Cash, Cash Equivalents, and Investments - Summarized Classification of Short Term and Long Term Investments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Investments Schedule [Abstract]
Cash	$ 32,051,501	$ 19,811,735
Cash equivalents	2,953,993	16,315,056
Total cash and cash equivalents	35,005,494	36,126,791	25,965,711	21,300,733
Short-term investments	8,751,409	1,680,958
Long-term investments	4,580,049
Total cash, cash equivalents and investments	$ 48,336,952	$ 37,807,749