Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net loss	$ (89,490)	$ (60,058)	$ (51,802)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	1,194	808	435
Stock-based compensation	13,367	10,571	9,956
Non-cash interest expense	4,645	0	0
Change in fair value of embedded derivative liability	(294)	0	0
Net accretion of discounts and amortization of premiums of available-for-sale securities	456	(301)	875
Changes in assets and liabilities
Accrued interest of available-for-sale securities	(161)	(2)	110
Inventory	(1,646)	0	0
Prepaid expenses and other assets	(2,036)	2,643	(4,416)
Accounts receivable, net	427	490	(760)
Accounts payable	333	502	(788)
Accrued liabilities and other liabilities	6,378	(2,721)	(820)
Net cash used in operating activities	(66,827)	(48,068)	(47,210)
Cash flows from investing activities
Purchases of property and equipment	(1,258)	(1,624)	(1,399)
Purchases of available-for-sale securities	(62,510)	(103,528)	(59,828)
Maturities of available-for-sale securities	89,333	78,443	69,285
Net cash provided by (used in) investing activities	25,565	(26,709)	8,058
Cash flows from financing activities
Proceeds from issuance of long-term debt	99,600	0	0
Proceeds from public offerings, net of offering costs	0	61,822	9,657
Payment of debt issuance costs	(633)	0	0
Proceeds from issuance of common stock upon exercise of stock options	9,110	2,966	746
Proceeds from employee stock purchase plan	766	620	407
Net cash provided by financing activities	108,843	65,408	10,810
Net increase (decrease) in cash and cash equivalents	67,581	(9,369)	(28,342)
Cash and cash equivalents at beginning of period	23,735	33,104	61,446
Cash and cash equivalents at end of period	91,316	23,735	33,104
Supplemental disclosure
Cash paid for income taxes	0	0	4,691
Supplemental disclosure of noncash investing and financing activities
Purchases of property and equipment in accounts payable and accrued expense	61	148	161
Stock-based compensation capitalized in inventory	39	0	0
Stock option exercise settled after period end	$ 0	$ 76	$ 0