CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 118,599	$ 111,821	$ 346,230	$ 275,649	$ 361,775
Other comprehensive income (loss):
Foreign currency translation	1,665	2,838	(3,148)	3,180
Change in unrealized gain on marketable debt securities	(208)	(509)	(1,015)	(1,220)
Other	84	(107)	2,102	(396)
Total other comprehensive income (loss)	1,541	2,222	(2,061)	1,564	1,292
Comprehensive income	120,140	114,043	344,169	277,213
Comprehensive income (loss) attributable to noncontrolling interest	303	(61)	1,161	(884)
Comprehensive income attributable to common stockholders	$ 119,837	$ 114,104	$ 343,008	$ 278,097