Valuation Accounts - Schedule of Allowance for Contractual Discounts and Estimated Uncompensated Care as a Percentage of Gross Segment Accounts Receivable (Detail) - Air Medical [Member] - Trade Accounts Receivable [Member]	Sep. 30, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Contractual Discounts	48.00%	53.00%
Allowance for Uncompensated Care	26.00%	24.00%