Consolidated Statements of Cash Flows - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (128,154)	$ (137,628)	$ (100,327)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	7,501	7,143	6,176
Impairment of assets	1,544	576	2,138
Stock-based compensation	14,198	11,402	10,601
Inventory excess adjustments	265	502	2,110
Provision for doubtful accounts	(41)	143	984
Premium amortization and discount accretion on investment securities	238	857	1,445
Loss (gain) realized on investment securities	43	64	(191)
(Gain) loss on sales of property and equipment	(12)	12
Loss (gain) from changes in fair value of warrants	4,118	(1,148)	143
Interest accrued for borrowings and claims related settlement	2,172	488	533
Amortization of debt discount	391	154
Changes in operating assets and liabilities
Accounts receivable	(18,093)	6,315	(3,956)
Inventory	(4,900)	(3,086)	(431)
Prepaid expenses and other current assets	2,643	(1,515)	(2,077)
Other assets	335	600	(2,812)
Accounts payable	3,781	217	1,256
Accrued compensation	3,069	(1,467)	2,515
Other accrued liabilities	(1,820)	14,919	(378)
Deferred revenue	42,769	846	430
Deferred rent, net of current portion	(628)	1,452	7,789
Other long-term liabilities		1,329
Net cash used in operating activities	(70,581)	(97,825)	(74,052)
Investing activities
Purchases of investments	(170,268)	(272,819)	(53,522)
Proceeds from sale of investments	37,387	65,270	59,185
Proceeds from maturity of investments	131,600	231,200	64,500
Purchases of property and equipment, net	(3,880)	(9,867)	(23,136)
Net cash (used in) provided by investing activities	(5,161)	13,784	47,027
Financing activities
Proceeds from exercise of stock options	13,331	2,315	3,595
Proceeds from issuance of common stock under employee stock purchase plan	3,617	3,344	2,589
Proceeds from equity offering, net of issuance costs	96,777
Borrowings under long-term debt facility		75,000
Payment for debt issuance costs on long-term debt facility		(287)
Borrowings under credit facility			8,000
Repayment under credit facility			(1,000)
Net cash provided by financing activities	113,725	80,372	13,184
Net increase (decrease) in cash, cash equivalents and restricted cash	37,983	(3,669)	(13,841)
Cash, cash equivalents and restricted cash, beginning of period	13,021	16,690	30,531
Cash, cash equivalents and restricted cash, end of period	51,004	13,021	16,690
Supplemental disclosure of cash flow information:
Cash paid for income taxes	332	177
Cash paid for interest	7,914	3,568
Non-cash investing and financing activities:
Purchases of property and equipment through accounts payable and accruals	$ 268	$ 447	$ 5,204
Issuance of common stock for exercise of warrants	6,762
Issuance of common stock for lender's commitment to debt financing		2,448