Valuation Accounts - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	$ 6.8		$ 6.8		$ 7.2
Value of services to patients who are unable to pay	2.2	$ 1.3	7.1	$ 5.7
Estimated cost of providing charity services	0.5	$ 0.3	1.7	$ 1.3
Valuation reserves related to obsolescence and slow moving inventory	23.1		23.1		20.9
Air Medical [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for contractual discounts against outstanding accounts receivable	119.9		119.9		117.8
Allowance for uncompensated care against outstanding accounts receivable	$ 64.7		$ 64.7		$ 52.5