Investment Securities - Fair Value and Gross Unrealized Losses, Available for Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Mortgage backed securities
Available-for-sale:
Fair Value, Unrealized Loss Position Less than 12 months	$ 223,464	$ 81,135
Unrealized Loss, Unrealized Loss Position Less than 12 months	(2,138)	(339)
Fair Value, Unrealized Loss Position 12 months or More	74,678	106,433
Unrealized Loss, Unrealized Loss Position 12 months or More	(2,039)	(2,903)
Total Fair Value	298,142	187,568
Total Unrealized Loss	(4,177)	$ (3,242)
Corporate bonds
Held-to-Maturity:
Fair Value, Unrealized Loss Position Less than 12 months	15,422
Unrealized Loss, Unrealized Loss Position Less than 12 months	(70)
Fair Value, Unrealized Loss Position 12 months or More	0
Unrealized Loss, Unrealized Loss Position 12 months or More	0
Total Fair Value	15,422
Total Unrealized Loss	$ (70)