Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 79,510	$ 77,993	$ 102,218	$ 112,247
Other comprehensive income:
Change in unrealized gain (loss) on available-for-sale securities	24		(10)
Amounts reclassified into earnings related to investments	10		10
Other comprehensive income, net	34
Comprehensive income	$ 79,544	$ 77,993	$ 102,218	$ 112,247