CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 113,098	$ 90,092	$ 361,775
Other comprehensive income (loss):
Foreign currency translation	(2,091)	1,949
Change in unrealized gain on marketable debt securities	61	(308)
Other	504	223
Total other comprehensive (loss) income	(1,526)	1,864	1,292
Comprehensive income	111,572	91,956
Comprehensive income (loss) attributable to noncontrolling interest	905	(534)
Comprehensive income attributable to common stockholders	$ 110,667	$ 92,490