Stockholders' Equity (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Contribution Benefit Plans Disclosures [Line Items]
Shares available for future awards	11,300,000
Total compensation expenses	$ 29,310,000	$ 33,190,000	$ 36,091,000
Employee Stock Purchase Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Maximum number of common stock shares authorized for issuance under Plan	9,900,000
Shares available for future awards	462,131
Total compensation expenses	5,700,000	4,800,000	3,500,000
Employee Stock Purchase Plan [Member] | Maximum [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employee Contribution Rate	10.00%
Employer Contribution Rate	75.00%
Benefit Plan, 401K [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employer's matching contributions	$ 8,000,000	$ 7,100,000	$ 5,700,000
Benefit Plan, 401K [Member] | Maximum [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employee Contribution Rate	6.00%
Employer Contribution Rate	100.00%