Fair Value Accounting (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Accounting
Other investments, at fair value	$ 2,247	$ 3,676
Fair Value Transfers Between Levels	0
Recurring | Midas Gold Shares [Member]
Fair Value Accounting
Other investments, at fair value	2,247	3,676
Recurring | Fair Value, Inputs, Level 1 [Member] | Midas Gold Shares [Member]
Fair Value Accounting
Other investments, at fair value	$ 2,247	$ 3,676