Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Adjustment of Warrants	$ (44,700)	$ (53,400)	$ (109,700)	$ 107,000	$ (72,900)	$ 92,000	$ (35,900)	$ 4,500	$ (95,500)	$ (2,300)	$ 7,400
Deferred Federal Income Tax Expense (Benefit)									19,701	14,155	15,642
Asset Impairment Charges		(39,100)							39,075	0	0
Income Tax (Expense) Benefit, Continuing Operations, Government Grants	15,700	21,700	9,800						47,231	0	0
REVENUES	399,358	404,146	377,794	389,277	403,351	366,073	334,576	348,183	1,570,575	1,452,183	892,345
Income (Loss) from Continuing Operations before Interest Expense, Interest Income, Income Taxes, Extraordinary Items, Noncontrolling Interests, Net	59,435	73,970	23,178	49,807	52,221	40,766	37,482	46,528
Net earnings from continuing operations	2,253	(5,745)	(105,162)	133,733	(41,104)	105,085	(26,632)	22,634	25,079	59,983	67,883
EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAXES	$ 2,874	$ 154	$ 236	$ 3,772	$ 914	$ 243	$ 31	$ 31	$ 7,036	$ 1,219	$ 1,402
Weighted average shares:
Basic (in shares)	59,195	59,146	59,130	59,040	58,929	58,919	58,909	58,838	59,128	58,899	58,765
Diluted (in shares)	70,074	59,146	59,130	67,947	58,929	68,718	58,909	60,437	59,931	69,348	68,356
Earnings (loss) per share from continuing operations
Basic (in dollars per share)	$ 0.04	$ (0.10)	$ (1.78)	$ 2.27	$ (0.70)	$ 1.78	$ (0.45)	$ 0.38	$ 0.42	$ 1.02	$ 1.16
Diluted (in dollars per share)	$ 0.03	$ (0.10)	$ (1.78)	$ 0.84	$ (0.70)	$ 0.19	$ (0.45)	$ 0.25	$ 0.42	$ 0.78	$ 0.89
Pension Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement									$ 424	$ 0	$ 0
ACMI Services [Member]
REVENUES									1,147,279	1,078,288	548,839
2017 Tax Cuts and Jobs Act [Member]
Deferred Federal Income Tax Expense (Benefit)									$ 0	$ 0	$ 0