Other Obligations (Details 2) (USD $)	0 Months Ended	3 Months Ended
	Feb. 21, 2014	Mar. 31, 2015	Feb. 11, 2013
Credit Agreement and the A/R Securitization Program
Line of Credit Facility [Line Items]
Borrowing capacity allowed		$ 539,900,000
A/R Securitization Program
Line of Credit Facility [Line Items]
Borrowing capacity allowed		39,900,000
Interest and Facility Fee Discussion
Outstanding borrowings		0
A/R Securitization Program | Maximum
Line of Credit Facility [Line Items]
Maximum amount under senior secured revolving credit facility			75,000,000
Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Term of revolving credit facility	5 years 0 months 0 days
Interest and Facility Fee Discussion
Base rate on interest on leases		LIBOR
Fronting fee payable in connection with the issuance of a letter of credit (as a percent)		0.125%
Outstanding letters of credit under the Credit Facility		0
Outstanding borrowings		0
Senior Secured Revolving Credit Facility | Minimum
Debt Agreement Ratios
EBITDA to consolidated net cash interest expense covenant ratio		150.00%
Interest and Facility Fee Discussion
Margin over base rate on lease agreement (as a percent)		2.00%
Commitment fee payable to lender (as a percent)		0.375%
Annual fee on issued letters of credit (as a percent)		2.00%
Senior Secured Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Maximum amount under senior secured revolving credit facility		500,000,000
Letters of credit that can be issued		250,000,000
Option to increase credit facility size amount		$ 200,000,000
Debt Agreement Ratios
Ratio of net secured debt to EBITDA		400.00%
Interest and Facility Fee Discussion
Margin over base rate on lease agreement (as a percent)		2.75%
Commitment fee payable to lender (as a percent)		0.50%
Annual fee on issued letters of credit (as a percent)		2.75%