Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other 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
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ 605,224	$ 321,673
Other comprehensive income (loss)	$ 39	$ 48	(200)	136
Ending Balance	640,366	589,333	640,366	589,333
Unrealized Net Gains and (Losses) on Securities Available-for-Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(612)	(224)
Other comprehensive income (loss), before reclassifications			(192)	134
Amounts reclassified from accumulated other comprehensive income (loss), net of tax of ($61) (1)			178
Other comprehensive income (loss)			(14)	134
Ending Balance	(626)	(90)	(626)	(90)
Other comprehensive income (loss), before reclassifications, tax			77	(83)
Reclassification from AOCI, tax			(61)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			12	0
Other comprehensive income (loss), before reclassifications			(8)	2
Amounts reclassified from accumulated other comprehensive income (loss), net of tax of ($61) (1)			0
Other comprehensive income (loss)			(8)	2
Ending Balance	$ 4	$ 2	4	$ 2
Other comprehensive income (loss), before reclassifications, tax			$ 2