CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (24,115,400)	$ (21,473,947)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	444,396	442,986
Stock-based compensation	6,549,276	3,533,936
Loss on disposal of property and equipment		1,106
Accretion of bond premium	268,695	713,939
Change in operating assets and liabilities:
Receivables	240,285	722,855
Prepaid expenses and other assets	85,334	(361,415)
Accounts payable	(219,119)	170,661
Accrued wages, benefits and other liabilities	(1,749,432)	(1,735,378)
Deferred revenue	(25,000)	(25,000)
Net cash used in operating activities	(18,520,965)	(18,010,257)
Investing activities
Purchases of property and equipment	(466,388)	(94,720)
Purchases of investments	(88,909,817)	(34,703,423)
Proceeds from sale and maturities of investments	118,965,000	34,866,376
Net cash provided by investing activities	29,588,795	68,233
Financing activities
Stock repurchase	(158,284)	(57,274)
Proceeds from the exercise of stock options	109,307	333,128
Proceeds from stock purchases under employee stock purchase plan	137,925	169,952
Net cash provided by financing activities	88,948	445,806
Effect of exchange rate		(1,281)
Net increase (decrease) in cash and cash equivalents	11,156,778	(17,497,499)
Cash and cash equivalents at beginning of period	15,431,622	45,533,443
Cash and cash equivalents at end of period	$ 26,588,400	$ 28,035,944