LONG-TERM DEBT: (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Mar. 10, 2014
Long-term debt
Total long-term debt and capital leases	$ 184,802	$ 192,856
Less current installments	32,262	32,243
Less deferred debt financing costs	2,416	2,716
Long-term debt, excluding current installments and deferred debt financing costs	150,124	157,897
Long-term debt	150,124	157,897
LIBOR rate (as a percent)			0.65%
Interest rate swap | March 10, 2014 derivative agreement | Cash flow hedge
Long-term debt
Fixed interest rate payable on swap (as a percent)				0.98%
Notional amount of derivative				$ 50,000
Fair market value of the derivative	0
Unrealized loss of the derivative recorded in other comprehensive income (loss)	$ 100
LIBOR | Interest rate swap | March 10, 2014 derivative agreement
Long-term debt
Long-term debt variable interest rate description	LIBOR
Credit Agreement
Long-term debt
Outstanding letters of credit			$ 2,100
Term loans
Long-term debt
Total long-term debt and capital leases	$ 177,500	185,000
Aggregate amount of borrowing commitment	300,000
Weighted-average interest rate on long-term debt (as a percent)			2.60%
Term loans | Quarterly installments payable through September 2017
Long-term debt
Required quarterly installment payments	7,500
Term loans | Quarterly installments payable through June 2018
Long-term debt
Required quarterly installment payments	11,300
Term loans | Final payment due on October 9, 2018
Long-term debt
Final payment of long-term debt	$ 106,300
Term loans | LIBOR
Long-term debt
Long-term debt basis spread on variable interest rate (as a percent)	2.00%
Revolving credit facility
Long-term debt
Aggregate amount of borrowing commitment	$ 300,000
Outstanding revolving credit borrowings	0	0
Revolving credit facility dividend restrictions amount, maximum	$ 30,000
Revolving credit facility | LIBOR
Long-term debt
Long-term debt basis spread on variable interest rate (as a percent)	2.00%
Other debt and long-term liabilities
Long-term debt
Total long-term debt and capital leases	$ 7,302	$ 7,856