Asset Retirement Obligations (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
asset retirement obligations [Line Items]
Surety bonds outstanding	$ 552,500
Cash collateral for surety bond	5,600
Sinking fund for asset retirement obligations	6,273	$ 115,993	$ 20,000
Asset retirement obligations
asset retirement obligations [Line Items]
Surety bonds outstanding	455,700
Cash collateral for surety bond	600
Sinking fund for asset retirement obligations	$ 142,300