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Stock-Based Compensation - Restricted Stock Units and Restricted Stock Activity (Detail) - 2007 Plan [Member]
3 Months Ended
Mar. 31, 2021
$ / shares
shares
Restricted Stock Units (RSUs) [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unvested Shares, Beginning Balance | shares 453,501
Granted, Shares | shares 135,039
Vested, Shares | shares (173,372)
Forfeited, Shares | shares
Unvested Shares, Ending Balance | shares 415,168
Unvested, Weighted-Average Grant-Date Fair Value, Beginning Balance | $ / shares $ 4.11
Granted, Weighted-Average Grant-Date Fair Value | $ / shares 2.72
Vested, Weighted-Average Grant-Date Fair Value | $ / shares 2.82
Forfeited, Weighted-Average Grant-Date Fair Value | $ / shares
Unvested, Weighted-Average Grant-Date Fair Value, Ending Balance | $ / shares $ 3.79
Restricted Stock [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unvested Shares, Beginning Balance | shares 12,500
Vested, Shares | shares 0
Forfeited, Shares | shares 0
Unvested Shares, Ending Balance | shares 12,500
Unvested, Weighted-Average Grant-Date Fair Value, Beginning Balance | $ / shares $ 4.84
Vested, Weighted-Average Grant-Date Fair Value | $ / shares 0
Forfeited, Weighted-Average Grant-Date Fair Value | $ / shares 0
Unvested, Weighted-Average Grant-Date Fair Value, Ending Balance | $ / shares $ 4.84