Stockholders' Equity (Schedule of Stock Based Compensation Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	$ 25,621	$ 11,612	$ 46,545	$ 27,324
Less: Income tax benefit	(9,375)	(4,311)	(17,872)	(9,373)
Total stock-based compensation, net of taxes	16,246	7,301	28,673	17,951
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	4,366	3,420	7,466	7,206
Deferred Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	1,885	1,885	1,885	1,885
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	19,734	6,528	38,462	18,648
1999 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	1,471	1,420	2,865	3,050
Capitalized Internal Use Software [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	(1,835)	(1,641)	(4,133)	(3,465)
Cost of Revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	884	590	1,567	1,145
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	8,842	3,583	15,019	9,132
Sales and Marketing Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	10,994	5,315	21,128	12,161
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	$ 4,901	$ 2,124	$ 8,831	$ 4,886