Comprehensive Income - Components of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Before Tax Amount
Other comprehensive loss, net	$ (7,144)	$ (1,334)
Tax Benefit (Expense)
Other comprehensive loss, net	1,695	433
Net of Tax Amount
Other comprehensive loss	(5,449)	(901)
Net unrealized gains (losses) on available for sale securities
Before Tax Amount
Net unrealized holding losses arising during period	(7,502)	1,184
Reclassification adjustment for net gains arising during the period	0	(2,539)
Other comprehensive loss, net	(7,502)	(1,355)
Tax Benefit (Expense)
Net unrealized holding losses arising during period	1,770	(450)
Reclassification adjustment for net gains arising during the period	0	890
Other comprehensive loss, net	1,770	440
Net of Tax Amount
Net unrealized holding losses arising during period	(5,732)	734
Reclassification adjustment for net gains arising during the period	0	(1,649)
Other comprehensive loss	(5,732)	(915)
Unrealized gains on derivatives
Before Tax Amount
Other comprehensive loss, net	358	21
Tax Benefit (Expense)
Other comprehensive loss, net	(75)	(7)
Net of Tax Amount
Other comprehensive loss	$ 283	$ 14