Equity and Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Proceeds from common stock issuance, net	$ 1,400.0			$ 1,399.0
Stock-based compensation expense		$ 45.0	$ 10.4	$ 57.7	$ 21.3
DST [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense		33.3
One-time charges for accelerated vesting awards		$ 28.1
Common Stock [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Common stock shares issued	30,262,250
Common stock offering price to public	$ 47.50
Common Stock [Member] | Underwriters' Option [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Common stock shares issued	3,947,250