STOCK-BASED COMPENSATION - NON-OPTIONS (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2021	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 (SARs)
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	184,137
Granted (in shares)	0
Exercised (in shares)	0
Outstanding at the end of the period (in shares)	184,137	184,137
Exercisable at the end of the period (in shares)	123,976
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 111.15
Non-vested at the end of the period (in dollars per share)	111.15	$ 111.15
Exercisable at the end of the period (in dollars per share)	$ 99.81
Other than stock options, weighted-average remaining contractual life (in years)
Outstanding at the end of the period	7 years 2 months 12 days
Exercisable at the end of the period	6 years 7 months 6 days
Aggregate Intrinsic Value
Intrinsic value on outstanding shares	$ 2,049
Intrinsic value on exercisable shares	$ 2,025
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
Restricted Stock
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	96,530
Granted (in shares)	50,604
Vested (in shares)	(19,076)
Outstanding at the end of the period (in shares)	128,058	96,530
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 105.99
Granted (in dollars per share)	111.28
Vested (in dollars per share)	86.16
Non-vested at the end of the period (in dollars per share)	$ 111.03	$ 105.99
Restricted Stock | Officers and Certain Employees [Member]
Non-vested other than stock options, number of shares
Granted (in shares)	42,810
Other stock-based compensation
Vesting period	3 years	3 years	3 years	3 years
Holding period of awards as a vesting condition		2 years	2 years	2 years
Vesting (as a percent)		33.00%	33.00%	33.00%
Restricted Stock | Non Executive Directors [Member]
Non-vested other than stock options, number of shares
Granted (in shares)	7,794
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 Shares
Non-vested other than stock options, number of shares
Outstanding at the beginning of the period (in shares)	154,402
Granted (in shares)	73,200
Vested (in shares)	(3,070)
Non-attainment (in shares)	(57,154)
Outstanding at the end of the period (in shares)	167,378	154,402
Other than stock options, weighted-average grant date fair value
Non-vested at the beginning of the period (in dollars per share)	$ 88.99
Granted (in dollars per share)	123.35
Vested (in dollars per share)	122.27
Non-attainment (in dollars per share)	77.73
Non-vested at the end of the period (in dollars per share)	$ 108.75	$ 88.99
Other stock-based compensation
Earn out basis if no goals are met (as a percent)		0.00%	0.00%	0.00%
Earn out basis if some goals are met (as a percent)		100.00%	100.00%	100.00%
Earn out basis if all goals are met (as a percent)	200.00%	200.00%	200.00%	200.00%
Performance Shares | Vesting upon achievement of annual growth in Net GEOs
Other stock-based compensation
Vesting (as a percent)		50.00%	50.00%	50.00%
Gold Equivalent Ounces Shares
Other stock-based compensation
Contractual term of awards		5 years	5 years	5 years
Total Shareholder Return Shares
Other stock-based compensation
Contractual term of awards	3 years	3 years	3 years	3 years
Continuous service period for awards to vest	3 years	3 years	3 years	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%