Stock-Based Compensation (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	$ 3,000,000	$ 3,700,000
Additional disclosures
Proceeds from exercise of stock options	5,375,000	5,702,000
Tax benefit from exercise of stock options	3,021,000	5,500,000
Stock options
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	1,800,000	2,900,000
Stock option activity
Options outstanding at the beginning of the period (in shares)	4,604,000
Granted (in shares)	3,000
Exercised (in shares)	(514,067)	(700,000)
Forfeited (in shares)	(121,000)
Expired (in shares)	(1,000)
Options outstanding at the end of the period (in shares)	3,971,000
Options expected to vest at the end of the period (in shares)	1,502,000
Options exercisable at the end of the period (in shares)	2,429,000
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)	$ 10.46
Forfeited (in dollars per share)	$ 22.28
Expired (in dollars per shares)	$ 5.81
Options outstanding at the end of the period (in dollars per share)	$ 14.24
Options expected to vest at the end of the period (in dollars per share)	$ 22.98
Options exercisable at the end of the period (in dollars per share)	$ 8.55
Stock options, Weighted Average Remaining Contractual Terms
Options outstanding at the end of the period	4 years 6 months 4 days
Options expected to vest at the end of the period	6 years 3 months 4 days
Options exercisable at the end of the period	3 years 3 months 7 days
Stock options, Aggregate Intrinsic Value
Options outstanding at the end of the period	53,419,000
Options expected to vest at the end of the period	7,261,000
Options exercisable at the end of the period	45,970,000
Assumptions used to determine fair value of options granted
Risk-free interest rate (as a percent)	0.67%
Expected volatility (as a percent)	40.05%
Expected life	4 years 5 months 19 days
Additional disclosures
Common stock issued upon exercise of stock options (in shares)	514,067	700,000
Proceeds from exercise of stock options	5,375,000	5,702,000
Tax benefit from exercise of stock options	$ 3,021,000	$ 5,500,000