LONG-TERM DEBT: (Details) (USD $)			6 Months Ended		6 Months Ended		6 Months Ended	12 Months Ended				6 Months Ended
	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2012 Interest rate swap July 25, 2011 derivative agreement	Jul. 25, 2011 Interest rate swap July 25, 2011 derivative agreement	Sep. 30, 2012 Term loan credit agreement	Mar. 31, 2012 Term loan credit agreement	Sep. 30, 2012 Capital leases and installment payment obligations	Mar. 31, 2012 Capital leases and installment payment obligations	Sep. 30, 2012 Other debt and long-term liabilities	Mar. 31, 2012 Other debt and long-term liabilities	Sep. 30, 2012 Revolving credit facility	Sep. 30, 2012 Revolving credit facility LIBOR	Sep. 30, 2012 Revolving credit facility Alternative base rate	Sep. 30, 2012 Revolving credit facility Federal Funds rate
Long-term debt
Total long-term debt and capital leases	$ 266,839,000	$ 278,222,000			$ 221,000,000	$ 224,000,000	$ 28,937,000	$ 35,726,000	$ 16,902,000	$ 18,496,000
Less current installments	22,492,000	26,336,000
Long-term debt, excluding current installments	244,347,000	251,886,000
Long-term debt stated interest rate percentage, minimum							3.00%	3.00%
Long-term debt stated interest rate percentage, maximum							8.00%	8.00%
Maximum remaining maturity period of debt							10 years	10 years
Aggregate amount of borrowing commitment					600,000,000						120,000,000
Required quarterly installment payments					1,500,000
Final payment of long-term debt due March 15, 2015					207,500,000
Long-term debt variable interest rate description					LIBOR							LIBOR	Alternative base rate	Federal Funds rate
Long-term debt basis spread on variable interest rate (as a percent)					3.00%							2.75%
Weighted-average interest rate on long-term debt (as a percent)					3.70%
Outstanding letters of credit											2,200,000
Revolving credit facility dividend restrictions amount, maximum											30,000,000
Fixed interest rate payable on swap (as a percent)				0.94%
Notional amount of derivative				150,000,000
Description of variable interest rate basis receivable on swap			LIBOR
LIBOR rate (as a percent)			0.45%
Unrealized loss of the derivative recorded in other comprehensive income (loss)			$ 1,200,000