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
Consolidated Statements of Comprehensive Income
Net income	$ 15,961	$ 61,826	$ 43,626	$ 76,902
Other comprehensive income (loss):
Unrealized net gain (loss) on marketable securities, net of tax	36	(422)	386	615
Other comprehensive income (loss):	36	(422)	386	615
Comprehensive income	$ 15,997	$ 61,404	$ 44,012	$ 77,517