Business Segments and Geographic Areas - Summary of Gains on Disposition of Property and Equipment and Other Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	$ 157,705	$ 102,590	$ 136,419
Depreciation and amortization	50,848	42,848	41,495
Total assets	1,376,080	1,173,323
Oil and Gas [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	119,235	62,934	115,543
Depreciation and amortization	29,635	26,653	24,048
Total assets	726,008	643,384
Air Medical [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	37,317	37,728	19,516
Depreciation and amortization	13,067	11,395	10,208
Total assets	336,510	318,345
Technical Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Depreciation and amortization	493	172	83
Total assets	7,842	8,686
Corporate [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Expenditures for long-lived assets	1,153	1,928	1,360
Depreciation and amortization	7,653	4,628	7,156
Total assets	$ 305,720	$ 202,908