Equity Incentive Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
	Oct. 31, 2017	May 02, 2017	Feb. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period (in years)				10 years
Options granted during the period (in shares)				3,126,698
Common stock issued through stock grants				130,426	133,717	158,014
Options issued (in shares)		6,930			7,550
Options issued (in usd per share)		$ 81.15		$ 11.00	$ 10.70
Common stock issued through exercise of options (in shares)				220,000	440,000	220,000
Exercises in period, intrinsic value				$ 13.9	$ 18.3
Intrinsic value of outstanding and exercisable options				14.5	$ 22.0	$ 37.7
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued through stock grants					133,717	158,014
Share based compensation expense to be recognized				4.4
Share based compensation expense, restricted stock grant				$ 9.4	$ 9.2	$ 8.6
Period for recognition of cost not recognized (in years)				1 year 1 month 6 days
Management | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued through stock grants	188	55,238	75,000		133,717	158,014
Share based compensation, fair market value	$ 0.0	$ 4.5	$ 5.4		$ 9.1	$ 8.6
Options issued (in shares)					7,550
Options issued (in usd per share)					$ 74.53
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum shares of common stock available for grant (in shares)				3,750,000
Vests on May 8, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights (in percentage)				33.33%
Vests on November 8, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights (in percentage)				33.33%
Vests on May 8, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights (in percentage)				33.33%