Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 3,026
Due from one year to five years, Amortized Cost	37,087
Due from five to ten years, Amortized Cost	64,362
Due after ten years, Amortized Cost	30,805
Mortgage-backed securities, Amortized cost	177,196
Mortgage-backed securities, Amortized Cost	312,476	336,710	355,160
Due in one year or less, Fair Value	3,029
Due from one year to five years, Fair Value	38,668
Due from five to ten years, Fair Value	64,876
Due after ten years, Fair Value	30,611
Mortgage-backed securities, Fair Value	178,984
Fair Value	$ 316,168	$ 346,909	$ 366,980