Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (194,119)	$ (213,349)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	1,667	1,423
Net amortization/accretion on investment securities	217	962
Non-cash interest expense	8,244
Stock-based compensation expense	32,405	22,464
Remeasurement loss on embedded derivatives liabilities	657
Loss on assets disposal	50
Changes in operating assets and liabilities:
Receivables from collaborators		(4,000)
Prepaid research and development	5,411	1,401
Prepaid expenses and other current assets	(6,087)	(1,537)
Prepaid and other long-term assets	(4,395)	5,677
Accounts payable	3,426	(1,286)
Accrued compensation and employee benefits	4,104	(1,942)
Accrued research and development	326	(8,762)
Accrued and other liabilities	2,081	(249)
Deferred revenue	(12,743)	16,689
Other long-term liabilities	(657)	(565)
Net cash used in operating activities	(159,413)	(183,074)
Investing activities
Purchases of property and equipment	(1,542)	(1,564)
Decrease (increase) in restricted cash (SRX Cardio)	8	(1,589)
Purchase of intangible assets	(5,000)
Purchases of investments	(373,976)	(197,650)
Proceeds from maturities of investments	250,293	294,619
Net cash (used in) provided by investing activities	(130,217)	93,816
Financing activities
Proceeds from debt issuance, net	48,000
Proceeds from issuance of common stock, net	380,552
Payment of public offering cost	(387)	(242)
Debt issuance costs paid	(557)
Proceeds from issuance of common stock pursuant to equity award plans	17,563	1,673
Net cash provided by financing activities	445,171	1,431
Net increase/ (decrease) in cash and cash equivalents	155,541	(87,827)
Cash and cash equivalents at beginning of period	188,480	186,488
Cash and cash equivalents at end of period	$ 344,021	$ 98,661