Cash and Cash Equivalents - Cash and Cash Equivalents (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Cash And Cash Equivalents [Abstract]
Cash	$ 81,242	$ 209,380
Money market fund	22,151,106	12,615,710
Total cash and cash equivalents	$ 22,232,348	$ 12,825,090	$ 18,036,626	$ 4,363,712