Business Segments and Geographic Areas - Schedule of Accounts Receivable and Revenue by Major Customers by Reporting Segments (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Customer Concentration Risk [Member] | Oil and Gas [Member] | Sales Revenue, Segment [Member] | Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration risk, percentage	14.00%	15.00%	17.00%
Customer Concentration Risk [Member] | Oil and Gas [Member] | Sales Revenue, Segment [Member] | Customer B [Member]
Revenue, Major Customer [Line Items]
Concentration risk, percentage	10.00%	11.00%	13.00%
Customer Concentration Risk [Member] | Air Medical and Technical Services [Member] | Sales Revenue, Segment [Member] | Customer C [Member]
Revenue, Major Customer [Line Items]
Concentration risk, percentage	5.00%	9.00%	10.00%
Concentration of Credit Risk [Member] | Oil and Gas [Member] | Accounts Receivable [Member] | Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration risk, percentage	8.00%	6.00%
Concentration of Credit Risk [Member] | Oil and Gas [Member] | Accounts Receivable [Member] | Customer B [Member]
Revenue, Major Customer [Line Items]
Concentration risk, percentage	8.00%	9.00%
Concentration of Credit Risk [Member] | Air Medical and Technical Services [Member] | Accounts Receivable [Member] | Customer C [Member]
Revenue, Major Customer [Line Items]
Concentration risk, percentage	13.00%	15.00%