Business Segments and Geographic Areas - Summary of Gains on Disposition of Property and Equipment and Other Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	$ 42,908	$ 58,478	$ 82,871
Depreciation and amortization	79,254	68,027	65,743
Total assets	1,262,226	1,401,846
Reportable Operating Segments [Member] | Oil and Gas [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	34,171	52,525	59,278
Depreciation and amortization	47,723	39,655	40,170
Total assets	594,331	722,734
Reportable Operating Segments [Member] | Air Medical [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	7,268	5,696	22,429
Depreciation and amortization	22,606	20,413	19,716
Total assets	387,701	372,646
Reportable Operating Segments [Member] | Technical Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and amortization	499	581	564
Total assets	5,515	5,979
Corporate [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	1,469	257	1,164
Depreciation and amortization	8,426	7,378	$ 5,293
Total assets	$ 274,679	$ 300,487