Stock-Based Compensation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	$ 3,100,000	$ 3,400,000	$ 6,100,000	$ 7,100,000
Additional disclosures
Proceeds from exercise of stock options			6,309,000	7,453,000
Tax benefit from exercise of stock options	1,200,000	1,300,000	4,244,000	6,800,000
Stock options
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	1,800,000	2,400,000	3,700,000	5,200,000
Stock option activity
Options outstanding at the beginning of the period (in shares)			4,757,000
Granted (in shares)			3,000
Exercised (in shares)	(200,000)	(200,000)	(712,000)	(900,000)
Forfeited (in shares)			(189,000)
Expired (in shares)			(2,000)
Options outstanding at the end of the period (in shares)	3,857,000		3,857,000
Options expected to vest at the end of the period (in shares)	1,489,000		1,489,000
Options exercisable at the end of the period (in shares)	2,328,000		2,328,000
Stock options, Weighted Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)			$ 14.11
Granted (in dollars per share)			$ 28.74
Exercised (in dollars per share)			$ 8.86
Forfeited (in dollars per share)			$ 20.15
Expired (in dollars per shares)			$ 11.26
Options outstanding at the end of the period (in dollars per share)	$ 14.82		$ 14.82
Options expected to vest at the end of the period (in dollars per share)	$ 23.72		$ 23.72
Options exercisable at the end of the period (in dollars per share)	$ 8.98		$ 8.98
Stock options, Weighted Average Remaining Contractual Terms
Options outstanding at the end of the period			4 years 3 months 25 days
Options expected to vest at the end of the period			6 years 11 days
Options exercisable at the end of the period			3 years 2 months 8 days
Stock options, Aggregate Intrinsic Value
Options outstanding at the end of the period	38,063,000		38,063,000
Options expected to vest at the end of the period	4,080,000		4,080,000
Options exercisable at the end of the period	33,876,000		33,876,000
Assumptions used to determine fair value of options granted
Risk-free interest rate (as a percent)			0.67%	0.70%
Expected volatility (as a percent)			40.05%	41.35%
Expected life			4 years 5 months 19 days	4 years 5 months 19 days
Additional disclosures
Common stock issued upon exercise of stock options (in shares)	200,000	200,000	712,000	900,000
Proceeds from exercise of stock options	900,000	1,800,000	6,300,000	7,500,000
Tax benefit from exercise of stock options	$ 1,200,000	$ 1,300,000	$ 4,200,000	$ 6,800,000