STOCK-BASED COMPENSATION - NON-OPTIONS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Stock appreciation rights
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	424,145
Granted (in shares)	71,262
Exercised (in shares)	(241,421)
Forfeited (in shares)	(1,100)
Outstanding at the end of the period (in shares)	252,886	424,145
Exercisable at the end of the period (in shares)	125,152
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 66.19
Granted (in dollars per share)	87.42
Exercised (in dollars per share)	62.52
Forfeited (in dollars per share)	85.92
Non-vested at the end of the period (in dollars per share)	75.60	$ 66.19
Exercisable at the end of the period (in dollars per share)	$ 71.59
Other than stock options, weighted-average remaining contractual life (in years)
Outstanding at the end of the period	7 years 3 months 18 days
Exercisable at the end of the period	6 years 2 months 12 days
Aggregate Intrinsic Value
Intrinsic value on outstanding shares	$ 4,360
Intrinsic value on exercisable shares	$ 2,659
Other stock-based compensation
Fair value granted (in dollars per share)	$ 29.17	$ 29.76	$ 18.35
Total intrinsic value	$ 6,400	$ 200	$ 300
Unrecognized compensation expense	$ 2,000
Weighted-average vesting period (years)	1 year 9 months 18 days
Contractual term of awards	10 years
Stock appreciation rights | Minimum
Other stock-based compensation
Continuous service period for awards to vest	1 year
Stock appreciation rights | Maximum
Other stock-based compensation
Continuous service period for awards to vest	3 years
Restricted stock
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	166,810
Granted (in shares)	50,380
Vested (in shares)	(69,440)
Forfeited (in shares)	(2,967)
Outstanding at the end of the period (in shares)	144,783	166,810
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 68.60
Granted (in dollars per share)	87.42
Vested (in dollars per share)	72.99
Forfeited (in dollars per share)	73.55
Non-vested at the end of the period (in dollars per share)	$ 72.94	$ 68.60
Other stock-based compensation
Unrecognized compensation expense	$ 5,000
Weighted-average vesting period (years)	3 years
Restricted stock | Officers and Certain Employees
Non-vested other than stock options, number of shares
Granted (in shares)	36,170
Other stock-based compensation
Vesting period	3 years
Holding period of awards as a vesting condition	2 years
Vesting (as a percent)	33.00%
Restricted stock | Non Executive Directors
Non-vested other than stock options, number of shares
Granted (in shares)	14,210
Other stock-based compensation
Vesting period	1 year
Vesting (as a percent)	50.00%
Percentage of shares granted to non-executive directors, vesting one year after date of grant	50.00%
Performance stock
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	233,845
Granted (in shares)	68,020
Vested (in shares)	(70,046)
Forfeited (in shares)	(13,030)
Non-attainment (in shares)	(34,125)
Outstanding at the end of the period (in shares)	184,664	233,845
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 61.07
Granted (in dollars per share)	76.20
Vested (in dollars per share)	68.83
Forfeited (in dollars per share)	60.76
Non-attainment (in dollars per share)	71.77
Non-vested at the end of the period (in dollars per share)	$ 61.75	$ 61.07
Other stock-based compensation
Unrecognized compensation expense	$ 1,500
Weighted-average vesting period (years)	1 year 9 months 18 days
Earn out basis if no goals are met (as a percent)	0.00%
Earn out basis if some goals are met (as a percent)	100.00%
Earn out basis if all goals are met (as a percent)	200.00%
Performance stock | Vesting upon achievement of annual growth in Net GEOs
Other stock-based compensation
Vesting (as a percent)	50.00%
Performance stock | Vesting upon achievement of annual growth in Net TSR
Other stock-based compensation
Vesting (as a percent)	50.00%
Gold Equivalent Ounces Shares
Other stock-based compensation
Contractual term of awards	5 years
Total Shareholder Return Shares
Other stock-based compensation
Fair value granted (in dollars per share)	$ 64.67
Contractual term of awards	3 years
Continuous service period for awards to vest	3 years