Securities - Fair Value and Amortized Cost of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Available-for-Sale, Amortized Cost, One to five years	$ 499
Available-for-Sale, Amortized Cost, Five to ten years	7,766
Available-for-Sale, Amortized Cost, After ten years	210
Available-for-Sale, Amortized Cost, Mortgage-backed securities	88,257
Available-for-Sale, Amortized Cost, Total debt securities	96,732
Available-for-Sale, Fair Value, One to five years	499
Available-for-Sale, Fair Value, Five to ten years	7,821
Available-for-Sale, Fair Value, After ten years	223
Available-for-Sale, Fair Value, Mortgage-backed securities	86,703
Available-for-Sale, Fair Value, Total debt securities	95,246
Held-to-Maturity, Amortized Cost, Within one year	2,812
Held-to-Maturity, Amortized Cost, One to five years	21,423
Held-to-Maturity, Amortized Cost, Five to ten years	30,942
Held-to-Maturity, Amortized Cost, After ten years	71,783
Held-to-Maturity, Amortized Cost, Mortgage-backed securities	338,749
Held-to-Maturity, Amortized Cost	465,709	$ 310,539
Held-to-Maturity, Fair Value, Within one year	3,006
Held-to-Maturity, Fair Value, One to five years	21,785
Held-to-Maturity, Fair Value, Five to ten years	31,495
Held-to-Maturity, Fair Value, After ten years	70,137
Held-to-Maturity, Fair Value, Mortgage-backed securities	334,733
Held-to-Maturity, Fair Value, Total debt securities	$ 461,156	$ 312,802