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 Comprehensive Income [Abstract]
Net income	$ 79,756	$ 48,231	$ 213,138	$ 135,697
Other comprehensive income (loss):
Foreign currency translation adjustments	2,950	3,770	(4,810)	740
Change in unrealized gain on investments, net of income tax expense of $1,532, $425, $629 and $538 for the three and nine months ended September 30, 2013 and 2012, respectively	2,571	821	1,016	1,002
Other comprehensive income (loss)	5,521	4,591	(3,794)	1,742
Comprehensive income	$ 85,277	$ 52,822	$ 209,344	$ 137,439