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Stock-Based Compensation - Restricted Stock Units and Restricted Stock Activity (Detail) - 2007 Plan [Member] - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Restricted Stock Units (RSUs) [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unvested Shares, Beginning Balance 476,667 429,833
Granted, Shares 206,750 343,518
Vested, Shares (130,333) (201,300)
Forfeited, Shares (99,583) (95,384)
Unvested Shares, Ending Balance 453,501 476,667
Unvested, Weighted-Average Grant-Date Fair Value, Beginning Balance $ 4.94 $ 9.77
Granted, Weighted-Average Grant-Date Fair Value 2.99 3.49
Vested, Weighted-Average Grant-Date Fair Value 5.48 9.03
Forfeited, Weighted-Average Grant-Date Fair Value 3.22 4.50
Unvested, Weighted-Average Grant-Date Fair Value, Ending Balance $ 4.11 $ 4.94
Restricted Stock [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unvested Shares, Beginning Balance 32,000 101,500
Vested, Shares (14,500) (54,000)
Forfeited, Shares (5,000) (15,500)
Unvested Shares, Ending Balance 12,500 32,000
Unvested, Weighted-Average Grant-Date Fair Value, Beginning Balance $ 5.01 $ 6.42
Vested, Weighted-Average Grant-Date Fair Value 5.14 5.11
Forfeited, Weighted-Average Grant-Date Fair Value 4.65 4.07
Unvested, Weighted-Average Grant-Date Fair Value, Ending Balance $ 4.84 $ 5.01