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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2013 | Sep. 30, 2012 | Sep. 30, 2013 | Sep. 30, 2012
Property, Plant and Equipment [Line Items] |  |  |  |
Number of shares sold |  |  | 23,000,000 |
Proceeds from sale of subsidiary stock |  |  | $ 25,000,000 |
Ratio of remaining net proceed |  |  | 0.25 |
Short-term investment maturity period |  |  | Three months or less |
Securities owned | $ 0 |  | $ 0 |
Weighted average number of common shares outstanding | 80,252,203 | 81,440,848 | 78,991,192 | 73,498,034
Minimum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Property and Equipment, estimated useful life |  |  | 3 years |
Maximum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Property and Equipment, estimated useful life |  |  | 10 years |

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