Stockholders' Equity (Details Textuals) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Contribution Benefit Plans Disclosures [Line Items]
Total compensation expense	$ 33,003,000	$ 29,310,000	$ 33,190,000
Employee Stock Purchase Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Maximum number of common stock shares authorized for issuance under Plan	11,900,000
Shares available for future awards	1,601,230
Employer contribution rate	75.00%
Total compensation expense	6,500,000	5,700,000	4,800,000
401(k) Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employer contribution rate	100.00%
Employer's matching contributions	$ 9,000,000	$ 8,000,000	$ 7,100,000
Maximum [Member] | Employee Stock Purchase Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employee contribution rate	10.00%
Maximum [Member] | 401(k) Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employee contribution rate	6.00%