Segment Information (Narrative) (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) segments	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
REVENUES	$ 348,183	$ 203,040
Deferred Revenue, Revenue Recognized	2,700	5,900
Deferred Revenue	$ 1,800			$ 3,100
Number of reportable segments (in segments) | segments	2
Interest expense	$ 17,390	5,362
Customer Revenues [Member]
Segment Reporting Information [Line Items]
REVENUES	348,183	203,040
ACMI Services [Member]
Segment Reporting Information [Line Items]
REVENUES	257,956	119,374
Interest expense	6,500	500
ACMI Services [Member] | Customer Revenues [Member]
Segment Reporting Information [Line Items]
REVENUES		119,374
CAM [Member]
Segment Reporting Information [Line Items]
REVENUES	70,350	52,376
Interest expense	10,000	4,500
CAM [Member] | Customer Revenues [Member]
Segment Reporting Information [Line Items]
REVENUES		35,887
Ground Services [Member] | Customer Revenues [Member]
Segment Reporting Information [Line Items]
REVENUES	13,938		$ 16,154
MRO Services [Member] [Member] | Customer Revenues [Member]
Segment Reporting Information [Line Items]
REVENUES	33,981	$ 30,939
Flight Equipment [Member]
Segment Reporting Information [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	124,158			142,319
Operating Leases, Future Minimum Payments Receivable, in Two Years	156,008			127,097
Operating Leases, Future Minimum Payments Receivable, in Three Years	150,153			124,267
Operating Leases, Future Minimum Payments Receivable, in Four Years	124,667			121,226
Operating Leases, Future Minimum Payments Receivable, in Five Years	84,843			87,098
Operating Leases, Future Minimum Payments Receivable, Thereafter	$ 121,467			$ 119,761