Other Comprehensive Income (Loss) - Summary of Reclassification Out of Each Component of Accumulated Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net gains on securities available for sale	$ 128						$ 420	$ 233
Tax expense	(2,383)			$ (2,217)			(6,553)	(6,220)
Net income	10,504	$ 10,486	$ 8,656	$ 9,529	$ 9,541	$ 8,556	29,646	27,626
Amount Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net income	(101)						(332)	(184)
Amount Reclassified From Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net gains on securities available for sale	(128)						(420)	(233)
Tax expense	$ 27						$ 88	$ 49