Investment Securities - Amortized Cost and Fair Value of Debt Securities Available for Sale Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Schedule of Available-for-Sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 3,088
Due from one year to five years, Amortized Cost	41,430
Due from five to ten years, Amortized Cost	65,798
Due after ten years, Amortized Cost	25,270
Mortgage-backed securities, Amortized Cost	454,802	488,838	314,662
Due in one year or less, Estimated Fair Value	3,110
Due from one year to five years, Estimated Fair Value	43,038
Due from five to ten years, Estimated Fair Value	65,210
Due after ten years, Estimated Fair Value	24,744
Estimated Fair Value	456,713	486,235	324,029
Mortgage-Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Mortgage-backed securities, Amortized cost	319,216
Mortgage-backed securities, Amortized Cost	319,216	349,441	188,492
Mortgage-backed securities, Estimated Fair Value	320,611
Estimated Fair Value	$ 320,611	$ 347,750	$ 193,185