Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net loss	$ (111,178)	$ (122,313)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	1,002	926
Amortization of premium on investment securities	250	759
Non-cash interest expense	5,095
Stock-based compensation expense	22,291	14,691
Remeasurement loss on embedded derivatives liabilities	666
Loss on assets disposal	26
Changes in operating assets and liabilities:
Prepaid research and development	3,812	(5,502)
Prepaid expenses and other current assets	(9,650)	(2,204)
Prepaid and other long-term assets	(1,063)	(4,025)
Accounts payable	(2,765)	(5,443)
Accrued compensation and employee benefits	754	(824)
Accrued research and development	(1,768)	(3,688)
Accrued and other liabilities	1,342	777
Deferred revenue	(8,915)	22,011
Other long-term liabilities	(432)	(371)
Net cash used in operating activities	(100,533)	(105,206)
Investing activities
Purchases of property and equipment	(304)	(1,803)
Decrease in restricted cash (SRX Cardio)	6	196
Purchase of intangible assets	(5,000)
Purchases of investments	(186,407)	(155,436)
Proceeds from maturities of investments	170,529	214,378
Net cash (used in) provided by investing activities	(21,176)	57,335
Financing activities
Proceeds from debt issuance, net	48,000
Payment of public offering cost		(242)
Debt issuance costs paid	(557)
Proceeds from issuance of common stock pursuant to equity award plans	9,623	972
Net cash provided by financing activities	57,066	730
Net decrease in cash and cash equivalents	(64,643)	(47,141)
Cash and cash equivalents at beginning of period	188,480	186,488
Cash and cash equivalents at end of period	$ 123,837	$ 139,347