Segment Information - Depreciation and Amortization Expense Included in Direct Expenses and Unallocated Selling, General, and Administrative Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reportable Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and Amortization Expenses	$ 16,024	$ 15,424	$ 45,638	$ 46,135
Reportable Operating Segments [Member] | Oil and Gas [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and Amortization Expenses	10,616	11,194	30,558	32,797
Reportable Operating Segments [Member] | Air Medical [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and Amortization Expenses	5,267	4,100	14,654	12,948
Reportable Operating Segments [Member] | Technical Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and Amortization Expenses	141	130	426	390
Unallocated Selling, General and Administrative Expenses [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and Amortization Expenses	$ 2,269	$ 2,376	$ 7,416	$ 8,177