Borrowings - Summary of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Securities sold under repurchase agreements	$ 279,730	$ 266,732
Federal Home Loan Bank advances	1,075,000	1,090,000
Federal funds purchased	782,000	568,000
Subordinated notes	123,681	124,164
Total short-term borrowings	$ 2,260,411	$ 2,048,896