Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Adjustment of Warrants	$ 20,400	$ (34,400)	$ (67,600)	$ 1,900	$ (14,700)	$ (8,500)	$ 5,600	$ (500)	$ (81,800)
Deferred Federal Income Tax Expense (Benefit)									27,625	$ 11,338	$ 21,073
REVENUES	322,971	254,101	253,211	237,917	221,675	193,261	176,549	177,385	1,068,200	768,870	619,264
Income (Loss) from Continuing Operations before Interest Expense, Interest Income, Income Taxes, Extraordinary Items, Noncontrolling Interests, Net	33,671	18,923	22,948	17,753	18,140	14,456	15,801	15,351
Net earnings (loss) from continuing operations	94,091	(28,229)	(53,918)	9,796	(755)	2,116	11,528	8,171	21,740	21,060	39,155
EARNINGS (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAXES	$ 1,026	$ (4,655)	$ 192	$ 192	$ 2,287	$ 47	$ 47	$ 47	$ (3,245)	$ 2,428	$ 2,067
Weighted average shares:
Basic (in shares)	58,733	58,733	59,035	59,133	59,083	59,379	63,267	63,636	58,907	61,330	64,242
Diluted (in shares)	68,987	58,733	59,035	64,949	59,083	60,283	66,763	65,057	59,686	62,994	65,127
Earnings per share from continuing operations
Basic (in dollars per share)	$ 1.60	$ (0.48)	$ (0.91)	$ 0.17	$ (0.01)	$ 0.04	$ 0.18	$ 0.13	$ 0.37	$ 0.34	$ 0.61
Diluted (in dollars per share)	$ 1.11	$ (0.48)	$ (0.91)	$ 0.13	$ (0.01)	$ 0.04	$ 0.12	$ 0.13	$ 0.36	$ 0.33	$ 0.60
Pension Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement									$ (12,923)	$ 0	$ 0
Pension Plans [Member] | Continuing Operations [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement									5,300
Pension Plans [Member] | Discontinued Operations [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement									7,600
ACMI Services [Member]
REVENUES									614,741	492,859	433,109
2017 Tax Cuts and Jobs Act [Member]
Deferred Federal Income Tax Expense (Benefit)					$ 59,900				$ (59,944)	$ 0	$ 0