Profit Sharing Plan and Annual Cash Bonuses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangements [Abstract]
Maximum percentage of compensation employee is allowed to contribute	15.00%
Matching contributions	$ 8.6	$ 8.2	$ 8.5
Bonus expense, cash	$ 0.0	$ 16.8	$ 20.7

The amount of payment into the fund established for purposes of making future disbursements to the individual in accordance with the terms and understanding of the deferred compensation arrangement.

No definition available.

Name:	us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration