Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 2,214
Due from one year to five years, Amortized Cost	36,699
Due from five to ten years, Amortized Cost	68,790
Due after ten years, Amortized Cost	30,199
Mortgage-backed securities, Amortized cost	176,818
Mortgage-backed securities, Amortized Cost	314,720	336,710	349,581
Due in one year or less, Fair Value	2,229
Due from one year to five years, Fair Value	37,826
Due from five to ten years, Fair Value	67,622
Due after ten years, Fair Value	28,917
Mortgage-backed securities, Fair Value	175,654
Fair Value	$ 312,248	$ 346,909	$ 361,051