Stockholders' Equity (Schedule of Stock Based Compensation Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	$ 20,924	$ 15,712
Less: Income tax benefit	(8,497)	(5,062)
Total stock-based compensation, net of taxes	12,427	10,650
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	3,100	3,786
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	18,728	12,120
1999 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	1,394	1,630
Capitalized Internal Use Software [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	(2,298)	(1,824)
Cost of Revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	683	555
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	6,177	5,549
Sales and Marketing Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	10,134	6,846
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	$ 3,930	$ 2,762