Stock-Based Compensation (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 15,058,000	$ 13,058,000	$ 53,155,000	$ 39,654,000
Stock-based compensation expense related to modification of the vesting and exercise terms for a certain employee's equity awards	0		1,100,000
Capitalized stock-based compensation expense	400,000	500,000	1,200,000	1,600,000
Vesting period			4 years
Accelerated recognition of stock-based compensation expense related to awards granted to retirement eligible employees, additional expense recognized			7,500,000
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)			$ 19.15
Total unrecognized compensation expense	39,300,000		39,300,000
Total compensation cost not yet recognized, period for recognition			2 years
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 86,700,000		$ 86,700,000
Total compensation cost not yet recognized, period for recognition			2 years
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock purchased during bi-annual offer			85.00%
Number of shares purchased by employees under the Employee Stock Purchase Plan			57,000
Employee stock purchase plan, fair value per share (in dollars per share)			$ 13.41
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Expiration period			10 years
Number of shares issuable under stock incentive plan	16,600,000		16,600,000