Investment Securities - Fair Value and Gross Unrealized Losses (Detail) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Available for sale:
Fair Value, Unrealized Loss Position, Less than 12 months		$ 57,062	$ 81,135
Fair Value, Unrealized Loss Position, 12 months or More		81,917	106,433
Total Fair Value		138,979	187,568
Available for sale:
Unrealized Loss, Unrealized Loss Position, Less than 12 months		(284)	(339)
Unrealized Loss, Unrealized Loss Position, 12 months or More		(1,277)	(2,903)
Total Unrealized Loss		(1,561)	(3,242)
GNMA mortgage-backed securities
Available for sale:
Fair Value, Unrealized Loss Position, Less than 12 months		0	27,113
Fair Value, Unrealized Loss Position, 12 months or More		68,286	98,230
Total Fair Value		68,286	125,343
Available for sale:
Unrealized Loss, Unrealized Loss Position, Less than 12 months		0	(110)
Unrealized Loss, Unrealized Loss Position, 12 months or More		(1,120)	(2,683)
Total Unrealized Loss		(1,120)	(2,793)
Other securities
Available for sale:
Fair Value, Unrealized Loss Position, Less than 12 months		0	2
Fair Value, Unrealized Loss Position, 12 months or More		24	25
Total Fair Value		24	27
Available for sale:
Unrealized Loss, Unrealized Loss Position, Less than 12 months		0	(1)
Unrealized Loss, Unrealized Loss Position, 12 months or More		(30)	(31)
Total Unrealized Loss		(30)	(32)
Corporate bonds
Held to maturity:
Fair Value, Unrealized Loss Position, Less than 12 Months		15,477
Fair Value, Unrealized Loss Position, 12 Months or More		0
Total Fair Value		15,477
Held to maturity:
Unrealized Loss, Unrealized Loss Position, Less than 12 Months		(15)
Unrealized Loss, Unrealized Loss Position, 12 Months or More		0
Total Unrealized Loss		(15)
Government sponsored agency mortgage-backed securities
Available for sale:
Fair Value, Unrealized Loss Position, Less than 12 months	[1]	57,062	54,020
Fair Value, Unrealized Loss Position, 12 months or More	[1]	13,607	8,178
Total Fair Value	[1]	70,669	62,198
Available for sale:
Unrealized Loss, Unrealized Loss Position, Less than 12 months	[1]	(284)	(228)
Unrealized Loss, Unrealized Loss Position, 12 months or More	[1]	(127)	(189)
Total Unrealized Loss	[1]	$ (411)	$ (417)

[1] Includes mortgage-backed securities and CMOs.