Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net Income	$ 36,995	$ 21,302	$ 78,554	$ 50,270
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment, net of tax of $56 and $(23) for the three months ended September 30, 2014 and 2013, respectively and $49 and $(12) for the nine months ended September 30, 2014 and 2013, respectively	(93)	37	(80)	19
Unrealized (loss) gain on available-for-sale securities, net of tax of $60 and $29 for the three months ended September 30, 2014 and 2013, respectively and $(55) and $207 for the nine months ended September 30, 2014 and 2013, respectively	(95)	(48)	90	91
Other comprehensive (loss) income	(188)	(11)	10	110
Comprehensive income	36,807	21,291	78,564	50,380
Comprehensive loss (income) attributable to noncontrolling interests	345	(213)	267	164
Comprehensive income attributable to common stockholders	$ 37,152	$ 21,078	$ 78,831	$ 50,544