Securities - Maturity of Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Held for Investment, Contractual maturity of debt securities, Amortized Cost
Amortized cost, Within one year	$ 1,563	$ 1,561
Amortized cost, After one year but within five years	1,751	1,937
Amortized cost, After five years but within ten years	673	707
Amortized cost, After ten years	16	160
Amortized Cost	4,003	4,365
Available for sale, Contractual maturity of debt securities, Amortized Cost
Amortized Cost, Within one year	75,206	66,542
Amortized Cost, After one year but within five years	308,182	320,150
Amortized Cost, After five years but within ten years	6,318	5,830
Amortized Cost, After ten years	62,933	66,199
Total debt securities	452,639	458,721
Amortized Cost, Equity securities	6,746	6,594
Amortized Cost	459,385	465,315
Held for Investment, Contractual maturity of debt securities, Estimated Fair Value
Estimated Fair Value, Within one year	1,573	1,568
Estimated Fair Value, After one year but within five years	1,762	1,951
Estimated Fair Value, After five years but within ten years	687	723
Estimated Fair Value, After ten years	16	161
Estimated Fair Value	4,038	4,403
Available for sale, Contractual maturity of debt securities, Estimated Fair Value
Estimated Fair Value, Within one year	75,378	66,662
Estimated Fair Value, After one year but within five years	308,229	319,839
Estimated Fair Value, After five years but within ten years	6,666	6,152
Estimated Fair Value, After ten years	62,929	66,246
Total debt securities	453,202	458,899
Estimated Fair Value, Equity securities	6,045	6,569
Estimated Fair Value, Total	$ 459,247	$ 465,468