Fair Value Accounting (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Accounting
Other investments, at fair value	$ 295	$ 3,676
Fair Value Transfers Between Levels	0
Recurring | Midas Gold Shares [Member]
Fair Value Accounting
Other investments, at fair value	295	3,676
Recurring | Fair Value, Inputs, Level 1 [Member] | Midas Gold Shares [Member]
Fair Value Accounting
Other investments, at fair value	295	3,676
Recurring | Fair Value, Inputs, Level 3 [Member] | Midas Gold Shares [Member]
Fair Value Accounting
Other investments, at fair value	$ 0	$ 0