CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net income (loss)	$ (43,887,573)	$ (41,269,749)	$ 5,459,477
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	919,809	886,710	857,055
Stock-based compensation	9,322,127	6,920,220	8,025,261
Loss on disposal of property and equipment	0	10,639	6,100
Accretion of bond premium	395,116	1,310,238	1,615,063
Net realized foreign currency translation loss	0	51,944	0
Change in operating assets and liabilities:
Receivables	191,555	856,372	5,490,605
Prepaid expenses and other assets	(517,318)	(96,582)	2,711,331
Accounts payable	(252,605)	(60,713)	(3,700,175)
Accrued wages, benefits and other liabilities	(771,866)	(777,204)	(2,923,537)
Deferred revenue	(50,000)	(50,000)	(59,746,948)
Net cash used in operating activities	(34,650,755)	(32,218,125)	(42,205,768)
Investing activities
Purchases of property and equipment	(713,839)	(341,616)	(1,501,744)
Proceeds from disposal of property and equipment	0	0	10,000
Purchases of investments	(139,932,358)	(86,281,946)	(149,370,678)
Proceeds from sale and maturities of investments	190,765,053	88,114,199	82,302,191
Net cash provided by investing activities	50,118,856	1,490,637	(68,560,231)
Financing activities
Stock repurchase	(164,472)	(57,274)	(3,814)
Proceeds from public offering	0	0	101,904,977
Proceeds from the exercise of stock options	261,082	379,290	1,290,886
Proceeds from stock purchases under employee stock purchase plan	231,859	305,003	299,229
Net cash provided by financing activities	328,469	627,019	103,491,278
Effect of exchange rate	0	(1,352)	(38,776)
Net increase (decrease) in cash and cash equivalents	15,796,570	(30,101,821)	(7,313,497)
Cash and cash equivalents at beginning of period	15,431,622	45,533,443	52,846,940
Cash and cash equivalents at end of period	$ 31,228,192	$ 15,431,622	$ 45,533,443