Long-term Debt - Credit Agreement (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($) Rate	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Net leverage ratio	3.00		3.00
Payments of Financing Costs		$ 1,100
Debt financing and related expenses			$ 0	$ (6,640)	$ 0
Write off of Deferred Debt Issuance Cost		$ 2,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate | Rate	1.50%
Incremental debt commitments capacity	$ 200,000		200,000
Bank debt and receivables facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount	284,900		$ 284,900	332,100
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date			Sep. 20, 2022
Line of Credit Facility, Maximum Borrowing Capacity	300,000		$ 300,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	125,000		125,000
Revolving Credit Facility, Amount Outstanding	0		0	10,800
Revolving Credit Facility, Remaining Borrowing Capacity	284,900		284,900	274,300
Letters of credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	40,000		40,000
Letters of Credit Outstanding, Amount	$ 15,100		$ 15,100	$ 14,900