Cash, Cash Equivalents, and Investments - Summary of Amortized Cost and Fair Value of Short-term and Long-term Investments (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Due in less than one year	$ 10,733,249	$ 1,680,958
Due after one year, through two years	1,875,723
Amortized Cost [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Due in less than one year	10,733,249
Due after one year, through two years	1,875,723
Total short-term and long-term investments	12,608,972
Fair Value [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Due in less than one year	10,740,229
Due after one year, through two years	1,876,217
Total short-term and long-term investments	$ 12,616,446