Long-term Debt - Credit Agreement (Details) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Dec. 31, 2017 USD ($) Rate	Sep. 30, 2017 USD ($)	Sep. 30, 2017	Sep. 19, 2017 USD ($) Rate	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Net leverage ratio		3.00				3.00
Payments of Financing Costs			$ 1,100
Debt financing and related expenses						$ (6,640)	$ 0	$ (1,970)
Write off of Deferred Debt Issuance Cost			$ 2,000					1,500
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate | Rate	[1],[2]	1.50%			1.625%
Incremental debt commitments capacity		$ 200,000				200,000
Revolving credit and term loan facilities [Member]
Debt Instrument [Line Items]
Payments of Financing Costs								1,800
Debt Issuance Costs, Noncurrent, Net								1,400
Debt financing and related expenses								$ 400
Bank debt and receivables facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount		$ 332,100				332,100	126,500
Senior Secured Term Loan A [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate | Rate	[1],[2]				1.625%
Debt Instrument, Face Amount					$ 275,000
Debt Instrument, Maturity Date					Jun. 30, 2020
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				1.625%
Debt Instrument, Maturity Date		Sep. 20, 2022			Jun. 30, 2020
Line of Credit Facility, Maximum Borrowing Capacity		$ 300,000			$ 500,000	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			$ 75,000	125,000
Revolving Credit Facility, Amount Outstanding		10,800				10,800	75,900
Revolving Credit Facility, Remaining Borrowing Capacity		274,300				274,300	408,200
Letters of credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		40,000				40,000
Letters of Credit Outstanding, Amount		$ 14,900				$ 14,900	$ 15,900

[1] London Interbank Offered Rate ("LIBOR")

[2] The initial interest rate spread for the amended Credit Agreement is stated as 1.625%. The interest rate spread is based upon the leverage ratio, as defined, as of the most recent determination date.