Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities
Net loss	$ (41,764)	$ (64,974)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	504	457
Amortization of premium on investment securities	161	474
Non-cash interest expense	1,639
Stock-based compensation expense	9,034	7,069
Changes in operating assets and liabilities:
Prepaid research and development	1,401	6,122
Prepaid expenses and other current assets	(632)	(236)
Prepaid and other long-term assets	1,046	816
Accounts payable	(5,123)	3,344
Accrued compensation and employee benefits	(1,407)	(2,750)
Accrued research and development	(12,649)	(6,621)
Accrued and other liabilities	1,587	137
Deferred revenue	(5,128)	17,992
Other long-term liabilities	(205)	(166)
Net cash used in operating activities	(51,536)	(38,336)
Investing activities
Purchases of property and equipment	(113)	(1,335)
Decrease in restricted cash (SRX Cardio)	4	79
Purchases of investments	(147,781)	(52,544)
Proceeds from maturities of investments	95,304	115,684
Net cash (used in) provided by investing activities	(52,586)	61,884
Financing activities
Proceeds from debt issuance, net	48,000
Payment of public offering cost		(242)
Debt issuance costs paid	(536)
Proceeds from issuance of common stock pursuant to equity award plans	3,847	910
Net cash provided by financing activities	51,311	668
Net (decrease) increase in cash and cash equivalents	(52,811)	24,216
Cash and cash equivalents at beginning of period	188,480	186,488
Cash and cash equivalents at end of period	$ 135,669	$ 210,704