Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating Activities:
Net loss	$ (49,670)	$ (41,477)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,668	1,030
Amortization of (discount) premium on marketable securities	(4,043)	(310)
Stock-based compensation	10,374	6,969
Taxes paid related to net share settlement of equity awards		(71)
Other	715
Net changes in operating assets and liabilities:
Interest receivable	(443)	(259)
Accounts receivable	(2,225)	1,539
Prepaid expenses and other assets	(1,851)	(743)
Accounts payable and accrued liabilities	789	3,676
Accrued compensation and employee benefits	1,127	1,589
Non-current liabilities	1,730
Deferred revenues	118,540	56,078
Net cash provided by operating activities	76,711	28,021
Investing Activities:
Purchases of marketable securities	(451,239)	(229,595)
Maturities of marketable securities	230,547	127,093
Purchases of property and equipment	(15,028)	(2,873)
Other investment	(5,221)
Net cash used in investing activities	(240,941)	(105,375)
Financing Activities:
Proceeds from public offering of common stock, net of issuance costs	215,757	81,573
Taxes paid related to net share settlement of equity awards	(83)
Proceeds from issuance of common stock	14,469	3,614
Net cash provided by financing activities	230,143	85,187
Net increase in cash, cash equivalents, and restricted cash	65,913	7,833
Cash, cash equivalents, and restricted cash, beginning of period	53,326	22,061
Cash, cash equivalents, and restricted cash, end of period	119,239	29,894
Property and Equipment [Member]
Supplemental disclosure of noncash investing activities:
Property and equipment included in accrued liabilities	$ 5,813	$ 50