Borrowing Arrangements (Details) $ in Thousands			9 Months Ended
	Feb. 20, 2015 USD ($)	Oct. 02, 2012 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)
Borrowing arrangements
Total debt obligations			$ 246,992	$ 253,400
Less: Current portion under Senior Credit Facility and other debt obligations			15,974	15,567
Total long-term borrowings			231,018	237,833
Senior credit facility, net of discount
Borrowing arrangements
Total debt obligations			244,905	251,010
Senior Credit Facility
Maximum borrowing capacity		$ 450,000
Period after end of each fiscal year mandatory repayment of principal required to be made		90 days
Repayment of mandatory principal					$ 7,940
Credit facility outstanding	$ 147,299
Available borrowing capacity			89,600
Current borrowing capacity			$ 89,600
Senior credit facility, net of discount | Maximum
Senior Credit Facility
Total debt to EBITDA ratio that is required to be maintained			4.0
Senior credit facility, net of discount | Maximum | Period end of each fiscal quarter ending after 1st October 2015 through 30th September 2016
Senior Credit Facility
Total debt to EBITDA ratio that is required to be maintained			3.75
Senior credit facility, net of discount | Maximum | End of each fiscal quarter ending after October 1, 2016
Senior Credit Facility
Total debt to EBITDA ratio that is required to be maintained			3.5
Senior credit facility, net of discount | Minimum
Senior Credit Facility
Fixed charge coverage ratio that is required to be maintained			1.25
Senior credit facility, net of discount | Base rate loans | Federal funds
Senior Credit Facility
Interest rate margin on variable rate basis (as a percent)			0.50%
Senior credit facility, net of discount | Base rate loans | LIBOR
Senior Credit Facility
Interest rate margin on variable rate basis (as a percent)			1.00%
Revolving credit facility
Senior Credit Facility
Maximum borrowing capacity	200,000	$ 200,000
Aggregate additional principal amount	100,000
Letter of credit facility
Senior Credit Facility
Maximum borrowing capacity	100,000	100,000
Credit facility outstanding	53,449
Swing-Line Loan Facility
Senior Credit Facility
Maximum borrowing capacity	20,000
Term loan facility
Senior Credit Facility
Maximum borrowing capacity	200,000	$ 250,000
Restated Secured Credit Facility
Senior Credit Facility
Maximum borrowing capacity	400,000
Amount borrowed	10,400
Amortization of principal in the first year	15,000
Amortization of principal in the second year	15,000
Amortization of principal in the third year	20,000
Amortization of principal in the fourth year	20,000
Amortization of principal in the fifth year	20,000
Amortization of principal in the sixth year	$ 110,000
Letters of credit outstanding			$ 52,349,000
Borrowings excluding debt discount			246,800
Less: Discount on debt			1,895
Losses on the extinguishment of debt related to debt issuance costs			634
Other debt obligations
Borrowing arrangements
Total debt obligations			$ 2,087	$ 2,390