Long-Term Obligations (Details) (USD $)			12 Months Ended							12 Months Ended										1 Months Ended			1 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	May 31, 2013 Revolving credit facility	Mar. 31, 2013 Revolving credit facility	Mar. 31, 2013 Revolving credit facility Minimum	Mar. 31, 2013 Revolving credit facility Maximum	Mar. 31, 2013 Revolving credit facility LIBOR option	Mar. 31, 2013 Revolving credit facility LIBOR option Minimum	Mar. 31, 2013 Revolving credit facility LIBOR option Maximum	Mar. 31, 2013 Revolving credit facility Alternate base rate	Mar. 31, 2013 Revolving credit facility Alternate base rate Minimum	Mar. 31, 2013 Revolving credit facility Alternate base rate Maximum	May 31, 2013 Revolving credit facility Working capital facility	Mar. 31, 2013 Revolving credit facility Working capital facility	Mar. 31, 2013 Revolving credit facility Working capital facility LIBOR option	Mar. 31, 2013 Revolving credit facility Working capital facility Alternate base rate	May 31, 2013 Revolving credit facility Expansion Capital Facility	Mar. 31, 2013 Revolving credit facility Expansion Capital Facility	Mar. 31, 2013 Revolving credit facility Expansion Capital Facility LIBOR option	Jun. 30, 2012 Previous revolving credit facility	Mar. 31, 2012 Previous revolving credit facility Working capital facility	Mar. 31, 2012 Previous revolving credit facility Acquisition facility	Jun. 30, 2012 Senior Notes	Mar. 31, 2013 Senior Notes	Mar. 31, 2013 Senior Notes Minimum	Mar. 31, 2013 Other notes payable	Mar. 31, 2012 Other notes payable	Mar. 31, 2013 Other notes payable Minimum	Mar. 31, 2013 Other notes payable Maximum
Long-Term Debt
Total debt	$ 749,062,000	$ 218,711,000												$ 36,000,000				$ 441,500,000			$ 28,000,000	$ 186,000,000		$ 250,000,000		$ 21,562,000	$ 4,711,000
Less - current maturities	8,626,000	19,534,000
Long-term debt	740,436,000	199,177,000
Debt issued																							250,000,000
Maximum borrowing capacity													325,000,000	242,500,000			725,000,000	527,500,000
Fees paid related to amendment of agreement			2,100,000
Outstanding cash borrowings				477,500,000			461,500,000			16,000,000				36,000,000	20,000,000	16,000,000		441,500,000	441,500,000
Outstanding letters of credit														60,100,000
Remaining borrowing capacity														146,400,000				86,000,000
Variable interest rate base							LIBOR			base rate
Interest rate margin added to variable rate base							3.00%	2.75%	3.75%	2.00%	1.75%	2.75%
Reference rate (as a percent)							0.21%			3.25%
Commitment fees charged on unused credit (as a percent)					0.38%	0.50%
Fixed interest rate (as a percent)																								6.65%
Debt covenant terms, default trigger amount																									10,000,000
Percentage of aggregate principal amount held by trustee or holders to declare notes due and payable																									51.00%
Principal payment																				306,800,000
Leverage ratio						4.25
Actual leverage ratio				3.0
Interest coverage ratio					2.75
Actual interest coverage ratio				7.0
Repayments in semi-annual installments																								$ 25,000,000
Interest rate (as a percent)							3.21%			5.25%					3.21%	5.25%			3.21%									2.60%	4.90%