CONDENSED STATEMENTS OF CASH FLOWS - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities
Net income (loss)	$ (11,488,585)	$ (10,152,740)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	238,347	217,252
Stock-based compensation	1,132,519	2,084,198
Loss on disposal of property and equipment	2,222
Accretion of bond premium	43,001	195,962
Change in operating assets and liabilities:
Receivables	22,435	8,678
Prepaid expenses and other assets	396,962	(95,744)
Accounts payable	(3,085)	(546,342)
Accrued wages, benefits and other liabilities	(814,721)	(1,835,004)
Deferred revenue	(12,500)	(12,500)
Net cash used in operating activities	(10,483,405)	(10,136,240)
Investing activities
Purchases of property and equipment	(29,536)	(35,898)
Purchases of investments	(14,977,694)	(41,852,513)
Proceeds from sale and maturities of investments	28,000,000	76,765,000
Net cash provided by investing activities	12,992,770	34,876,589
Financing activities
Stock repurchase	(92,929)	(108,501)
Proceeds from the exercise of stock options	16,290	93,477
Net cash used in financing activities	(76,639)	(15,024)
Net increase (decrease) in cash and cash equivalents	2,432,726	24,725,325
Cash and cash equivalents at beginning of period	31,228,192	15,431,622
Cash and cash equivalents at end of period	$ 33,660,918	$ 40,156,947