CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net income	$ 361,775	$ 363,261	$ 249,729
Foreign currency translation	2,375	(1,944)	6,951
Change in unrealized gain on marketable debt securities	(1,296)	(2,691)	354
Other	213	(171)	(106)
Total other comprehensive income (loss)	1,292	(4,806)	7,199
Comprehensive income	363,067	358,455	256,928
Comprehensive (loss) income attributable to noncontrolling interest	(1,025)	(1,232)	3,562
Comprehensive income attributable to common stockholders	$ 364,092	$ 359,687	$ 253,366