Summary of Significant Accounting Policies - Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Other Current Liabilities:
Accrued interest payable	$ 91,953	$ 36,590
Current portion of long-term capacity contracts	50,504	34,000
Taxes other than income	44,619	57,850
Incentive compensation	33,601	18,573
Current portion of operating lease liabilities	25,004	29,036
Income tax payable	23,909	0
Severance accrual	2,536	11,769
Other accrued liabilities	29,785	32,746
Other current liabilities	$ 301,911	$ 220,564