LONG-TERM DEBT: (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended		12 Months Ended
	Jul. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2015	Sep. 30, 2015	Mar. 10, 2014
Long-term debt
Total long-term debt and capital leases			$ 200,904		$ 280,087
Less current installments			32,223		32,232
Long-term debt, excluding current installments			168,681		247,855
Existing debt repaid with proceeds of term loan			79,183	$ 18,254
LIBOR rate (as a percent)						0.54%
ITO
Long-term debt
Allocated interest expense		$ 300	400	$ 1,000
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
Credit Agreement | ITO
Long-term debt
Proceeds from sale utilized to repay outstanding indebtedness	$ 55,000
Allocated interest expense			400
Credit Agreement | ITO | Maximum
Long-term debt
Maximum amount of common stock that may be repurchased			100,000
Term loans
Long-term debt
Total long-term debt and capital leases			192,500		270,000
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			$ 8,404		$ 10,087