Other Income (Loss), Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Anthem
Schedule of Other Nonoperating Income Expense [Line Items]
Gain from cost method investment	$ 4.8
Proceeds from sales / distributions of ownership interests			$ 1.0
iNovate
Schedule of Other Nonoperating Income Expense [Line Items]
Gain from cost method investment	$ 1.1
InstaMed
Schedule of Other Nonoperating Income Expense [Line Items]
Gain from cost method investment		$ 2.8
Acquirgy
Schedule of Other Nonoperating Income Expense [Line Items]
Loan repayment from equity / cost method investment			$ 0.4