Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (54,963)	$ (30,993)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	311	336
Amortization of debt issuance costs	549	78
Stock-based compensation expense	7,783	4,730
Loss on extinguishment of debt	1,007
Loss on disposals of assets		3
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,304)	(695)
Other assets	14	(769)
Accounts payable	2,933	(1,409)
Accrued direct research and other current and long-term liabilities	10,836	7,290
Deferred revenue	(13,452)	(37,094)
Net cash used in operating activities	(46,286)	(58,523)
Investing activities
Purchases of property and equipment	(370)	(208)
Net cash used in investing activities	(370)	(208)
Financing activities
Proceeds from issuance of common stock	232,846	108,910
Payments on deferred offering costs		(386)
Proceeds from long-term debt	60,000	20,000
Payments on deferred issuance costs	(2,289)	(251)
Exercise of options	1,504	371
Payment of capital lease obligation		(45)
Net cash provided by financing activities	292,061	128,599
Net increase in cash and cash equivalents	245,405	69,868
Cash and cash equivalents at beginning of year	129,780	84,732
Cash and cash equivalents at end of period	375,185	154,600
Supplemental disclosures
Cash paid for interest	2,715	727
Purchases of equipment in accounts payable and other current liabilities	31	106
Accrued deferred offering costs	$ 22	$ 18