Short-term Borrowings - Summary of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Ending Balance	$ 867,943	$ 1,510,825	$ 1,105,876
Average Balance	$ 1,387,737	$ 1,252,531	$ 815,393
Average Rate	0.58%	0.40%	0.30%
Federal funds purchased
Short-term Debt [Line Items]
Ending Balance	$ 0	$ 4,000	$ 9,000
Average Balance	$ 6,887	$ 14,832	$ 11,691
Average Rate	0.60%	0.36%	0.36%
Borrowings from FHLB
Short-term Debt [Line Items]
Ending Balance	$ 748,000	$ 1,400,000	$ 945,000
Average Balance	$ 1,265,932	$ 1,117,522	$ 644,651
Average Rate	0.61%	0.42%	0.31%
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Ending Balance	$ 119,943	$ 106,825	$ 151,876
Average Balance	$ 114,918	$ 120,177	$ 159,051
Average Rate	0.23%	0.23%	0.24%
Maximum [Member]
Short-term Debt [Line Items]
Ending Balance	$ 1,530,678	$ 1,510,825	$ 1,105,876
Weighted Average [Member]
Short-term Debt [Line Items]
Average Rate	0.63%	0.53%	0.30%