Stockholders' Equity (Schedule of Stock Based Compensation Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	$ 22,635	$ 15,141	$ 69,180	$ 42,465
Less: Income tax benefit	(9,242)	(5,746)	(27,114)	(15,119)
Total stock-based compensation, net of taxes	13,393	9,395	42,066	27,346
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	3,579	3,312	11,045	10,518
Deferred Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	0	0	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	20,159	12,628	58,621	31,276
1999 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	1,458	1,142	4,323	4,192
Capitalized Internal Use Software [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation before income taxes	(2,561)	(1,941)	(6,694)	(5,406)
Cost of Revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	684	634	2,251	1,779
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	6,628	4,927	21,647	14,059
Sales and Marketing Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	10,896	6,951	32,024	19,112
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of stock-based compensation on income	$ 4,427	$ 2,629	$ 13,258	$ 7,515