Securities - Amortized Cost of Securities and their Estimated Fair Values (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
FHLB stock	$ 4,428	$ 4,428
FHLB stock	4,428	4,428
Amortized Cost	191,094	208,651
Gross Unrealized Gains	2,128	2,702
Gross Unrealized Losses	(935)	(1,873)
Estimated Fair Value	192,287	209,480
Estimated Fair Value, Less than 12 months	59,002	99,141
Unrealized Losses, Less than 12 months	(393)	(1,577)
Estimated Fair Value, 12 months or longer	26,498	10,898
Unrealized Losses, 12 months or longer	(542)	(296)
Estimated Fair Value	85,500	110,039
Unrealized Losses	(935)	(1,873)
U.S. Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	89,419	83,667
Gross Unrealized Gains	766	983
Gross Unrealized Losses	(356)	(638)
Estimated Fair Value	89,829	84,012
U.S. Agency Securities [Member] | Temporarily Impaired Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 months	31,029	41,963
Unrealized Losses, Less than 12 months	(212)	(597)
Estimated Fair Value, 12 months or longer	8,217	3,459
Unrealized Losses, 12 months or longer	(144)	(41)
Estimated Fair Value	39,246	45,422
Unrealized Losses	(356)	(638)
Taxable Municipals Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,281	2,720
Gross Unrealized Gains	10	17
Gross Unrealized Losses	(6)	(10)
Estimated Fair Value	1,285	2,727
Taxable Municipals Bonds [Member] | Temporarily Impaired Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 months	519	1,347
Unrealized Losses, Less than 12 months	(6)	(10)
Estimated Fair Value	519	1,347
Unrealized Losses	(6)	(10)
Tax Free Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,349	33,004
Gross Unrealized Gains	903	1,081
Gross Unrealized Losses	(21)	(174)
Estimated Fair Value	28,231	33,911
Tax Free Municipal Bonds [Member] | Temporarily Impaired Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 months	1,666	7,369
Unrealized Losses, Less than 12 months	(4)	(174)
Estimated Fair Value, 12 months or longer	928
Unrealized Losses, 12 months or longer	(17)
Estimated Fair Value	2,594	7,369
Unrealized Losses	(21)	(174)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	71,399	85,626
Gross Unrealized Gains	378	437
Gross Unrealized Losses	(552)	(1,051)
Estimated Fair Value	71,225	85,012
Mortgage-Backed Securities [Member] | Temporarily Impaired Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 months	25,788	48,462
Unrealized Losses, Less than 12 months	(171)	(796)
Estimated Fair Value, 12 months or longer	17,353	7,439
Unrealized Losses, 12 months or longer	(381)	(255)
Estimated Fair Value	43,141	55,901
Unrealized Losses	(552)	(1,051)
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,000
Gross Unrealized Gains		1
Estimated Fair Value		2,001
Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,646	1,634
Gross Unrealized Gains	71	183
Estimated Fair Value	$ 1,717	$ 1,817