Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents maturity period less than (in days)	P90D
Short-term investments maturity period less than (in years)	P1Y
Aggregate capital leased assets, gross	$ 760.4	$ 715.3
Accumulated depreciation on capital leases	$ 199.2	$ 161.4
Minimum
Cash and Cash Equivalents [Line Items]
Long-term investments maturity period (in years)	P1Y
Maximum
Cash and Cash Equivalents [Line Items]
Long-term investments maturity period (in years)	P3Y