STOCK-BASED COMPENSATION - NON-OPTIONS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015
Other stock-based compensation
Contractual term of awards	10 years
Minimum
Other stock-based compensation
Continuous service period for awards to vest	1 year
Maximum
Other stock-based compensation
Continuous service period for awards to vest	3 years
Stock appreciation rights
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	367,805
Granted (in shares)	63,340
Exercised (in shares)	(7,000)
Outstanding at the end of the period (in shares)	424,145	367,805
Exercisable at the end of the period (in shares)	269,987
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 62.58
Granted (in dollars per share)	83.29
Exercised (in dollars per share)	30.96
Non-vested at the end of the period (in dollars per share)	66.19	$ 62.58
Exercisable at the end of the period (in dollars per share)	$ 63.62
Other than stock options, weighted-average remaining contractual life (in years)
Outstanding at the end of the period	6 years 7 months 6 days
Exercisable at the end of the period	5 years 7 months 6 days
Aggregate Intrinsic Value
Intrinsic value on outstanding shares	$ 5,404
Intrinsic value on exercisable shares	$ 3,928
Other stock-based compensation
Fair value granted (in dollars per share)	$ 29.76	$ 18.35	$ 24.42
Total intrinsic value	$ 200	$ 300	$ 200
Unrecognized compensation expense	$ 2,000
Weighted-average vesting period (years)	1 year 8 months 12 days
Restricted stock
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	176,522
Granted (in shares)	44,890
Vested (in shares)	(54,603)
Outstanding at the end of the period (in shares)	166,809	176,522
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 63.46
Granted (in dollars per share)	83.29
Vested (in dollars per share)	64.08
Non-vested at the end of the period (in dollars per share)	$ 68.60	$ 63.46
Other stock-based compensation
Unrecognized compensation expense	$ 5,400
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)	31,380
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)	13,510
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)	210,178
Granted (in shares)	29,830
Vested (in shares)	(45,774)
Expired (in shares)	(29,550)
Outstanding at the end of the period (in shares)	164,684	210,178
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 63.78
Granted (in dollars per share)	68.47
Vested (in dollars per share)	65.57
Expired (in dollars per share)	68.18
Non-vested at the end of the period (in dollars per share)	$ 68.53	$ 63.78
Other stock-based compensation
Unrecognized compensation expense	$ 1,400
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)	$ 53.65
Contractual term of awards	3 years
Continuous service period for awards to vest	3 years