Borrowed Funds - Schedule of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total short-term borrowings	$ 1,080,960	$ 1,076,991
Short-term borrowings
Debt Instrument [Line Items]
Securities sold under agreements to repurchase	298,960	500,991
Federal funds purchased	0	50,000
FHLB advances	782,000	526,000
Total short-term borrowings	$ 1,080,960	$ 1,076,991