Fair Value Measurements (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Additions to asset retirement obligations	$ 294
Revisions to asset retirement obligations		361
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Additions to asset retirement obligations		$ 14,100
Revisions to asset retirement obligations	290,000
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Minimum [Member] | Abandonment Costs Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset retirement obligation liability	$ 20
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Minimum [Member] | Inflation rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset retirement obligation, measurement input rate	1.52%
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Minimum [Member] | Risk-free rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset retirement obligation, measurement input rate	3.28%
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Minimum [Member] | Reclamation Period [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated timing of reclamation range (in years)	1 year
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Maximum [Member] | Abandonment Costs Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset retirement obligation liability	$ 45
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Maximum [Member] | Inflation rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset retirement obligation, measurement input rate	2.79%
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Maximum [Member] | Risk-free rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset retirement obligation, measurement input rate	8.27%
Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member] | Maximum [Member] | Reclamation Period [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated timing of reclamation range (in years)	75 years
Class A Units [Member] | Subordinated Notes [Member] | Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of common units issued	1,425
Fair value of debt discount	$ 1,300
Fair value per Class A unit	$ 1,000
Class A Units [Member] | 2018 Subordinated Notes [Member] | Fair Value, Inputs, Level 3 [Member] | Non-Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of common units issued	585
Fair value of debt discount	$ 490