Additional Balance Sheet Detail and Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Other Liabilities Disclosure [Abstract]
Other Accrued Liabilities		$ 3,327	$ 3,752
Unrealized Gain (Loss) on Derivatives		24,950	411
Accrued Income Taxes, Current		26,118	11,243
Accrual for Taxes Other than Income Taxes, Current		3,616	3,554
Interest Payable, Current		1,855	1,833
Accrued Salaries, Current		30,457	20,047
Silvertip acquisition contingent consideration		0	25,000
Deferred Revenue	[1]	16,425	16,672
Accrued liabilities and other		$ 119,158	$ 95,616

[1] (1) See Note 21 -- Commitments and Contingencies for additional details on deferred revenue liabilities