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 ($) office shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition
Credit facility drawn					$ 372,882	$ 597,847
Merger expenses					8,522	61,134	$ 7,804
Goodwill					1,134,568	1,133,534
Line of Credit
Business Acquisition
Credit facility drawn	$ 125,000				19,963	124,625
Repayments of lines of credit	25,000
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				$ (1,000)
Cash paid	107,638
Total assets acquired	764,748
Goodwill	847,701
Intangibles acquired	$ 19,088
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
Service provided by acquiree bank through number of branches (in office) | office		5
Share price (in dollars per share) | $ / shares		$ 16.64
Stock consideration given		$ 132,900
Cash paid		54,478
Total assets acquired		1,240,000
Loans		985,500				985,542
Total deposits acquired		924,700				924,697
Goodwill		101,061				101,061
Core deposits and other intangible assets acquired		$ 8,600
Acquisition related expenses							5,500
Intangibles acquired						8,003
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
Service provided by acquiree bank through number of branches (in office) | office			5
Cash paid			$ 203
Total assets acquired			182,800
Loans							121,783
Total deposits acquired			144,300				144,300
Goodwill			$ 5,339				5,339
Acquisition related expenses							2,300
Intangibles acquired							$ 1,930
Outstanding contractual principal balance of acquired loan portfolio					76,000	92,400
Carrying amount of acquired loan portfolio					$ 70,800	$ 86,400