FINANCING ARRANGEMENTS: (Details) - USD ($)	6 Months Ended		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2015	Jan. 28, 2016	Jul. 31, 2014
Long-term debt
Net carrying amount of long-term debt	$ 120,060,000		$ 120,002,000
Less current portion	0		(2,000)
Long-term debt	$ 120,060,000		120,000,000
Senior Notes | Convertible senior notes
Long-term debt
Interest rate percentage	5.00%	5.00%			5.00%
Net carrying amount of long-term debt	$ 0		$ 0
Long-term debt, additional disclosures
Debt face amount					$ 172,500,000
Interest expense related to contractual interest coupon		$ 400,000
Interest cost related to amortization of the discount		$ 300,000
Senior Notes | Senior term notes - 5.75%
Long-term debt
Interest rate percentage	5.75%		5.75%
Net carrying amount of long-term debt	$ 0		$ 120,000,000
Long-term debt, additional disclosures
Debt face amount	$ 120,000,000
Senior Notes | Senior term notes - 5.50%
Long-term debt
Interest rate percentage	5.50%
Net carrying amount of long-term debt	$ 120,060,000		$ 0
Long-term debt, additional disclosures
Debt face amount	123,000,000.0
Unamortized discount	3,000,000
Unamortized debt discount	$ (2,940,000)
Equipment and leasehold notes payable
Long-term debt
Interest rate percentage, minimum	4.90%		4.90%
Interest rate percentage, maximum	8.75%		8.75%
Net carrying amount of long-term debt	$ 0		$ 2,000
Revolving Credit Facility
Long-term debt
Net carrying amount of long-term debt	0		0
Long-term debt, additional disclosures
Debt face amount	400,000,000
Amount outstanding	0		0
Outstanding standby letters of credit	1,600,000		2,100,000
Revolving credit facility remaining borrowing capacity	398,400,000		$ 397,900,000
Maximum borrowing capacity	$ 400,000,000.0
Revolving Credit Facility | Subsequent Event
Long-term debt, additional disclosures
Debt face amount				$ 200,000,000
Revolving credit facility remaining borrowing capacity				$ 198,400,000