		-18,632,000
Liability Derivatives, Estimated Fair Value	-37,927,000		-12,753,000
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	1,583,000		-90,000		178,000
Stand-alone derivative instruments
Derivative [Line Items]
Asset Derivatives, Notional Amount	2,465,120,000	[1]	667,934,000	[1]
Derivative Asset	46,388,000	[1]	18,645,000	[1]
Liability Derivatives, Notional Amount	2,964,764,000	[1]	684,761,000	[1]
Derivative Liability	-40,484,000	[1]	-18,609,000	[1]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	1,575,000		-99,000		193,000
Commercial loan interest rate swaps
Derivative [Line Items]
Liability Derivatives, Notional Amount	197,000
Interest rate swap contracts | Derivative instruments designated as hedges of fair value
Derivative [Line Items]
Liability Derivatives, Notional Amount	197,000	[2]	238,000	[2]
Derivative Liability	-15,000	[2]	-23,000	[2]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	8,000		9,000		-15,000
Interest rate swap contracts | Stand-alone derivative instruments
Derivative [Line Items]
Asset Derivatives, Notional Amount	1,509,930,000	[1]	550,883,000	[1]
Derivative Asset	37,039,000	[1]	17,298,000	[1]
Liability Derivatives, Notional Amount	2,001,787,000	[1]	551,798,000	[1]
Derivative Liability	-30,761,000	[1]	-17,350,000	[1]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	2,458,000		40,000		30,000
Interest rate options contracts | Stand-alone derivative instruments
Derivative [Line Items]
Asset Derivatives, Notional Amount	55,830,000	[1]	83,907,000	[1]
Derivative Asset	283,000	[1]	323,000	[1]
Liability Derivatives, Notional Amount	55,830,000	[1]	84,953,000	[1]
Derivative Liability	-283,000	[1]	-323,000	[1]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	0		0		0
Foreign exchange contracts | Stand-alone derivative instruments
Derivative [Line Items]
Asset Derivatives, Notional Amount	27,402,000	[1]	31,361,000	[1]
Derivative Asset	2,276,000	[1]	1,006,000	[1]
Liability Derivatives, Notional Amount	27,002,000	[1]	47,760,000	[1]
Derivative Liability	-2,109,000	[1]	-935,000	[1]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	96,000		-30,000		67,000
Spot Foreign Exchange Contract [Member] | Stand-alone derivative instruments
Derivative [Line Items]
Asset Derivatives, Notional Amount	512,000		0
Derivative Asset	5,000		0
Liability Derivatives, Notional Amount	304,000		0
Derivative Liability	-18,000		0
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	-14,000		0		0
Mortgage banking derivatives | Stand-alone derivative instruments
Derivative [Line Items]
Asset Derivatives, Notional Amount	871,446,000	[1]	1,783,000	[1]
Derivative Asset	6,785,000	[1]	18,000	[1]
Liability Derivatives, Notional Amount	879,841,000	[1]	250,000	[1]
Derivative Liability	-7,313,000	[1]	-1,000	[1]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amounts of gain or (loss) recognized in income on derivatives	($965,000)		($109,000)		$96,000
[1]	These portfolio swaps are not designated as hedging instruments under ASC Topic 815.
[2]	Hedged fixed-rate commercial real estate loans

