Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Stock-Based Compensation
Stock-based compensation expense recognized related to stock compensation plans	$ 3,800	$ 3,300	$ 7,100	$ 6,200
Assumptions used to determine fair value of options granted
Weighted-average grant-date fair value per share of the stock options granted	$ 6.23	$ 5.92
Expected life			4 years 10 months 21 days	4 years 9 months 22 days
Additional disclosures
Proceeds from exercise of stock options			$ 3,412	$ 3,076
Tax benefit from exercise of stock options			1,456
Stock options
Stock-Based Compensation
Stock-based compensation expense recognized related to stock compensation plans	$ 1,700	$ 1,800	$ 3,100	$ 3,600
Stock option activity
Options outstanding at the beginning of the period (in shares)			4,101,000
Granted (in shares)			1,254,000
Exercised (in shares)	(29,512)	(54,208)	(472,097)	(316,041)
Forfeitures (in shares)			(335,000)
Expired (in shares)			(272,000)
Options outstanding at the end of the period (in shares)	4,276,000		4,276,000
Options expected to vest at the end of the period (in shares)	2,611,000		2,611,000
Options exercisable at the end of the period (in shares)	1,606,000		1,606,000
Stock options, Weighted Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)			$ 18.72
Granted (in dollars per share)			16.78
Exercised (in dollars per share)			7.23
Forfeitures (in dollars per share)			22.85
Expired (in dollars per shares)			25.74
Options outstanding at the end of the period (in dollars per share)	$ 18.65		18.65
Options expected to vest at the end of the period (in dollars per share)	19.57		19.57
Options exercisable at the end of the period (in dollars per share)	$ 17.13		$ 17.13
Stock options, Weighted Average Remaining Contractual Terms
Options outstanding at the end of the period			4 years 11 months 19 days
Options expected to vest at the end of the period			6 years 1 month 28 days
Options exercisable at the end of the period			3 years
Stock options, Aggregate Intrinsic Value
Options outstanding at the end of the period	$ 7,249		$ 7,249
Options expected to vest at the end of the period	489		489
Options exercisable at the end of the period	6,750		$ 6,750
Assumptions used to determine fair value of options granted
Risk-free interest rate (as a percent)			1.65%	1.50%
Expected volatility (as a percent)			38.28%	37.27%
Additional disclosures
Proceeds from exercise of stock options	100	$ 600	$ 3,400	$ 3,100
Tax benefit from exercise of stock options	7,000	0	1,500	900
Unrecognized stock-based compensation, stock options	13,600		$ 13,600
Weighted-average period over which compensation will be recognized			1 year 4 months 17 days
Total intrinsic value of options exercised	300	400	$ 5,700	3,300
Restricted Stock Units
Stock-Based Compensation
Stock-based compensation expense recognized related to stock compensation plans	2,200	1,500	4,000	2,500
Additional disclosures
Unrecognized stock-based compensation, restricted stock	$ 19,300		$ 19,300
Weighted-average period over which compensation will be recognized			1 year 6 months 15 days
Restricted Stock
Stock-Based Compensation
Stock-based compensation expense recognized related to stock compensation plans		$ 100	$ 0	$ 100