Stockholders' Equity (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee and non-employee stock option exercise data
Employee and non-employee stock options, Number of options exercised (in shares)	575,944	837,690	3,335,114
Cash received from options exercised	$ 14,290	$ 24,398	$ 85,427
Total intrinsic value of options exercised	15,508	30,644	102,905
Tax benefits realized from options exercised	$ 3,054	$ 11,347	$ 23,826