Derivative_Financial_Instrumen3

Derivative Financial Instruments (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Derivative [Line Items]
Financial Assets, Gross Amount Recognized	$13,952	$5,875
Financial Assets, Gross Amount Offset	0	0
Financial Assets, Net Amount Recognized	13,952	5,875
Financial Liabilities, Gross Amount Recognized	37,927	12,753
Financial Liabilities, Gross Amount Offset	0	0
Financial Liabilities, Net Amount Recognized	37,927	12,753
Repurchase Agreements, Financial Assets, Gross Amount Recognized	0	0
Repurchase Agreements, Financial Liabilities, Gross Amount Offset	0	0
Repurchase Agreements, Financial Assets, Net Amount Recognized	0	0
Repurchase Agreements, Financial Liabilities, Gross Amount Recognized	219,824	193,389
Repurchase Agreements, Financial Liabilities, Gross Amount Offset	0	0
Repurchase Agreements, Financial Liabilities, Net Amount Recognized	219,824	193,389
Total Financial Assets, Gross Amount Recognized	13,952	5,875
Total Financial Assets, Gross Amount Offset	0	0
Total Financial Assets, Net Amount Recognized	13,952	5,875
Total Financial Liabilities, Gross Amount Recognized	257,751	206,142
Total Financial Liabilities, Gross Amount Offset	0	0
Total Financial Liabilities, Net Amount Recognized	257,751	206,142
Interest rate swaps, caps and floors
Derivative [Line Items]
Financial Assets, Gross Amount Recognized	10,727	5,792
Financial Assets, Gross Amount Offset	0	0
Financial Assets, Net Amount Recognized	10,727	5,792
Financial Liabilities, Gross Amount Recognized	29,916	11,904
Financial Liabilities, Gross Amount Offset	0	0
Financial Liabilities, Net Amount Recognized	29,916	11,904
Foreign currency forward contracts
Derivative [Line Items]
Financial Assets, Gross Amount Recognized	1,525	80
Financial Assets, Gross Amount Offset	0	0
Financial Assets, Net Amount Recognized	1,525	80
Financial Liabilities, Gross Amount Recognized	709	848
Financial Liabilities, Gross Amount Offset	0	0
Financial Liabilities, Net Amount Recognized	709	848
Mortgage banking derivatives
Derivative [Line Items]
Financial Assets, Gross Amount Recognized	1,700	3
Financial Assets, Gross Amount Offset	0	0
Financial Assets, Net Amount Recognized	1,700	3
Financial Liabilities, Gross Amount Recognized	7,302	1
Financial Liabilities, Gross Amount Offset	0	0
Financial Liabilities, Net Amount Recognized	$7,302	$1

Derivative_Financial_Instrumen4

Derivative Financial Instruments (Details 3) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Derivative [Line Items]
Financial Assets, Net Amount Recognized	$13,952	$5,875
Financial Assets, Financial Instruments	-10,201	-2,912
Financial Assets, Collateral	0	0
Financial Assets, Net Amount	3,751	2,963
Financial Liabilities, Net Amount Recognized	37,927	12,753
Financial Liabilities, Financial Instruments	-10,200	-2,912
Financial Liabilities, Collateral	-26,010	-9,786
Financial Liabilities, Net Amount	1,717	55
Repurchase Agreements, Financial Assets, Net Amount Recognized	0	0
Repurchase Agreements, Financial Assets, Financial Instruments	0	0
Repurchase Agreements, Financial Assets, Collateral	0	0
Repurchase Agreements, Financial Assets, Net Amount	0	0
Repurchase Agreements, Financial Liabilities, Net Amount Recognized	219,824	193,389
Repurchase Agreements, Financial Liabilities, Financial Instruments	0	0
Repurchase Agreements, Financial Liabilities, Collateral	-219,824	-193,389
Repurchase Agreements, Financial Liabilities, Net Amount	0	0
Total Financial Assets, Net Amount Recognized	13,952	5,875
Total Financial Assets, Financial Instruments	-10,201	-2,912
Total Financial Assets, Collateral	0	0
Total Financial Assets, Net Amount	3,751	2,963
Total Financial Liabilities, Net Amount Recognized	257,751	206,142
Total Financial Liabilities, Financial Instruments	-10,200	-2,912
Total Financial Liabilities, Collateral	-245,834	-203,175
Total Financial Liabilities, Net Amount	1,717	55
Counterparty A
Derivative [Line Items]
Financial Assets, Net Amount Recognized	13	883
Financial Assets, Financial Instruments	-13	-883
Financial Assets, Collateral	0	0
Financial Assets, Net Amount	0	0
Financial Liabilities, Net Amount Recognized	9,556	10,669
Financial Liabilities, Financial Instruments	-13	-883
Financial Liabilities, Collateral	-9,543	-9,786
Financial Liabilities, Net Amount	0	0
Counterparty B
Derivative [Line Items]
Financial Assets, Net Amount Recognized	145	1,836
Financial Assets, Financial Instruments	-145	-412
Financial Assets, Collateral	0	0
Financial Assets, Net Amount	0	1,424
Financial Liabilities, Net Amount Recognized	3,736	412
Financial Liabilities, Financial Instruments	-145	-412
Financial Liabilities, Collateral	-3,591	0
Financial Liabilities, Net Amount	0	0
Counterparty C
Derivative [Line Items]
Financial Assets, Net Amount Recognized	6,123	2,380
Financial Assets, Financial Instruments	-6,123	-1,612
Financial Assets, Collateral	0	0
Financial Assets, Net Amount	0	768
Financial Liabilities, Net Amount Recognized	10,335	1,612
Financial Liabilities, Financial Instruments	-6,122	-1,612
Financial Liabilities, Collateral	-4,213	0
Financial Liabilities, Net Amount	0	0
Other Counterparties
Derivative [Line Items]
Financial Assets, Net Amount Recognized	7,671	776
Financial Assets, Financial Instruments	-3,920	-5
Financial Assets, Collateral	0	0
Financial Assets, Net Amount	3,751	771
Financial Liabilities, Net Amount Recognized	14,300	60
Financial Liabilities, Financial Instruments	-3,920	-5
Financial Liabilities, Collateral	-8,663	0
Financial Liabilities, Net Amount	$1,717	$55

