Revenue Recognition and Valuation Accounts - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	$ 6.1		$ 6.1		$ 6.0
Value of services to patients who are unable to pay	1.3	$ 2.2	5.7	$ 6.9
Estimated cost of providing charity services	0.3	$ 0.5	1.3	$ 1.8
Valuation reserves related to obsolescence and slow moving inventory	18.4		18.4		17.3
Air Medical [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for contractual discounts against outstanding accounts receivable	129.2		129.2		111.9
Allowance for uncompensated care against outstanding accounts receivable	$ 47.7		$ 47.7		$ 46.3