Investment Securities - Contractual Maturities of Investment Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Due in one year or less, Amortized Cost	$ 3,513	$ 2,635
Due after one year through five years, Amortized Cost	248	248
Due after five years through ten years, Amortized Cost	31,474	37,471
Due after ten years, Amortized Cost	13,024	13,024
Total investment securities, excluding mortgage-backed securities, Amortized Cost	48,259	53,378
Total investment securities, Amortized Cost	303,154	300,028
Due in one year or less, Estimated Fair Value	3,510	2,635
Due after one year through five years, Estimated Fair Value	248	248
Due after five years through ten years, Estimated Fair Value	31,466	37,319
Due after ten years, Estimated Fair Value	11,420	10,826
Total investment securities, excluding mortgage-backed securities, Estimated Fair Value	46,644	51,028
Total investment securities, Estimated Fair Value	299,502	295,686
Due in one year or less, Amortized Cost	250	250
Total investment securities, excluding mortgage-backed securities, Amortized Cost	250	250
Total investment securities, Amortized Cost	250	250
Due in one year or less, Estimated Fair Value	250	250
Total investment securities, excluding mortgage-backed securities, Estimated Fair Value	250	250
Total investment securities, Estimated Fair Value	250	250
U.S. Government Agency Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total investment securities, Amortized Cost	254,895	246,650
Total investment securities, Estimated Fair Value	$ 252,858	$ 244,658