Shareholders' Equity (Deficit) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Authorized shares	300,000,000	300,000,000
Par value of common stock (in dollars per share)	$ 0.01	$ 0.01
Shares reserved for issuance of stock options	7,455,144
Stock options exercised	243,502	386,300	745,938
Proceeds from exercise of stock options	$ 6.7	$ 16.4	$ 17.0
Common stock activity roll forward
Common stock outstanding at the beginning of the period (in shares)	67,780,410	68,309,431	70,533,515
Stock options exercised	243,502	386,300	745,938
Shares issued	72,590	49,897	110,953
Shares forfeited	(132,393)	(29,783)	(305,678)
Shares repurchased	(1,171,141)	(935,435)	(2,775,297)
Common stock outstanding at the end of the period (in shares)	66,792,968	67,780,410	68,309,431
Shares issued to Board of Directors [Member]
Common stock activity roll forward
Shares issued	10,346
Net share settlement [Member]
Common stock activity roll forward
Shares issued	7,719
Deferred Compensation, Share-based Payments [Member]
Common stock activity roll forward
Shares issued	54,525