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Stock-Based Compensation - Assumptions Used to Compute Share-Based Compensation Costs for Stock Options Granted (Detail) - $ / shares
6 Months Ended 12 Months Ended
Sep. 30, 2019
Mar. 31, 2019
Sep. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]            
Weighted average grant date fair value of stock options         $ 1.84 $ 1.56
Assumptions            
Risk-free interest rate (weighted average) 1.84% 2.44% 2.29% 1.92% 2.36% 2.90%
Weighted average expected life (years) 6 months 6 months 6 months 6 months 6 years 2 months 12 days 6 years 2 months 12 days
Volatility (weighted average) 86.30% 51.70% 54.30% 81.40% 78.70% 73.80%
Forfeiture rate         26.00% 26.60%