Investment Securities - Scheduled Maturities of Investment Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Investments Debt And Equity Securities [Abstract]
Available-for-Sale, Maturing within one year, Amortized Cost	$ 183
Available-for-Sale, Maturing after one to five years, Amortized Cost	8,430
Available-for-Sale, Maturing after five to ten years, Amortized Cost	118,477
Available-for-Sale, Maturing after ten years, Amortized Cost	73,609
Available-for-Sale, Amortized Cost	200,699	$ 202,039
Available-for-Sale, Maturing within one year, Estimated Fair Value	185
Available-for-Sale, Maturing after one to five years, Estimated Fair Value	8,771
Available-for-Sale, Maturing after five to ten years, Estimated Fair Value	118,776
Available-for-Sale, Maturing after ten years, Estimated Fair Value	74,515
Available-for-Sale, Estimated Fair Value, Total	202,247	204,966
Held-to-Maturity, Maturing within one year, Amortized Cost	968
Held-to-Maturity, Maturing after one to five years, Amortized Cost	9,059
Held-to-Maturity, Maturing after five to ten years, Amortized Cost	33,902
Held-to-Maturity, Amortized Cost	43,929	29,120
Held-to-Maturity, Maturing within one year, Estimated Fair Value	956
Held-to-Maturity, Maturing after one to five years, Estimated Fair Value	9,038
Held-to-Maturity, Maturing after five to ten years, Estimated Fair Value	33,635
Held-to-Maturity, Estimated Fair Value, Total	$ 43,629	$ 29,154