Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net loss	$ (83,011,804)	$ (38,473,844)	$ (15,705,776)
Adjustments to reconcile net loss to net cash used in operating activities:
Loss on sale of discontinued operations			145,199
Depreciation and amortization	64,630	13,463	3,350
Employee stock-based compensation	26,785,770	5,250,217	1,204,261
Stock-based third-party research and development		20,154,076	6,207,993
Disposal of fixed assets	24,011
Loss on extinguishment of debt			116,260
Changes in operating assets and liabilities
Prepaid and other current assets	(3,854,389)	(886,986)	(22,643)
Other long-term assets	(1,132,084)	(1,311,736)	(4,433)
Accounts payable	957,986	276,231	(92,582)
Accrued expenses	11,773,185	1,182,611	58,103
Accrued indemnification obligation	372,000		4,080,500
Other		(57)
Net cash provided by discontinued operations			8,731
Net cash used in operating activities	(48,020,695)	(13,796,025)	(4,001,037)
Cash flows from investing activities
Capital expenditures	(19,182,085)	(221,003)	(29,284)
Net cash used in investing activities	(19,182,085)	(221,003)	(29,284)
Cash flows from financing activities
Proceeds from issuance of convertible notes			1,000,000
Proceeds from exercise of stock options	429,714	520,606
Proceeds from exercise of stock warrants	53,350	341,000
Re-payment of notes payable			(350,000)
Proceeds from IPO and Follow-On Offering, net of issuance costs	246,489,901
Payment of deferred IPO costs	(1,592,206)
Net cash provided by financing activities	245,380,759	73,149,175	7,150,034
Net increase in cash and cash equivalents	178,177,979	59,132,147	3,119,713
Cash and cash equivalents, Beginning of Period	62,251,860	3,119,713
Cash and cash equivalents, End of Period	$ 240,429,839	62,251,860	3,119,713
Supplemental Cash Flow Information
Cash paid for interest		14,745	35,025
Supplemental Disclosure of Non-cash Investing and Financing Activities
Conversion of accrued legal fees into common stock			102,300
Conversion of convertible notes into Class B-1 and Class C preferred stock			1,000,000
Deferred issuance costs for planned initial public offering in accrued expenses		371,043
Class B Preferred Stock
Cash flows from financing activities
Proceeds from issuance of common stock		2,500,000	2,000,000
Class C Preferred Stock
Cash flows from financing activities
Proceeds from issuance of common stock		5,000,020	$ 4,500,034
Class D Preferred Stock
Cash flows from financing activities
Proceeds from issuance of common stock		$ 64,787,549