Investment Securities - Amortized Cost and Fair Value of Debt Securities Available for Sale Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Schedule of Available-for-Sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 5,055
Due from one year to five years, Amortized Cost	41,290
Due from five to ten years, Amortized Cost	66,456
Due after ten years, Amortized Cost	56,461
Total amortized cost	530,456	488,838	312,476
Due in one year or less, Estimated Fair Value	5,123
Due from one year to five years, Estimated Fair Value	42,911
Due from five to ten years, Estimated Fair Value	66,794
Due after ten years, Estimated Fair Value	56,355
Mortgage-backed securities, Amortized Cost	535,630	486,235	316,168
Mortgage-Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Mortgage-backed securities, Amortized cost	361,194
Total amortized cost	361,194	349,441	177,196
Mortgage-backed securities, Estimated Fair Value	364,447
Mortgage-backed securities, Amortized Cost	$ 364,447	$ 347,750	$ 178,984