Borrowed Funds - Summary of Borrowed Funds by Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Balance at End of Period	$ 710,001	$ 854,236
Weighted Average Interest Rate	1.51%	0.78%
Maximum Outstanding at Month End During the Period	$ 924,518	$ 886,767
Average Amount Outstanding During the Year	$ 716,962	$ 735,975
Weighted Average Interest Rate During the Year	1.15%	0.67%
Federal funds purchased and securities sold under agreements to repurchase
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Balance at End of Period	$ 28,000	$ 130,000
Weighted Average Interest Rate	1.54%	0.79%
Maximum Outstanding at Month End During the Period	$ 135,000	$ 130,000
Average Amount Outstanding During the Year	$ 87,438	$ 112,150
Weighted Average Interest Rate During the Year	1.11%	0.54%
Trust preferred borrowings
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Balance at End of Period	$ 67,011	$ 67,011
Weighted Average Interest Rate	3.25%	2.66%
Maximum Outstanding at Month End During the Period	$ 67,011	$ 67,011
Average Amount Outstanding During the Year	$ 67,011	$ 67,011
Weighted Average Interest Rate During the Year	2.89%	2.42%
Senior Debt
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Balance at End of Period	$ 98,171	$ 155,000
Weighted Average Interest Rate	5.12%	5.12%
Maximum Outstanding at Month End During the Period	$ 155,000	$ 155,000
Average Amount Outstanding During the Year	$ 134,136	$ 110,191
Weighted Average Interest Rate During the Year	4.38%	3.82%
Other borrowed funds
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Balance at End of Period	$ 34,623	$ 64,150
Weighted Average Interest Rate	0.09%	0.09%
Maximum Outstanding at Month End During the Period	$ 97,984	$ 64,150
Average Amount Outstanding During the Year	$ 43,514	$ 21,335
Weighted Average Interest Rate During the Year	0.09%	0.09%