Other Comprehensive Income (Loss) - Summary of Reclassification Out of Each Component of Accumulated Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net gains on securities available for sale	$ 94	$ 301	$ 233	$ 330
Tax expense	(2,214)	(3,377)	(4,003)	(3,934)
Net income	9,541	8,189	18,097	9,727
Amount Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net income	(74)	(196)	(184)	(215)
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	(94)	(301)	(233)	(330)
Tax expense	$ 20	$ 105	$ 49	$ 115