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Stock-Based Compensation - Additional Information (Detail) (USD $)
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3 Months Ended | 3 Months Ended | 3 Months Ended | |||||||||
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Mar. 31, 2012
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Mar. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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Mar. 31, 2013
Nineteen Ninety Four Plan
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Dec. 31, 2004
Nineteen Ninety Four Plan
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Mar. 31, 2013
Two Thousand Three Plan
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Sep. 18, 2003
Two Thousand Three Plan
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Dec. 31, 2010
Amended Two Thousand Three Plan
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Dec. 31, 2008
Amended Two Thousand Three Plan
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Dec. 31, 2007
Amended Two Thousand Three Plan
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Mar. 31, 2013
Restricted Stock
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||||||
| Common stock reserved for future issuance | 450,000 | 450,000 | 1,160,000 | 810,000 | 670,000 | 1,041,000 | ||||||
| Shares of common stock vested and exercisable | 12,000 | 680,868 | ||||||||||
| Percentage of option price | 100.00% | 100.00% | ||||||||||
| Stock option period | 10 years | 10 years | ||||||||||
| Common stock vesting period | 3 years | 3 years | ||||||||||
| Weighted average fair value of options granted at market | $ 0.49 | |||||||||||
| Shares available to issued under stock incentive plan | 391,337 | 381,170 | 353,953 | 959,000 |