Fair Value Measurement - Statement Of Income Classification (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Fair Value Statement Of Income Classification [Line Items]
Realized/unrealized derivative gain (loss), net			$ (100)		$ 200
Sales
Fair Value Statement Of Income Classification [Line Items]
Realized/unrealized derivative gain (loss), net	$ 206	$ (472)	(532)	$ 1,365
Other Operating Income (Expense)
Fair Value Statement Of Income Classification [Line Items]
Realized/unrealized gold and silver rounds/bullion gain, net	$ 608	$ 224	$ 456	$ 239