Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 Stock Options [Member]	Jun. 30, 2013 Restricted Stock Units [Member]	Jun. 30, 2013 Employee Share Purchase Plan [Member]	Mar. 31, 2013 Employee Share Purchase Plan [Member]	Jun. 30, 2013 Stock Incentive Plan [Member]	Mar. 31, 2013 Stock Incentive Plan [Member]	Jun. 30, 2013 Supplemental Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized				3,950,000	3,700,000	11,000,000	10,750,000	500,000
Shares available for grant	2,331,500
Shares of common stock reserved for issuance	3,910,876
Total compensation cost not yet recognized	$ 35.5
Total compensation cost not yet recognized - period for recognition	1 year 9 months 18 days
Options Outstanding and Exercisable:
Options outstanding, number		767,869
Options exercisable, number		199,785
Options outstanding, weighted average exercise price		$ 39.38
Options exercisable, weighted average exercise price		$ 28.71
Options outstanding, aggregate intrinsic value		25.8
Options exercisable, aggregate intrinsic value		8.9
Options outstanding, weighted average remaining contractual term (in years)		5 years
Options exercisable, weighted average remaining contractual term (in years)		3 years 10 months 24 days
Restricted Stock Units Nonvested and Expected to Vest
Restricted stock units nonvested, number			811,509
Restricted stock units expected to vest, number			718,887
Restricted stock units nonvested, weighted average grant date per share fair value			$ 43.13
Restricted stock units expected to vest, weighted average grant date per share fair value			$ 42.67
Restricted stock units nonvested, aggregate intrinsic value			59.3
Restricted stock units expected to vest, aggregate intrinsic value			$ 52.5
Restricted stock units nonvested, weighted average remaining term to vest (in years)			1 year 4 months 24 days
Restricted stock units expected to vest, weighted average remaining term to vest (in years)			1 year 4 months 24 days