Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net loss	$ (68,964,000)	$ (36,773,000)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	734,000	572,000
Stock-based compensation	7,890,000	6,649,000
Accretion of interest expense	9,938,000	729,000
Change in fair value of embedded derivative liability	44,000	0
Net accretion of discounts and amortization of premiums of available-for-sale securities	(344,000)	(71,000)
Changes in assets and liabilities
Accrued interest of available-for-sale securities	(234,000)	(50,000)
Inventory	(1,726,000)	0
Prepaid expenses and other assets	(4,979,000)	730,000
Accounts receivable, net	(3,045,000)	760,000
Accounts payable	3,861,000	509,000
Accrued liabilities and other liabilities	(558,000)	325,000
Net cash used in operating activities	(57,383,000)	(26,620,000)
Cash flows from investing activities
Purchases of property and equipment	(497,000)	(621,000)
Purchases of available-for-sale securities	(183,796,000)	(40,071,000)
Maturities of available-for-sale securities	53,560,000	41,100,000
Net cash provided by (used in) investing activities	(130,733,000)	408,000
Cash flows from financing activities
Proceeds from public offerings, net of offering costs	134,268,000	0
Proceeds from issuance of long-term debt	0	34,600,000
Payment of debt issuance costs	0	(136,000)
Proceeds from issuance of common stock upon exercise of stock options	2,293,000	1,201,000
Proceeds from employee stock purchase plan	843,000	430,000
Net cash provided by financing activities	137,404,000	36,095,000
Net increase (decrease) in cash and cash equivalents	(50,712,000)	9,883,000
Cash and cash equivalents at beginning of period	91,316,000	23,735,000
Cash and cash equivalents at end of period	40,604,000	33,618,000
Supplemental disclosure of noncash investing and financing activities
Purchases of inventory in accounts payable and accrued expenses	236,000	0
Debt issuance costs in accounts payable and accrued expense	0	460,000
Purchases of property and equipment in accounts payable and accrued expense	10,000	51,000
Stock-based compensation capitalized in inventory	122,000	0
Public offering costs in accounts payable and accrued expense	$ 240,000	$ 0