Property and Equipment - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 20.3	$ 16.2	$ 11.2
Amortization expense of capitalized internal-use software	7.7	7.4	$ 6.2
Carrying value of capitalized internal-use software	17.7	15.4
Capitalized internal-use software included in construction in progress	$ 8.7	$ 5.4