Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 8,452	$ 4,996	$ 37,584	$ 13,317
Change in foreign currency translation loss, net of zero tax	0	0	0	0
Available-for-sale investments:
Change in net unrealized gain (loss) on investments, net of tax	103	(58)	32	140
Less: reclassification adjustment for net realized gain included in net income	12	(38)	4	87
Net change, net of tax	115	(96)	36	227
Other comprehensive income (loss), net	115	(96)	36	227
Comprehensive income	$ 8,567	$ 4,900	$ 37,620	$ 13,544