Stockholders' Equity (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Employee and non-employee stock option exercise data
Unrecognized compensation cost related to employee stock options	$ 0
Number of options exercised (in shares)	876,115	575,944	837,690
Cash received from options exercised	26,620	14,290	24,398
Total intrinsic value of options exercised	37,530	15,508	30,644
Tax benefits realized from options exercised	$ 9,299	$ 3,054	$ 11,347