Asset Retirement Obligations (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
asset retirement obligations [Line Items]
Surety bonds outstanding	$ 26,000
Letters of credit outstanding	20,000
Cash collateral for surety bond	600
Sinking fund for asset retirement obligations	20,000
Asset retirement obligations
asset retirement obligations [Line Items]
Surety bonds outstanding	$ 500,500