Consolidated Statements of Changes in Stockholder's Equity - USD ($) $ in Thousands	Common Shares	Additional Paid-In Capital	Accumulated (Losses) Earnings	Noncontrolling Interests	Total
Balance at Jun. 30, 2019	$ 655	$ 2,201,773	$ (65,747)	$ 33,772	$ 2,170,453
Balance (in shares) at Jun. 30, 2019	65,440,492
Increase (Decrease) in Stockholders' Equity
Stock-based compensation and related share issuances		891			891
Stock-based compensation and related share issuances (in shares)	55,512
Distributions from (to) non-controlling interests		2,700		(379)	2,321
Net income (loss) and comprehensive income (loss)			111,774	(2,488)	109,286
Dividends declared			(35,737)		(35,737)
Balance at Dec. 31, 2019	$ 655	2,205,364	10,290	30,905	2,247,214
Balance (in shares) at Dec. 31, 2019	65,496,004
Balance at Sep. 30, 2019	$ 655	2,202,350	(12,676)	31,999	2,222,328
Balance (in shares) at Sep. 30, 2019	65,495,787
Increase (Decrease) in Stockholders' Equity
Stock-based compensation and related share issuances		1,214			1,214
Stock-based compensation and related share issuances (in shares)	217
Distributions from (to) non-controlling interests		1,800		(187)	1,613
Net income (loss) and comprehensive income (loss)			41,321	(907)	40,414
Dividends declared			(18,355)		(18,355)
Balance at Dec. 31, 2019	$ 655	2,205,364	10,290	30,905	2,247,214
Balance (in shares) at Dec. 31, 2019	65,496,004
Balance at Jun. 30, 2020	$ 655	2,210,429	61,133	29,902	2,302,119
Balance (in shares) at Jun. 30, 2020	65,531,288
Increase (Decrease) in Stockholders' Equity
Stock-based compensation and related share issuances	$ 1	1,476			1,477
Stock-based compensation and related share issuances (in shares)	17,127
Sale of Peak Gold JV interest		(10,829)		(16,218)	(27,047)
Distributions to non-controlling interests				(481)	(481)
Net income (loss) and comprehensive income (loss)			166,828	(166)	166,662
Dividends declared			(38,051)		(38,051)
Balance at Dec. 31, 2020	$ 656	2,201,076	189,910	13,037	2,404,679
Balance (in shares) at Dec. 31, 2020	65,548,415
Balance at Sep. 30, 2020	$ 656	2,199,705	149,702	13,158	2,363,221
Balance (in shares) at Sep. 30, 2020	65,545,606
Increase (Decrease) in Stockholders' Equity
Stock-based compensation and related share issuances		1,371			1,371
Stock-based compensation and related share issuances (in shares)	2,809
Distributions to non-controlling interests				(220)	(220)
Net income (loss) and comprehensive income (loss)			59,889	99	59,988
Dividends declared			(19,681)		(19,681)
Balance at Dec. 31, 2020	$ 656	$ 2,201,076	$ 189,910	$ 13,037	$ 2,404,679
Balance (in shares) at Dec. 31, 2020	65,548,415