CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Comprehensive Income [Abstract]
Net income	$ 454,889	$ 361,775	$ 363,261
Foreign currency translation	(5,422)	2,375	(1,944)
Change in unrealized gain on marketable debt securities	(1,023)	(1,296)	(2,691)
Other	2,750	213	(171)
Total other comprehensive (loss) income	(3,695)	1,292	(4,806)
Comprehensive income	451,194	363,067	358,455
Comprehensive income (loss) attributable to noncontrolling interest	1,380	(1,025)	(1,232)
Comprehensive income attributable to common stockholders	$ 449,814	$ 364,092	$ 359,687