Borrowings (Additional Information) (Details) - USD ($)	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
FHLB advances		$ 7,360,000,000
Additional borrowing availability through the FHLB		193,500,000
Debt Instrument [Line Items]
Long-term borrowings, Amount		372,882,000	$ 597,847,000
Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 145,000,000
Long-term borrowings, Amount	125,000,000	$ 19,963,000	$ 124,625,000
Repayment of debt	25,000,000
Line of Credit | Term Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	125,000,000
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	20,000,000
Line of Credit Acquired in Merger With Talmer | Line of Credit
Debt Instrument [Line Items]
Repayment of debt	$ 37,500,000