Nature of Ops and Sign. Acctg Policies (Reconciliation of Weighted Average Shares Table) (Details 3) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 18, 2020		Dec. 31, 2019		Dec. 31, 2018
Numerator
Net income (loss) - basic	$ (50,658)	$ (1,432,578)		$ 216,959		$ 322,698
Interest on convertible senior notes including amortization of discount, net of tax	0	0		14,134		539
Net income (loss) - diluted	$ (50,658)	$ (1,432,578)		$ 231,093		$ 323,237
Denominator
Weighted average common shares outstanding – basic	50,000	495,560		459,524		432,483
Restricted stock and performance-based equity awards	0	0		2,396		6,500
Convertible senior notes	0	0	[1]	48,421	[1]	17,186	[1]
Weighted average common shares outstanding – diluted	50,000	495,560		510,341		456,169
Predecessor common shares issuable upon full conversion of convertible senior notes				90,900

[1] For the year ended December 31, 2019, shares shown under “convertible senior notes” represent the prorated portion of the approximately 90.9 million shares of the Predecessor’s common stock issuable upon full conversion of the convertible senior notes which were issued on June 19, 2019 (see Note 8, Long-Term Debt – 2019 Predecessor Debt Reduction Transactions).