Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 18, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Cash paid for interest, expensed	$ 813	$ 29,357	$ 72,842	$ 50,076
Cash paid for interest, capitalized	1,261	22,885	36,671	37,079
Cash paid for interest, treated as a reduction of debt	0	46,417	85,303	79,606
Cash paid for income taxes	0	453	2,361	492
Cash received from income tax refunds	10,457	1,932	9,820	8,280
Noncash investing and financing activities
Increase in asset retirement obligations	23,398	4,328	13,560	4,499
Increase (decrease) in liabilities for capital expenditures	1,867	(12,809)	(17,740)	14,600
Conversion of convertible senior notes into common stock	$ 0	$ 11,501	$ 0	$ 162,004