Operating_Segments_Details

Operating Segments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
	segment
Segment Reporting Information [Line Items]
Number of reportable segments	3
Net interest income	$350,823,000		$272,336,000		$292,788,000
Provision for credit losses	12,052,000		-5,804,000		-8,900,000
Non-interest income	221,305,000		154,394,000		129,193,000
Non-interest expense	436,782,000	[1]	294,588,000	[1]	304,030,000
Income tax expense	37,193,000		39,491,000		36,477,000
Net income	86,101,000		98,455,000		90,374,000
Total assets	14,602,099,000		9,641,427,000		9,571,805,000
Banking
Segment Reporting Information [Line Items]
Net interest income	328,326,000		267,131,000		290,881,000
Provision for credit losses	12,022,000		-6,167,000		-9,035,000
Non-interest income	115,411,000		92,936,000		93,124,000
Non-interest expense	350,358,000	[1]	259,753,000	[1]	284,452,000
Income tax expense	21,106,000		28,201,000		30,780,000
Net income	60,251,000		78,280,000		77,808,000
Total assets	12,698,740,000		9,167,127,000		9,187,480,000
Leasing
Segment Reporting Information [Line Items]
Net interest income	12,783,000		5,205,000		1,907,000
Provision for credit losses	35,000		363,000		135,000
Non-interest income	59,806,000		59,794,000		33,744,000
Non-interest expense	39,525,000	[1]	34,835,000	[1]	19,578,000
Income tax expense	12,524,000		11,290,000		5,697,000
Net income	20,505,000		18,511,000		10,241,000
Total assets	930,748,000		474,300,000		384,325,000
Mortgage Banking
Segment Reporting Information [Line Items]
Net interest income	9,714,000		0		0
Provision for credit losses	-5,000		0		0
Non-interest income	46,088,000		1,664,000		2,325,000
Non-interest expense	46,899,000	[1]	0	[1]	0
Income tax expense	3,563,000		0		0
Net income	5,345,000		1,664,000		2,325,000
Total assets	972,611,000		0		0
Taylor Capital Group, Inc.
Segment Reporting Information [Line Items]
Merger expenses, banking segment	$34,800,000		$2,500,000
[1]	Includes merger related expenses of $34.8 million and $2.5 million in the banking segment for the years ended December 31, 2014 and 2013, respectively.

Condensed_Parent_Company_Finan2

Condensed Parent Company Financial Information (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Assets
Cash	$312,081	$473,459	$287,543	$244,565
Other assets	297,690	197,416
Total assets	14,602,099	9,641,427	9,571,805
Liabilities and Stockholders’ Equity
Junior subordinated notes issued to capital trusts	185,778	152,065
Other liabilities	382,762	225,873
Stockholders’ equity	2,028,286	1,326,682	1,275,770	1,393,027
Total liabilities and stockholders’ equity	14,602,099	9,641,427
MB Financial, Inc.
Assets
Cash	32,161	122,001	57,303	108,323
Investments in subsidiaries	2,143,408	1,340,641
Other assets	38,941	24,505
Total assets	2,214,510	1,487,147
Liabilities and Stockholders’ Equity
Junior subordinated notes issued to capital trusts	185,778	152,065
Other liabilities	446	8,400
Stockholders’ equity	2,028,286	1,326,682
Total liabilities and stockholders’ equity	$2,214,510	$1,487,147

