Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (39,203,719)	$ (27,471,094)	$ (14,325,484)
Adjustments to reconcile net loss to net cash used in operating activities:
Loss (gain) on disposal of assets	(577,314)	(4,562)	24,845
Depreciation and amortization	1,069,547	378,711	234,813
Stock-based compensation expense	7,504,316	3,946,027	2,070,194
Accretion of final fee premium	390,548	346,157	248,799
Amortization of discount on debt	173,803	88,123	57,117
Amortization of premiums on short-term investments	107,261	0	0
Deferred rent	(201,037)	0	0
Interest income accrued on short-term investments	(84,182)	0	0
Change in fair value of derivative financial instruments—warrants	(2,462,137)	726,421	(1,425,850)
Changes in operating assets and liabilities:
Increase in other assets	(789,739)	(37,296)	(258)
(Increase) decrease in accounts receivable	(1,724)	(42,042)	22,300
Increase in prepaid expenses	(277,327)	(420,026)	(216,470)
Increase in accounts payable and accrued expenses	2,157,221	361,432	632,299
Net cash used in operating activities	(31,039,855)	(22,119,025)	(12,727,385)
Investing activities
Capital expenditures	(823,483)	(2,241,066)	(363,290)
Proceeds from disposals of capital equipment	0	7,600	63,500
Maturities of short-term investments	13,750,000	0	0
Purchases of short-term investments	(37,760,166)	0	0
Net cash used in investing activities	(24,833,649)	(2,233,466)	(299,790)
Financing activities
Proceeds from sale of common stock, net of expenses	2,285,415	61,215,399	0
Proceeds from exercise of warrants		1,389,427
Proceeds from exercise of options	366,966	860,852	0
Borrowings under equipment line of credit	792,251	1,086,062
Repayments under equipment line of credit	(52,175)	0	(515,964)
Borrowings under long-term debt, net of costs	7,805,085		15,000,000
Repayments of long-term debt	(8,896,166)	0	0
Net cash provided by financing activities	2,301,376	64,551,740	14,484,036
Effect of exchange rate changes on cash and cash equivalents	(5,825)	0	0
Net change in cash and cash equivalents	(53,577,953)	40,199,249	1,456,861
Cash and cash equivalents—Beginning of period	67,493,047	27,293,798	25,836,937
Cash and cash equivalents—End of period	13,915,094	67,493,047	27,293,798
Supplementary disclosure of cash flow activity:
Cash paid for taxes	4,560	16,934	2,400
Cash paid for interest	1,103,677	1,061,993	425,256
Supplemental disclosure of non-cash investing and financing activities:
Warrants issued in connection with long-term debt	148,885		235,857
Reclassification of derivative financial instruments to additional paid-in capital		435,365	0
Preferred stock dividends accrued	24,240	24,240	23,015
Leasehold improvements paid for by lessor	$ 1,860,000	$ 0	$ 0