Borrowings - Summary of Bancorps Short Term Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
FHLB Advances
Short-term Debt [Line Items]
Maximum outstanding at any month end	$ 1,365,300	$ 1,383,000	$ 769,750
Average balance during the year	$ 844,835	$ 898,396	$ 120,309
Weighted-average interest rate during the year	0.60%	0.46%	0.55%
Federal Funds Purchased
Short-term Debt [Line Items]
Maximum outstanding at any month end	$ 85,000	$ 35,000	$ 125,000
Average balance during the year	$ 41,397	$ 13,312	$ 32,351
Weighted-average interest rate during the year	0.35%	0.31%	0.31%