Borrowings - Short Term Borrowings (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Abstract]
FHLB advances, amount	$ 1,365,300	$ 1,298,000
Federal funds purchased, carrying value	70,000	0
Total short-term borrowings, amount	$ 1,435,300	$ 1,298,000
FHLB advances, rate	0.48%	0.29%
Federal funds purchased, rate	0.56%	0.00%