Basis of Presentation - Disaggregated Revenue by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Operating revenues, net	$ 168,787	$ 150,167	$ 498,400	$ 431,209
Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	168,787	150,167	498,400	431,209
Oil and Gas [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	93,338	75,700	286,046	222,098
Air Medical [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	70,192	70,280	194,331	192,840
Technical Services [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	5,257	4,187	18,023	16,271
Traditional Provider Model [Member] | Air Medical [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	12,414	11,816	36,371	35,427
Independent Provider Model [Member] | Air Medical [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	$ 57,778	$ 58,464	$ 157,960	$ 157,413