Summary of Significant Accounting Policies (Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset commodity		$ 636
Assets		636
SARs liability	$ 2,289	2,638
SARs liability	193	852
Liabilities	2,482	3,490
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset commodity		636
Assets		636
SARs liability	2,289	2,638
SARs liability	193	852
Liabilities	$ 2,482	$ 3,490