CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 28,035,944	$ 45,533,443
Short-term investments	145,317,084	79,536,211
Receivables	0	706,403
Prepaid expenses	1,055,789	609,771
Other assets	636,058	652,510
Total current assets	175,044,875	127,038,338
Long-term investments	15,220,480	81,761,177
Property and equipment, net	3,672,433	3,970,665
Other noncurrent assets	31,194	31,194
Total assets	193,968,982	212,801,374
Current liabilities:
Accounts payable	1,541,162	1,234,759
Accrued wages and benefits	1,735,050	2,567,924
Accrued clinical trial expenses	1,509,430	2,336,645
Accrued expenses and other liabilities	675,491	745,668
Total current liabilities	5,461,133	6,884,996
Other liabilities, net of current portion	25,204	30,316
Deferred revenue, net of current portion	856,945	881,944
Total liabilities	6,343,282	7,797,256
Stockholders' equity:
Common stock: $0.001 par value, 100,000,000 shares authorized; 41,784,692 and 41,973,264 shares issued and outstanding at December 31, 2014 and June 30, 2015	41,973	41,785
Additional paid-in capital	377,551,054	373,571,500
Accumulated other comprehensive income	(28,141)	(143,928)
Retained deficit	(189,939,186)	(168,465,239)
Total stockholders' equity	187,625,700	205,004,118
Total liabilities and stockholders' equity	$ 193,968,982	$ 212,801,374