Summary of Significant Accounting Policies - Schedule of Net Revenue Attributable to Medicaid, Medicare, Private Insurance and Self Pay as Percentage of Net Air Medical Independent Provider Model Revenues (Detail) - Air Medical [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance [Member]
Segment Reporting Information [Line Items]
Percentage of net Air Medical revenues	72.00%	72.00%	74.00%
Medicare [Member]
Segment Reporting Information [Line Items]
Percentage of net Air Medical revenues	18.00%	18.00%	17.00%
Medicaid [Member]
Segment Reporting Information [Line Items]
Percentage of net Air Medical revenues	9.00%	9.00%	8.00%
Self Pay [Member]
Segment Reporting Information [Line Items]
Percentage of net Air Medical revenues	1.00%	1.00%	1.00%