Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities
Net loss	$ (57,636,873)	$ (25,313,037)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	32,827	5,820
Stock-based compensation	22,712,933	2,719,702
Non-cash research and development		15,296,515
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,907,823)	(90,502)
Accounts payable	1,051,266	501,844
Other long-term assets	(847,924)	(73,124)
Accrued expenses	4,261,747	646,882
Accrued indemnification obligation	135,500
Net cash used in operating activities	(33,198,347)	(6,305,900)
Cash flows from investing activities
Capital expenditures	(11,702,171)	(76,920)
Net cash used in investing activities	(11,702,171)	(76,920)
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	247,228,422
Payments of deferred offering costs	(1,198,220)
Proceeds from exercise of stock options	218,525	341,000
Proceeds from exercise of stock warrants	42,000	341,000
Net cash provided by financing activities	246,290,727	72,969,569
Net increase in cash and cash equivalents	201,390,209	66,586,749
Cash and cash equivalents, beginning of period	62,251,860	3,119,713
Cash and cash equivalents, end of period	263,642,069	69,706,462
Supplemental Cash Flow Information
Cash paid for interest		439
Supplemental Disclosure of Non-cash Investing and Financing Activities
Purchases of property and equipment in accounts payable and accrued liabilities	4,926,762
Deferred issuance costs for underwritten offering in accounts payable and accrued liabilities	$ 727,367
Deferred issuance costs for planned initial public offering in accrued expenses		322,914
Class B Preferred Stock
Cash flows from financing activities
Proceeds from issuance of preferred stock		2,500,000
Class C Preferred Stock
Cash flows from financing activities
Proceeds from issuance of preferred stock		5,000,020
Class D Preferred Stock
Cash flows from financing activities
Proceeds from issuance of preferred stock		$ 64,787,549