Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 14,783	$ 8,367	$ 28,968	$ 13,817
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment, net of tax of $11 for the three and six months ended June 30, 2013	(18)		(18)
Unrealized (loss) gain on available-for-sale securities, net of tax of $57 and $64 for the three months ended June 30, 2013 and 2012, respectively and $178 and $23 for the six months ended June 30, 2013 and 2012, respectively	(94)	96	139	35
Other comprehensive (loss) income	(112)	96	121	35
Comprehensive income	14,671	8,463	29,089	13,852
Allocation of comprehensive income to preferred stockholders				(64)
Comprehensive income attributable to noncontrolling interests	602		377
Comprehensive income attributable to common stockholders	$ 15,273	$ 8,463	$ 29,466	$ 13,788