Basis of Presentation - Disaggregated Revenue by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Operating revenues, net	$ 169,243	$ 146,424	$ 329,607	$ 281,042
Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	169,243	146,424	329,607	281,042
Oil and Gas [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	97,068	74,668	192,702	146,399
Air Medical [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	67,151	67,222	124,139	122,559
Technical Services [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	5,024	4,534	12,766	12,084
Traditional Provider Model [Member] | Air Medical [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	12,085	12,140	23,956	23,610
Independent Provider Model [Member] | Air Medical [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, net	$ 55,066	$ 55,082	$ 100,183	$ 98,949