Other Obligations (Details 1) - USD ($)	Feb. 21, 2014	Oct. 16, 2017	Sep. 30, 2017	Jan. 31, 2017	Dec. 31, 2016	Sep. 09, 2016	Jan. 23, 2015
Interest and Facility Fee Discussion
Outstanding letters of credit under the Credit Facility			$ 22,900,000
Reduction of letters of credit			(44,600,000)
Credit Agreement and the A/R Securitization Program
Line of Credit Facility [Line Items]
Borrowing capacity allowed			402,100,000
Total Liquidity			523,000,000
Interest and Facility Fee Discussion
Outstanding letters of credit under the Credit Facility			22,900,000
Unamortized debt issuance costs			5,300,000		$ 7,700,000
Reduction of letters of credit			(44,600,000)
A/R Securitization Program
Line of Credit Facility [Line Items]
Maximum amount under senior secured revolving credit facility			25,000,000	$ 70,000,000			$ 75,000,000
Borrowing capacity allowed			8,900,000
Interest and Facility Fee Discussion
Outstanding letters of credit under the Credit Facility			16,100,000
Outstanding borrowings			0
Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Borrowing capacity allowed						$ 400,000,000
Debt Instrument Term	5 years
Interest and Facility Fee Discussion
Outstanding letters of credit under the Credit Facility		$ 0	6,800,000			$ 250,000,000
Outstanding borrowings			$ 0