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, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	$ 82,871	$ 56,575	$ 157,705
Depreciation and amortization	65,743	71,618	50,848
Total assets	1,448,440	1,426,333
Reportable Operating Segments [Member] | Oil and Gas [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	59,278	32,501	119,235
Depreciation and amortization	40,170	42,709	29,635
Total assets	674,788	704,472
Reportable Operating Segments [Member] | Air Medical [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	22,429	22,685	37,317
Depreciation and amortization	19,716	18,177	13,067
Total assets	368,474	329,484
Reportable Operating Segments [Member] | Technical Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and amortization	564	518	493
Total assets	9,568	7,345
Corporate [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	1,164	1,389	1,153
Depreciation and amortization	5,293	10,214	$ 7,653
Total assets	$ 395,610	$ 385,032