Stock-Based Compensation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	$ 3,300,000	$ 3,100,000	$ 6,200,000	$ 6,100,000
Excess tax benefit from stock-based compensation			854,000	4,244,000
Income tax expense (benefit)	4,593,000	6,692,000	6,982,000	11,276,000
Assumptions used to determine fair value of options granted
Weighted-average grant-date fair value per share of the stock options granted			$ 5.92	$ 9.71
Additional disclosures
Proceeds from exercise of stock options			3,076,000	6,309,000
Tax benefit from exercise of stock options			854,000	4,200,000
Employee Stock Option [Member]
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	1,800,000	1,800,000	3,600,000	3,700,000
Stock option activity
Options outstanding at the beginning of the period (in shares)			4,273,000
Granted (in shares)			58,000
Exercised (in shares)	(100,000)	(200,000)	(316,000)	(700,000)
Forfeitures (in shares)			(207,000)
Expired (in shares)			(117,000)
Options outstanding at the end of the period (in shares)	3,691,000		3,691,000
Options expected to vest at the end of the period (in shares)	1,743,000		1,743,000
Options exercisable at the end of the period (in shares)	1,907,000		1,907,000
Stock options, Weighted Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)			$ 17.53
Granted (in dollars per share)			$ 19.96
Exercised (in dollars per share)			$ 9.90
Forfeitures (in dollars per share)			$ 23.50
Expired (in dollars per shares)			$ 22.69
Options outstanding at the end of the period (in dollars per share)	$ 17.72		$ 17.72
Options expected to vest at the end of the period (in dollars per share)	$ 22.69		$ 22.69
Options exercisable at the end of the period (in dollars per share)	$ 13.06		$ 13.06
Stock options, Weighted Average Remaining Contractual Terms
Options outstanding at the end of the period	4 years 6 months
Options expected to vest at the end of the period	6 years 11 days
Options exercisable at the end of the period	3 years 22 days
Stock options, Aggregate Intrinsic Value
Options outstanding at the end of the period	18,094,000		18,094,000
Options expected to vest at the end of the period	896,000		896,000
Options exercisable at the end of the period	17,172,000		17,172,000
Assumptions used to determine fair value of options granted
Risk-free interest rate (as a percent)			1.50%	0.67%
Expected volatility (as a percent)			37.27%	40.05%
Expected life			4 years 9 months 22 days	4 years 5 months 19 days
Additional disclosures
Proceeds from exercise of stock options	600,000	900,000	3,100,000	6,300,000
Tax benefit from exercise of stock options		1,200,000	900,000	4,200,000
Unrecognized stock-based compensation	11,100,000		11,100,000
Weighted-average period over which compensation will be recognized			1 year 3 months 18 days
Total intrinsic value of options exercised	400,000	4,000,000	3,300,000	13,900,000
Restricted Stock Units R S U [Member]
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	1,500,000	1,200,000	2,500,000	2,100,000
Stock options, Aggregate Intrinsic Value
Options outstanding at the end of the period					14,429,000
Additional disclosures
Unrecognized stock-based compensation	11,400,000		11,400,000
Weighted-average period over which compensation will be recognized			1 year 8 months 12 days
Restricted Stock [Member]
Stock-based compensation
Stock-based compensation expense recognized related to stock compensation plans	$ 100,000		$ 100,000