Debt (Details) (USD $)	3 Months Ended	12 Months Ended					0 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended								12 Months Ended
	Mar. 31, 2014 item	Mar. 31, 2014 item	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2014 Minimum	Mar. 31, 2014 Maximum	Mar. 17, 2014 8.875% Senior Notes due 2018	Mar. 31, 2012 8.875% Senior Notes due 2018	Mar. 31, 2013 8.875% Senior Notes due 2018	Aug. 24, 2011 8.875% Senior Notes due 2018	Mar. 17, 2014 6.50% Senior Notes due 2019	Mar. 31, 2014 6.50% Senior Notes due 2019 item	Mar. 31, 2014 6.50% Senior Notes due 2019 Prior to October 1, 2016	Mar. 31, 2014 6.50% Senior Notes due 2019 Twelve-month period beginning on October 1, 2016	Mar. 31, 2014 6.50% Senior Notes due 2019 Twelve-month period beginning on October 1, 2018 and at any time thereafter	Mar. 31, 2014 6.50% Senior Notes due 2019 Maximum Prior to October 1, 2016	Mar. 31, 2013 Revolving credit facilities	Mar. 31, 2014 Revolving credit facilities	Jun. 29, 2013 Revolving credit facilities	Mar. 31, 2014 U.S. revolving credit facility	Mar. 31, 2014 U.S. revolving credit facility Maximum	Mar. 31, 2014 Canadian revolving credit facility	Mar. 31, 2014 Canadian revolving credit facility Maximum
Debt
Long-term debt	$ 694,500,000	$ 694,500,000	$ 708,790,000						$ 643,790,000			$ 575,000,000					$ 65,000,000	$ 119,500,000
Less portion classified as current	(119,500,000)	(119,500,000)	(65,000,000)
Long-term debt, less current portion	575,000,000	575,000,000	643,790,000
Proceeds from issuance of debt		575,000,000
Net proceeds from issuance of debt											563,300,000
Debt redemption / repurchase		672,361,000		158,012,000			643,800,000	158,000,000
Interest rate (as a percent)							8.875%			8.875%		6.50%
Payment of call premium							28,600,000
write-off of unamortized deferred financing costs		8,125,000	599,000	3,091,000			8,100,000
Loss on extinguishment of debt	36,697,000	36,697,000	599,000	4,861,000			36,700,000	4,900,000									600,000
Principal amount of notes repurchased								156,200,000
Estimated fair market value of debt												570,700,000
Percentage of aggregate principal amount that may be redeemed																35.00%
Redemption price as a percentage of principal amount upon occurrence of change of control												101.00%	106.50%	103.25%	101.625%
Number of preceding quarters for which fixed charge coverage ratio is measured												4
Minimum fixed charge coverage ratio required to make restricted payments												1.75
Amount included in the general basket of restricted payments												75,000,000
Actual fixed charge coverage ratio	2.8	2.8										2.8
Amount of distribution permitted on achievement of condition related to fixed charge coverage ratio												207,100,000
Percentage of aggregate principal amount of notes that holders can request for accelerated payment in case of an event of default												25.00%
Period upon occurrence of change of control used to determine redemption of debt												90 days
Maximum borrowing capacity																		400,000,000	400,000,000	200,000,000		200,000,000
Amount by which maximum borrowing capacity may be expanded in additional commitments																				100,000,000		100,000,000
Borrowing base collateral																		396,400,000
Amount included in aggregate borrowing base under the Credit Facilities due to a first-priority lien on fixed assets granted to the lenders																		150,000,000
Minimum amount of release from the first-priority lien for reduction in fixed assets amount on a dollar-for-dollar basis																		50,000,000
Minimum fixed charge coverage ratio required to be maintained when excess availability under facility is less than 15% of the aggregate amount of availability																				1.1		1.1
Level of available Credit Facilities under both the U.S. revolving facility and the Canadian revolving credit facility at the end of each fiscal quarter before the maintenance of a fixed charge coverage ratio of 1.1 to 1.0 is not required																					15.00%		15.00%
Period of consecutive time that excess availability exceeds 15% to release quarterly testing of the 1.1 to 1.0 fixed charge coverage ratio																				30 days		30 days
Borrowings outstanding	119,500,000	119,500,000	65,000,000														65,000,000	119,500,000
Weighted average interest rate (as a percent)																	3.69%	3.56%
Letters of credit issued	4,800,000	4,800,000															3,300,000	4,800,000
Number of independent assets or operations other than investments in subsidiaries	0	0
Restricted assets	$ 0	$ 0
Fixed charge coverage ratio required to incur additional debt obligations						2.0
Fixed charge coverage ratio permitted for making restricted payments					1.75