Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax effect	$ 2,705	$ 1,914
Total accumulated other comprehensive loss	(10,178)	(3,551)
Unrealized Gain (Loss) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before tax	(12,062)	(3,937)
Unamortized Gain on Securities Held to Maturity, Previously Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before tax	148	200
Unrealized Loss on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before tax	$ (969)	$ (1,728)