Other Obligations (Details 1) - USD ($)		3 Months Ended		6 Months Ended
	Feb. 21, 2014	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jul. 27, 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		$ 50,600,000		$ 50,600,000
Outstanding borrowings						$ 28,600,000
Write off debt issuance costs		0	$ 0	702,000	$ 0
Reduction of letters of credit						$ (38,900,000)
Credit Agreement and the A/R Securitization Program
Line of Credit Facility [Line Items]
Borrowing capacity allowed		372,300,000		372,300,000
Debt Instrument Term	5 years
Total Liquidity		452,800,000		452,800,000
Interest and Facility Fee Discussion
Unamortized debt issuance costs		6,200,000		6,200,000				$ 7,700,000
Reduction of letters of credit		(16,900,000)		(16,900,000)
A/R Securitization Program
Line of Credit Facility [Line Items]
Maximum amount under senior secured revolving credit facility		22,900,000		22,900,000						$ 75,000,000
Borrowing capacity allowed		14,300,000		14,300,000
Interest and Facility Fee Discussion
Outstanding letters of credit under the Credit Facility		8,600,000		8,600,000
Outstanding borrowings		0		0
A/R Securitization Program | Maximum
Line of Credit Facility [Line Items]
Maximum amount under senior secured revolving credit facility							$ 70,000,000
Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Borrowing capacity allowed									$ 400,000,000
Interest and Facility Fee Discussion
Outstanding letters of credit under the Credit Facility		42,000,000		42,000,000					$ 250,000,000
Outstanding borrowings		$ 0		$ 0