Employee Benefit Plans, 401(k) plan and Deferred Compensation Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Benefit Textuals [Abstract]
Employee Contribution Matched in Percent	30.00%
Matching Contributions to Plan	$ 21.1	$ 20.7	$ 19.6
Fair value of the Pension Plans	11.3	8.4
Net plan liability	4.3	2.4
NQDC
Employee Benefit Textuals [Abstract]
Deferred compensation liability, noncurrent	27.6
Investment	27.6	21.0
Deferred compensation liability, current		$ 21.0
Other Accrued Liabilities | NQDC
Employee Benefit Textuals [Abstract]
Deferred compensation liability, noncurrent	4.9
Other Long Term Liabilities | NQDC
Employee Benefit Textuals [Abstract]
Deferred compensation liability, noncurrent	22.7
Prepaid expenses and other current assets | NQDC
Employee Benefit Textuals [Abstract]
Investment	4.9
Restricted Stock Units (RSUs) | NQDC
Employee Benefit Textuals [Abstract]
Investment	$ 22.7