Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 14,185	$ 5,450
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax of $120 and $41 for the three months ended March 31, 2013 and 2012, respectively	233	(61)
Other comprehensive income (loss)	233	(61)
Comprehensive income	14,418	5,389
Allocation of comprehensive income to preferred stockholders		(64)
Comprehensive income attributable to noncontrolling interests	(225)
Comprehensive income attributable to common stockholders	$ 14,193	$ 5,325