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	$ 84,402	$ 65,991	$ 39,390
Other comprehensive income:
Unrealized loss on available-for-sale securities, net of tax	(2)	(3)	(3)
Comprehensive income	$ 84,400	$ 65,988	$ 39,387