Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 22,545	$ 18,471	$ 62,554	$ 48,538
Other comprehensive income (loss), net of tax:
Unrealized net gains on available-for-sale securities	26		15
Unrealized (losses) gains on hedging derivatives, net of taxes of $56 and $26 for the three months ended September 30, 2013 and 2012, respectively, and $310 and $72 for the nine months ended September 30, 2013 and 2012, respectively	(75)	33	448	95
Comprehensive income	$ 22,496	$ 18,504	$ 63,017	$ 48,633