Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017
Cash flow from operating activities
Net loss	$ (12,954)		$ (7,200)
Adjustments to reconcile net earnings to net cash used in operating activities:
Stock-based compensation expense	656		72
Depreciation and amortization	828		486
Share of loss from equity method investee	226		70
Other non-operating income	(59)		(30)
Changes in operating assets and liabilities
Amounts owed by a related party	(29)		405
Prepaid expenses and other current assets	(693)		(96)
Accounts payable	(306)		(2,692)
Accrued liabilities	410		(469)
Other current liabilities	9		10
Deferred revenue	(1,250)
Deferred rent	(85)		(153)
Net cash used in operating activities	(13,247)		(9,597)
Cash flow from investing activities
Purchase of short-term and long-term investments	(41,084)		(21,354)
Proceeds from maturities of short-term investments	25,647		7,000
Purchase of property and equipment	(1,054)		(2,139)
Net cash used in investing activities	(16,491)		(16,493)
Cash flow from financing activities
Proceeds from initial public offering, net of issuance costs	126,259
Proceeds from issuance of common stock upon exercise of stock options, net of repurchases	3,304		29
Payment of preferred stock issuance costs	(135)
Net cash provided by financing activities	129,428		29
Net decrease in cash and cash equivalents	99,690		(26,061)
Cash and cash equivalents at beginning of period	98,426	[1]	65,160
Cash and cash equivalents at end of period	198,116		39,099
Non-cash investing and financing activities:
Unpaid financing cost included in accounts payable and accrued liabilities	1,170
Purchase of property and equipment purchases included in accounts payable and accrued liabilities	695		1,100
Vesting of early exercised options and restricted stock	$ 278		$ 22

[1] The Condensed Consolidated Balance Sheet as of December 31, 2017 has been derived from the audited financial statements as of that date.