Condensed_Parent_Company_Finan3

Condensed Parent Company Financial Information (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Parent Company Financial Information
Income before income taxes	$123,294	$137,946	$126,851
Income tax benefit	37,193	39,491	36,477
Net income	86,101	98,455	90,374
Dividends and discount accretion on preferred shares	4,000		3,269
Net income available to common stockholders	82,101	98,455	87,105
MB Financial, Inc.
Condensed Parent Company Financial Information
Dividends from subsidiaries	101,500	80,500	146,000
Interest and other income	3,097	4,215	1,682
Interest and other expense	14,636	7,143	7,117
Income before income taxes	89,961	77,572	140,565
Income tax benefit	-4,590	-1,223	-2,192
Income before equity in undistributed net income of subsidiaries	94,551	78,795	142,757
Equity in undistributed net (loss) income of subsidiaries	-8,450	19,660	-52,383
Net income	86,101	98,455	90,374
Dividends and discount accretion on preferred shares	4,000	0	3,269
Net income available to common stockholders	$82,101	$98,455	$87,105

Condensed_Parent_Company_Finan4

Condensed Parent Company Financial Information (Details 3) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows From Operating Activities
Net income	$86,101	$98,455	$90,374
Adjustments to reconcile net income to net cash provided by operating activities:
Compensation expense for share-based payment plans	8,974	5,456	4,806
Cash Flows From Investing Activities
Net decrease in loans	155,399	38,725	219,125
Payments to Acquire Businesses, Net of Cash Acquired	-25,174	0	27,010
Net cash (used in) provided by investing activities	674,561	-39,247	330,163
Cash Flows From Financing Activities
Treasury stock transactions, net	-2,690	-1,672	-249
Stock options exercised	1,034	1,014	154
Excess tax benefits from share-based payment arrangements	396	-325	-390
Dividends paid on common stock	-34,210	-24,070	-7,101
Dividends paid on preferred stock	-2,000		-3,239
Net cash (used in) provided by financing activities	-1,003,386	32,405	-469,005
Net (decrease) increase in cash and cash equivalents	-161,378	185,916	42,978
Cash:
Beginning of year	473,459	287,543	244,565
End of year	312,081	473,459	287,543
MB Financial, Inc.
Cash Flows From Operating Activities
Net income	86,101	98,455	90,374
Adjustments to reconcile net income to net cash provided by operating activities:
Compensation expense for share-based payment plans	8,974	5,456	4,806
Equity in undistributed net income of subsidiaries	8,450	-19,660	52,383
Change in other assets and other liabilities	-8,980	-1,460	-5,064
Net cash provided by operating activities	94,545	82,791	142,499
Cash Flows From Investing Activities
Net decrease in loans	0	6,960	21,010
Payments to Acquire Businesses, Net of Cash Acquired	-101,546
Net cash (used in) provided by investing activities	-101,546	6,960	21,010
Cash Flows From Financing Activities
Treasury stock transactions, net	-2,690	-1,672	-249
Stock options exercised	1,034	1,014	154
Excess tax benefits from share-based payment arrangements	396	-325	-390
Dividends paid on common stock	-34,210	-24,070	-7,101
Dividends paid on preferred stock	-2,000	0	-3,239
Repurchase of preferred stock and warrant	0	0	-197,518
Redemption of on junior subordinated notes issued to capital trusts	-45,369	0	-6,186
Net cash (used in) provided by financing activities	-82,839	-25,053	-214,529
Net (decrease) increase in cash and cash equivalents	-89,840	64,698	-51,020
Cash:
Beginning of year	122,001	57,303	108,323
End of year	$32,161	$122,001	$57,303

Preferred_Stock_Details

Preferred Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Aug. 18, 2014	Dec. 31, 2013
Equity [Abstract]
Preferred stock, shares outstanding	4,000,000	4,000,000	0
Preferred stock, liquidation preference per share	$25		$0
Preferred stock, dividend rate	8.00%