Net Earnings (Loss) Per Share (Narrative) (Details) - shares	3 Months Ended	4 Months Ended	5 Months Ended	9 Months Ended
	Sep. 30, 2021	Apr. 30, 2021	Sep. 30, 2021	Sep. 30, 2021
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares included in the computation of diluted earnings per share (in shares)	1,264,000		1,198,000
Successor [Member] | Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares included in the computation of diluted earnings per share (in shares)				0
Predecessor [Member] | Old Frontier Director And Employee Compensation Plans [Member] | Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares included in the computation of diluted earnings per share (in shares)		339,544