Valuation Accounts - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	$ 7.3		$ 7.3		$ 7.2
Value of services to patients who are unable to pay	1.7	$ 2.0	3.3	$ 4.4
Estimated cost of providing charity services	0.4	$ 0.4	0.8	$ 1.0
Valuation reserves related to obsolescence and slow moving inventory	22.7		22.7		20.9
Air Medical [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for contractual discounts against outstanding accounts receivable	118.4		118.4		117.8
Allowance for uncompensated care against outstanding accounts receivable	$ 59.6		$ 59.6		$ 52.5