FINANCING ARRANGEMENTS: Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	9 Months Ended
	Apr. 30, 2018	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2018	Feb. 28, 2018	Jun. 30, 2017
Debt Instrument [Line Items]
Long-term debt		$ 90,000,000	$ 90,000,000	$ 90,000,000		$ 120,599,000
Line of Credit | Revolving Credit Facility | Revolving credit facility (March 2018)
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 260,000,000	260,000,000	260,000,000
Debt term		5 years
Line of credit, increase limit		$ 150,000,000	150,000,000	150,000,000
Long-term debt		90,000,000	90,000,000	90,000,000		0
Unused borrowing capacity, amount		$ 168,400,000	$ 168,400,000	$ 168,400,000
Interest rate percentage		3.55%	3.55%	3.55%
Proceeds from lines of credit		$ 90,000,000
Line of Credit | Revolving Credit Facility | Revolving credit facility (March 2018) | Subsequent Event
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 295,000,000.0
Line of credit, limit increase	$ 35,000,000
Line of Credit | Revolving Credit Facility | Revolving credit facility (March 2018) | Minimum
Debt Instrument [Line Items]
Commitment fee percentage		0.25%
Line of Credit | Revolving Credit Facility | Revolving credit facility (March 2018) | Maximum
Debt Instrument [Line Items]
Commitment fee percentage		0.40%
Line of Credit | Revolving Credit Facility | Revolving credit facility (March 2018) | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		1.25%
Line of Credit | Revolving Credit Facility | Revolving credit facility (March 2018) | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		1.85%
Line of Credit | Revolving Credit Facility | Revolving credit facility (June 2011)
Debt Instrument [Line Items]
Long-term debt		$ 0	$ 0	$ 0		0
Unused borrowing capacity, amount						198,500,000
Debt face amount					$ 200,000,000
Interest expense, debt			$ 100,000	$ 100,000
Interest rate percentage		0.00%	0.00%	0.00%
Line of Credit | Letter of Credit | Revolving credit facility (March 2018)
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 30,000,000	$ 30,000,000	$ 30,000,000
Long-term line of credit		1,600,000	1,600,000	1,600,000
Line of Credit | Letter of Credit | Revolving credit facility (June 2011)
Debt Instrument [Line Items]
Long-term line of credit					$ 1,500,000
Line of Credit | Swingline Loan | Revolving credit facility (March 2018)
Debt Instrument [Line Items]
Maximum borrowing capacity		30,000,000	30,000,000	30,000,000
Senior Notes | Senior Term Notes
Debt Instrument [Line Items]
Long-term debt		0	$ 0	$ 0		$ 120,599,000
Interest expense, debt		$ 1,700,000
Interest rate percentage		5.50%	5.50%	5.50%
Repurchase amount		$ 124,200,000	$ 124,200,000	$ 124,200,000
Unamortized premium		1,200,000	$ 1,200,000	$ 1,200,000
Repayments of debt		$ 34,200,000