Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (38,820,998)	$ (28,078,646)	$ (12,201,386)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,305,070	2,899,304	1,297,985
Warrant remeasurement	0	1,879,823	(582,360)
Depreciation expense	100,117	53,116	31,229
Loss on disposal of fixed assets	102,788	0	0
Amortization of debt discount	75,214	104,311	35,288
Amortization of debt issuance costs	90,800	94,648	0
Non-cash interest expense	175,909	38,521	6,384
Changes in assets and liabilities:
Other receivable	0	0	459,018
Prepaid expenses and other assets	38,794	(814,156)	(96,754)
Accounts payable	1,420,556	(71,751)	526,869
Accrued expenses	(676,918)	2,142,187	808,514
Net cash used in operating activities	(32,188,668)	(21,752,643)	(9,715,213)
Cash flows from investing activities:
Purchases of property and equipment	(686,705)	(1,305,086)	(884,793)
Net cash used in investing activities	(686,705)	(1,305,086)	(884,793)
Cash flows from financing activities:
Proceeds from issuance of debt	11,022,286	3,000,000	3,000,000
Proceeds from exercise of stock options	293,988	1,094	0
Proceeds from exercise of warrants	20,970	0	0
Payments for issuance costs	(544,773)	(1,402,845)	(1,351,450)
Payments for debt issuance costs	(219,042)	0	(94,998)
Repayment of debt	(1,488,558)	(533,729)	0
Proceeds from issuance of common stock, net of underwriting costs	0	86,059,087	0
Proceeds from issuance of preferred stock, net of issuance costs	0	52,394,571	14,917,257
Net cash provided by financing activities	9,084,871	139,518,178	16,470,809
Net (decrease) increase in cash	(23,790,502)	116,460,449	5,870,803
Cash and cash equivalents at beginning of period	130,189,421	13,728,972	7,858,169
Cash and cash equivalents at end of period	106,398,919	130,189,421	13,728,972
Cash paid for:
Interest	790,402	559,175	82,729
Supplemental cash flow information:
Conversion of Preferred Stock to Common Stock	0	93,364,275	0
Conversion of Preferred Stock Warrants to Common Stock Warrants	0	3,726,043	0
Deferred issuance costs included in accrued expenses and accounts payable	0	549,178	53,946
Non-cash financing costs	0	175,114	0
Accrued capital expenditures included in accrued expenses and accounts payable	$ 167,285	$ 71,040	$ 450,373