Business Segment Information - Net Interest Income and Noninterest Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 8,480	$ 8,489	$ 17,183	$ 16,638
Noninterest income	864	616	1,618	1,498
Assets	1,100,915		1,100,915		$ 1,062,389
Commercial
Segment Reporting Information [Line Items]
Net interest income	8,623	8,562	17,465	16,805
Noninterest income	859	613	1,600	1,492
Assets	1,084,682		1,084,682		1,051,501
Other
Segment Reporting Information [Line Items]
Net interest income	(143)	(73)	(282)	(167)
Noninterest income	5	$ 3	18	$ 6
Assets	$ 16,233		$ 16,233		$ 10,888