Cash, Cash Equivalents, and Investments - Summary of Amortized Cost and Fair Value of Short-term and Long-term Investments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	$ 8,751,409	$ 1,680,958
Due after one year, through two years	4,580,049
Amortized Cost [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	8,751,409
Due after one year, through two years	4,580,049
Total short-term and long-term investments	13,331,458
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	8,756,782
Due after one year, through two years	4,573,855
Total short-term and long-term investments	$ 13,330,637