Segment Information - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018 States Aircraft Location Segment	Jun. 30, 2017
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			3
National Science Foundation [Member]
Segment Reporting Information [Line Items]
Number of aircraft assigned			6
Hospitals Contracts [Member]
Segment Reporting Information [Line Items]
Segment revenue	16.00%	18.00%	18.00%	18.00%
Fixed Term Customer Contract [Member]
Segment Reporting Information [Line Items]
Segment revenue	87.00%	88.00%	87.00%	88.00%
Contracted Customers [Member]
Segment Reporting Information [Line Items]
Segment revenue			13.00%	12.00%
Minimum [Member]
Segment Reporting Information [Line Items]
Term of contract			1 year
Maximum [Member]
Segment Reporting Information [Line Items]
Term of contract			7 years
Oil and Gas [Member]
Segment Reporting Information [Line Items]
Number of aircraft available for use			125
Segment revenue	57.00%	51.00%	58.00%	52.00%
Oil and Gas [Member] | Minimum [Member] | Major Customer [Member]
Segment Reporting Information [Line Items]
Working period with major customers			35 years
Oil and Gas [Member] | Minimum [Member] | ENI Petroleum [Member]
Segment Reporting Information [Line Items]
Working period with major customers			20 years
Air Medical [Member]
Segment Reporting Information [Line Items]
Segment revenue	40.00%	46.00%	38.00%	44.00%
Number of aircraft assigned			109
Number of states in which company operates aircrafts | States			18
Locations in which company operates Aircrafts | Location			74
Technical Services [Member]
Segment Reporting Information [Line Items]
Segment revenue	3.00%	3.00%	4.00%	4.00%