Mergers and Acquisitions (Textual) (Details) $ / shares in Units, $ in Thousands					3 Months Ended		12 Months Ended
	Aug. 31, 2016 USD ($) $ / shares shares	May 31, 2015 USD ($) office $ / shares shares	Apr. 01, 2015 USD ($) office shares	Oct. 31, 2014 USD ($) office	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition
Credit facility drawn					$ 597,847		$ 597,847	$ 242,391
Merger and acquisition-related transaction expenses							61,134	7,804	$ 6,388
Goodwill					1,133,534		1,133,534	287,393
Talmer
Business Acquisition
Acquisition purchase price	$ 1,612,449
Stock consideration given (in shares) | shares	32,100,000
Exchange ratio of common stock issued	0.4725
Share price (in dollars per share) | $ / shares	$ 1.61
Repayments of lines of credit	$ 37,500
Decrease in goodwill recognized					3,600
Total assets acquired	765,782
Cash paid	107,638
Goodwill	846,667
Goodwill acquired during period							846,700
Contractual cash flows not expected to be collected (nonaccretable difference)	223,959
Outstanding contractual principal balance of acquired loan portfolio					4,500,000		4,500,000
Carrying amount of acquired loan portfolio					4,400,000		4,400,000
Intangibles acquired	19,088
Talmer | Other intangibles
Business Acquisition
Increase (decrease) in intangible assets					6,700
Talmer | Core deposit intangible assets
Business Acquisition
Increase (decrease) in intangible assets					(2,500)
Lake Michigan
Business Acquisition
Acquisition purchase price		$ 187,394						187,394
Stock consideration given (in shares) | shares		4,300,000
Exchange ratio of common stock issued		1.326
Share price (in dollars per share) | $ / shares		$ 16.64
Total assets acquired		$ 1,240,000
Loans		985,500						985,542
Total deposits acquired		$ 924,700						924,697
Service provided by acquiree bank through number of branches (in office) | office		5
Stock consideration given		$ 132,900
Cash paid		54,478
Goodwill		101,061						101,061
Core deposits and other intangible assets acquired		8,600
Goodwill acquired during period						$ 600
Contractual cash flows not expected to be collected (nonaccretable difference)		22,600
Outstanding contractual principal balance of acquired loan portfolio					656,100		656,100	864,400
Carrying amount of acquired loan portfolio					634,200		634,200	841,800
Purchase accounting fair value adjustment, core deposit intangibles		$ (8,003)
Intangibles acquired								8,003
Acquisition related expenses							5,500
Monarch
Business Acquisition
Acquisition purchase price			$ 27,191					27,191
Stock consideration given (in shares) | shares			860,575
Exchange ratio of common stock issued			0.0982
Total assets acquired			$ 182,800
Loans								121,783
Total deposits acquired			$ 144,300					144,300
Service provided by acquiree bank through number of branches (in office) | office			5
Cash paid			$ 203
Goodwill			5,339					5,339
Contractual cash flows not expected to be collected (nonaccretable difference)			7,100
Outstanding contractual principal balance of acquired loan portfolio					92,400		92,400	114,900
Carrying amount of acquired loan portfolio					86,400		86,400	108,300
Purchase accounting fair value adjustment, core deposit intangibles			$ (1,930)
Intangibles acquired								1,930
Acquisition related expenses							2,300
Northwestern Bancorp
Business Acquisition
Acquisition purchase price				$ 121,000
Total assets acquired				815,000
Loans				475,300
Total deposits acquired				$ 794,400
Service provided by acquiree bank through number of branches (in office) | office				25
Goodwill									60,300
Contractual cash flows not expected to be collected (nonaccretable difference)				$ 33,500
Outstanding contractual principal balance of acquired loan portfolio					283,100		283,100	361,300
Carrying amount of acquired loan portfolio					254,100		254,100	329,900
Intangibles acquired				$ 12,900
Acquisition related expenses									$ 5,800
Line of Credit
Business Acquisition
Credit facility drawn	125,000				$ 124,625		$ 124,625	$ 25,000
Repayments of lines of credit	$ 25,000