Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Operating activities
Net loss		$ (11,949)	$ (9,417)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation		2,702	2,541
Depreciation of property and equipment		141	111
Amortization of right-of-use assets		239
Noncash interest income, net		(436)	(366)
Changes in assets and liabilities:
Accounts receivable due from related party		1,891	49,392
Prepaids and other current assets		(1,778)	(83)
Other assets		180	32
Accounts payable		327	(951)
Other liabilities		(1,443)	(1,372)
Deferred revenue from related party		(8,160)	1,061
Net cash provided by (used in) operating activities		(18,286)	40,948
Investing activities
Purchases of property and equipment, net		(46)	(32)
Purchases of investments		(75,235)	(77,941)
Sales of investments		4,967
Maturities of investments		65,170	26,900
Net cash used in investing activities		(5,144)	(51,073)
Financing activities
Proceeds from issuance of common stock		73,276
Proceeds from exercise of stock options		2,573	1,128
Employees' tax withheld and paid for restricted stock units		(1,174)	(473)
Net cash provided by financing activities		74,675	655
Net increase (decrease) in cash and cash equivalents		51,245	(9,470)
Cash and cash equivalents at beginning of period		28,088	40,020
Cash and cash equivalents at end of period		79,333	30,550
Supplemental disclosures of cash flow information
Cash paid for interest		422	$ 70
Right-of-use assets obtained in exchange for lease obligations	[1]	$ 1,301

[1] Amounts for the three months ended March 31, 2019 include the transition adjustment for the adoption of Topic 842.