CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 419,222	$ 477,001	$ 454,669
Other comprehensive loss:
Foreign currency translation	(14,792)	(17,153)	(5,422)
Change in unrealized gain on marketable debt securities	(5,047)	7,001	(1,023)
Other	(847)	3,614	2,750
Total other comprehensive loss	(20,686)	(6,538)	(3,695)
Comprehensive income	398,536	470,463	450,974
Comprehensive income attributable to noncontrolling interest	1,379	1,234	1,160
Comprehensive income attributable to common stockholders	$ 397,157	$ 469,229	$ 449,814