Borrowings (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 19, 2003
Debt Instrument [Line Items]
Repurchase agreements	$ 51,052,000	$ 17,000,000
Federal funds purchased	0
Remaining lines of credit available with FHLB	$ 254,000,000
Trust preferred securities, issued			$ 5,000,000
Pooled underwriting			$ 344,000,000
Weighted average interest rate, trust preferred securities	4.09%
Junior subordinated debt securities	$ 1,978,909,000	$ 1,049,698,000
Maximum inclusion percentage, Tier 1 Capital			25.00%
Short-term Debt [Member]
Debt Instrument [Line Items]
Federal funds purchased	62,500,000
Senior Unsecured Note [Member]
Debt Instrument [Line Items]
FHLB advances, collateral pledged	$ 492,200,000
Minimum [Member]
Debt Instrument [Line Items]
Interest rate, trust preferred securities	3.89%
Maximum [Member]
Debt Instrument [Line Items]
Interest rate, trust preferred securities	4.23%
Subsidiaries [Member]
Debt Instrument [Line Items]
Junior subordinated debt securities	$ 5,200,000