Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (60,133)	$ (45,098)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	884	562
Stock-based compensation	9,911	7,782
Non-cash interest expense	2,406	0
Change in fair value of embedded derivative liability	(531)	0
Net accretion of discounts and amortization of premiums of available-for-sale securities	216	(332)
Changes in assets and liabilities
Accrued interest of available-for-sale securities	(261)	(119)
Inventory	(75)	0
Prepaid expenses and other assets	356	(2,325)
Accounts receivable	791	515
Accounts payable	924	3,007
Accrued liabilities and other liabilities	3,509	(2,431)
Net cash used in operating activities	(42,003)	(38,439)
Cash flows from investing activities
Purchases of property and equipment	(936)	(1,222)
Purchases of available-for-sale securities	(56,524)	(95,528)
Maturities of available-for-sale securities	60,250	46,795
Net cash provided by (used in) investing activities	2,790	(49,955)
Cash flows from financing activities
Proceeds from issuance of long-term debt	34,600	0
Proceeds from public offerings, net of offering costs	0	61,822
Payment of debt issuance costs	(623)	0
Proceeds from issuance of common stock upon exercise of stock options	3,192	2,918
Proceeds from employee stock purchase plan	430	326
Net cash provided by financing activities	37,599	65,066
Net decrease in cash and cash equivalents	(1,614)	(23,328)
Cash and cash equivalents at beginning of period	23,735	33,104
Cash and cash equivalents at end of period	22,121	9,776
Supplemental disclosure of noncash investing and financing activities
Purchases of inventory in accounts payable and accrued expenses	337	0
Debt issuance costs in accounts payable and accrued expense	10	0
Purchases of property and equipment in accounts payable and accrued expense	51	227
Stock-based compensation capitalized in inventory	$ 13	$ 0