Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Additional Information (Detail)

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Stock Based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Stock-based compensation expense $ 922,000 $ 25,000 $ 1,565,000 $ 52,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the equity incentive plans 16,000,000   $ 16,000,000  
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the equity incentive plans, period for recognition     3 years 4 months 24 days  
Total intrinsic value of stock options exercised 30,000   $ 1,600,000  
Cash received from stock option exercises $ 8,000 $ 0 156,000 $ 0
Tax benefit realized upon exercise of option     $ 0