Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities:
Net loss	$ (20,187)	$ (16,632)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	588	301
Amortization of (discount) premium on marketable securities	(459)	60
Stock-based compensation	3,050	2,788
Other	217	72
Net changes in operating assets and liabilities:
Interest receivable	(133)	(174)
Accounts receivable	(232)	2,571
Prepaid expenses and other assets	(1,334)	70
Accounts payable and accrued liabilities	(77)	(418)
Accrued compensation and employee benefits	(2,268)	(846)
Deferred revenues	2,701	(870)
Net cash used in operating activities	(18,134)	(13,078)
Investing Activities:
Purchases of marketable securities	(63,401)	(38,973)
Maturities of marketable securities	54,450	45,500
Purchases of property and equipment	(2,616)	(468)
Net cash (used in) provided by investing activities	(11,567)	6,059
Financing Activities:
Proceeds from public offering of common stock, net of issuance costs		3,425
Taxes paid related to net share settlement of equity awards	(14)	(4)
Proceeds from issuance of common stock	10,597	23
Net cash provided by financing activities	10,583	3,444
Net decrease in cash, cash equivalents, and restricted cash	(19,118)	(3,575)
Cash, cash equivalents, and restricted cash, beginning of period	53,326	22,061
Cash, cash equivalents, and restricted cash, end of period	34,208	18,486
Supplemental disclosure of noncash investing activities:
License included in accrued liabilities		950
Property and Equipment [Member]
Supplemental disclosure of noncash investing activities:
Property and equipment included in accrued liabilities	$ 1,227	$ 536