Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 40,440	$ 19,224	$ 15,865
Change in net unrealized loss on investments, net of tax	(462)	(57)	(202)
Less: reclassification adjustment for net realized gain (loss) included in net income, net of tax	44	112	(19)
Net change	418	(55)	221
Comprehensive income	$ 40,022	$ 19,279	$ 15,644