Stock-Based Compensation Expense - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Grants in period, net of forfeitures		70,000	0	84,000
Grants in period, estimated fair value (usd per share)		$ 4.62	$ 15.87	$ 8.57
Total intrinsic value of options exercised		$ 3.6	$ 5.5	$ 9.3
Unrecognized stock-based compensation balance after estimated forfeitures related to unvested stock options	$ 2.2	$ 0.7	$ 2.2
Estimated weighted average amortization period		2 years 4 months 24 days	2 years 5 months
Issuance of common stock in connection with employee common stock purchase plan (in shares)		164,000	89,000	77,000
Stock-based compensation expense, incremental compensation cost				$ 0.3
Black Scholes Option Pricing Model
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Expected life (in years)		2 years
Restricted Stock Awards And Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Restricted stock awards, total fair value		$ 22.7	$ 15.9	$ 7.7
Unrecognized stock-based compensation balance after estimated forfeitures related to unvested stock options	$ 33.7	$ 48.8	$ 33.7
Estimated weighted average amortization period		1 year 9 months 18 days	1 year 2 months 6 days
DTS Merger
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Shares assumed and granted in connection with acquisition	682,000