Other Assets Noncurrent(Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Prepaid Expense and Other Assets [Abstract]
Lessor, Operating Lease, Payments to be Received	$ 27,043	$ 28,948
Spare parts	26,486	22,725
Equity Method Investments	3,250	0
Finance Lease, Right-of-Use Asset	2,690	2,915
Other Assets, Miscellaneous, Noncurrent	1,330	887
OTHER ASSETS	$ 60,799	$ 55,475	[1]

[1] December 31, 2020 balances were derived from audited consolidated financial statements.