Segment Information - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018 States Aircraft Location Segment	Sep. 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
Fixed Term Customer Contract [Member]
Segment Reporting Information [Line Items]
Segment revenue (percent)	85.00%	89.00%	87.00%	90.00%
Contracted Customers [Member]
Segment Reporting Information [Line Items]
Segment revenue (percent)			13.00%	10.00%
Hospitals Contracts [Member]
Segment Reporting Information [Line Items]
Segment revenue (percent)	17.00%	15.00%	17.00%	17.00%
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			126
Segment revenue (percent)	55.00%	50.00%	57.00%	51.00%
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 (percent)	42.00%	47.00%	39.00%	45.00%
Number of aircraft assigned			108
Number of states in which company operates aircrafts | States			18
Locations in which company operates Aircrafts | Location			80
Technical Services [Member]
Segment Reporting Information [Line Items]
Segment revenue (percent)	3.00%	3.00%	4.00%	4.00%