STOCK-BASED COMPENSATION - NON-OPTIONS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2019
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)	122,604
Granted (in shares)	64,100
Exercised (in shares)	(2,567)
Outstanding at the end of the period (in shares)	184,137	122,604
Exercisable at the end of the period (in shares)	76,287
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 95.57
Granted (in dollars per share)	139.84
Exercised (in dollars per share)	83.45
Non-vested at the end of the period (in dollars per share)	111.15	$ 95.57
Exercisable at the end of the period (in dollars per share)	$ 86.32
Other than stock options, weighted-average remaining contractual life (in years)
Outstanding at the end of the period	7 years 8 months 12 days
Exercisable at the end of the period	6 years 3 months 18 days
Aggregate Intrinsic Value
Intrinsic value on outstanding shares	$ 2,682
Intrinsic value on exercisable shares	$ 2,283
Other stock-based compensation
Fair value granted (in dollars per share)	$ 40.92	$ 32.33	$ 26.37
Total intrinsic value	$ 100	$ 4,600	$ 2,800
Unrecognized compensation expense	$ 2,400
Weighted-average recognition period	1 year 9 months 18 days
Restricted stock
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	96,047
Granted (in shares)	26,104
Vested (in shares)	(25,621)
Outstanding at the end of the period (in shares)	96,530	96,047
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 90.40
Granted (in dollars per share)	138.67
Vested (in dollars per share)	80.85
Non-vested at the end of the period (in dollars per share)	$ 105.99	$ 90.40
Other stock-based compensation
Unrecognized compensation expense	$ 4,100
Weighted-average recognition period	3 years 2 months 12 days
Restricted stock | Officers and Certain Employees
Non-vested other than stock options, number of shares
Granted (in shares)	19,630
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)	6,744
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)	144,912
Granted (in shares)	35,380
Vested (in shares)	(4,850)
Non-attainment (in shares)	(21,040)
Outstanding at the end of the period (in shares)	154,402	144,912
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 80.59
Granted (in dollars per share)	111.07
Vested (in dollars per share)	74.97
Non-attainment (in dollars per share)	71.44
Non-vested at the end of the period (in dollars per share)	$ 88.99	$ 80.59
Other stock-based compensation
Unrecognized compensation expense	$ 2,100
Weighted-average recognition period	2 years 1 month 6 days
Continuous service period for awards to vest	3 years
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)	$ 82.30
Contractual term of awards	3 years
Continuous service period for awards to vest	3 years