Business Combinations (Narrative) (Details) $ in Thousands												12 Months Ended	84 Months Ended
	Nov. 18, 2016 USD ($) locations	Aug. 19, 2016	Mar. 31, 2016 USD ($) locations	Jul. 24, 2015 USD ($) locations	Jul. 17, 2015 USD ($) locations	Jul. 02, 2015 USD ($)	Jan. 16, 2015 USD ($) locations	Aug. 08, 2014 USD ($) locations	Jul. 11, 2014 USD ($)	May 16, 2014 USD ($)	Apr. 28, 2014 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 locations	Jul. 01, 2015 USD ($) locations
Business Acquisition [Line Items]
Number of locations | locations	2		1
Additional goodwill recorded on acquisition												$ 24,652
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets												80.00%
First Community Financial Corporation
Business Acquisition [Line Items]
Date of acquisition	Nov. 18, 2016
Fair value of assets acquired, at the acquisition date	$ 187,200
Fair value of loans acquired, at the acquisition date	79,200
Fair value of deposits	150,300
Additional goodwill recorded on acquisition	13,100
GE Capital Franchise Finance
Business Acquisition [Line Items]
Date of acquisition		Aug. 19, 2016
Fair value of loans acquired, at the acquisition date	$ 561,400
Generations Bancorp Inc
Business Acquisition [Line Items]
Date of acquisition			Mar. 31, 2016
Fair value of assets acquired, at the acquisition date			$ 134,200
Fair value of loans acquired, at the acquisition date			67,400
Fair value of deposits			100,200
Additional goodwill recorded on acquisition			$ 11,500
Community Financial Shares Inc.
Business Acquisition [Line Items]
Date of acquisition				Jul. 24, 2015
Number of locations | locations				4
Fair value of assets acquired, at the acquisition date				$ 350,500
Fair value of loans acquired, at the acquisition date				159,500
Fair value of deposits				290,000
Additional goodwill recorded on acquisition				$ 27,600
Suburban Illinois Bancorp
Business Acquisition [Line Items]
Date of acquisition					Jul. 17, 2015
Number of locations | locations					10
Fair value of assets acquired, at the acquisition date					$ 494,700
Fair value of loans acquired, at the acquisition date					257,800
Fair value of deposits					416,700
Additional goodwill recorded on acquisition					$ 18,600
North Bank
Business Acquisition [Line Items]
Date of acquisition						Jul. 01, 2015
Number of locations | locations														2
Fair value of assets acquired, at the acquisition date														$ 117,900
Fair value of loans acquired, at the acquisition date														51,600
Fair value of deposits														$ 101,000
Additional goodwill recorded on acquisition						$ 6,700
Delavan Bancshares
Business Acquisition [Line Items]
Date of acquisition							Jan. 16, 2015
Number of locations | locations							4
Fair value of assets acquired, at the acquisition date							$ 224,100
Fair value of loans acquired, at the acquisition date							128,000
Fair value of deposits							170,200
Fair value of liabilities assumed, at the acquisition date							186,400
Additional goodwill recorded on acquisition							$ 16,800
THE National Bank
Business Acquisition [Line Items]
Date of acquisition									Jul. 11, 2014
Fair value of assets acquired, at the acquisition date									$ 94,100
Fair value of loans acquired, at the acquisition date									75,000
Fair value of deposits									36,200
Additional goodwill recorded on acquisition									$ 16,300
Urban Partnership Bank, Stone Park Branch
Business Acquisition [Line Items]
Date of acquisition										May 16, 2014
Fair value of deposits										$ 5,400
Fair value of liabilities assumed, at the acquisition date										5,500
Additional goodwill recorded on acquisition										$ 678
FDIC Assisted
Business Acquisition [Line Items]
Number of FDIC-assisted banks acquired | locations													9
Policy Billing Services Inc. And Equity Premium Finance Inc.
Business Acquisition [Line Items]
Date of acquisition											Apr. 28, 2014
Fair value of loans acquired, at the acquisition date											$ 7,400
Additional goodwill recorded on acquisition											$ 6,500
Number of FDIC-assisted banks acquired											2
Community Banking
Business Acquisition [Line Items]
Additional goodwill recorded on acquisition												$ 24,652
Community Banking | Talmer Bank & Trust
Business Acquisition [Line Items]
Date of acquisition								Aug. 08, 2014
Number of locations | locations								11
Fair value of assets acquired, at the acquisition date								$ 361,300
Fair value of loans acquired, at the acquisition date								41,500
Fair value of deposits								354,900
Fair value of liabilities assumed, at the acquisition date								361,300
Additional goodwill recorded on acquisition								$ 9,700
Wealth Management
Business Acquisition [Line Items]
Additional goodwill recorded on acquisition												$ 0
Wealth Management | Talmer Bank & Trust
Business Acquisition [Line Items]
Date of acquisition								Aug. 08, 2014
Additional goodwill recorded on acquisition								$ 250