Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss		$ (27,099)	$ (16,291)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation		5,600	5,167
Depreciation of property and equipment		276	227
Amortization of right-of-use assets		523
Noncash interest income, net		(1,061)	(480)
Changes in assets and liabilities:
Accounts receivable due from related party		2,058	50,926
Prepaids and other current assets		(340)	(475)
Other assets		117	53
Accounts payable		8	(378)
Other liabilities		29	2,480
Deferred revenue from related party		(13,272)	8,063
Net cash provided by (used in) operating activities		(33,161)	49,292
Investing activities
Purchases of property and equipment, net		(236)	(631)
Purchases of investments		(154,889)	(99,762)
Sales of investments		4,967
Maturities of investments		116,270	62,450
Net cash used in investing activities		(33,888)	(37,943)
Financing activities
Proceeds from issuance of common stock		73,276
Proceeds from exercise of stock options and employee stock purchase plan		5,604	7,881
Employees' tax withheld and paid for restricted stock units		(1,174)	(473)
Borrowings under credit facility agreement, net of issuance costs			9,975
Net cash provided by financing activities		77,706	17,383
Net increase in cash and cash equivalents		10,657	28,732
Cash and cash equivalents at beginning of period		28,088	40,020
Cash and cash equivalents at end of period		38,745	68,752
Supplemental disclosures of cash flow information
Cash paid for interest		871	$ 173
Right-of-use assets obtained in exchange for lease obligations	[1]	$ 2,796

[1] Amounts for the six months ended June 30, 2019 include the transition adjustment of $1,301 for the adoption of Topic 842.