CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net loss	$ (40,912)	$ (14,709)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation of property and equipment	44	41
Accretion of discount on investments	(917)	(162)
Share-based compensation expense	11,131	3,660
Changes in operating assets and liabilities:
Other current assets	(1,528)	502
Other long-term assets	1,229	25
Accounts payable, accrued liabilities, deferred revenue and other liabilities	(1,071)	2,745
Cash flows used in operating activities	(34,482)	(7,948)
Investing activities:
Purchases of short-term investments	127,458	102,820
Sales and maturities of short-term investments	92,250	17,742
Cash flows used in investing activities	(35,208)	(85,078)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	107,883	0
Proceeds from exercise of common stock options	2,668	5,890
Proceeds from disgorgement of stockholders' short-swing profits	1,050	0
Cash flows provided by financing activities	111,601	5,890
Increase (decrease) in cash and cash equivalents	41,911	(87,136)
Cash and cash equivalents, beginning of period	32,694	107,703
Cash and cash equivalents, end of period	$ 74,605	$ 20,567