Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 21,767	$ 14,185
Other comprehensive income, net of tax:
Foreign currency translation adjustment, net of tax of ($15) for the three months ended March 31, 2014	24
Unrealized gain on available-for-sale securities, net of tax of ($40) and $120 for the three months ended March 31, 2014 and 2013, respectively	63	233
Other comprehensive income	87	233
Comprehensive income	21,854	14,418
Comprehensive loss (income) attributable to noncontrolling interests	171	(225)
Comprehensive income attributable to common stockholders	$ 22,025	$ 14,193