Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Net loss	$ (45,581)	$ (50,038)	$ (29,281)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	2,377	1,590	1,990
Stock-based compensation	6,278	4,926	1,145
Revaluation of preferred stock warrant liability	0	0	(1,156)
Loss on extinguishment of debt	0	581	0
Amortization of premium on short-term investments	270	86	(518)
Interest accrued on long-term debt	18	(348)	259
Conversion of accrued interest to long-term debt	1,067	420	0
Bad debt expense	34	0	0
Loss on disposal of property and equipment	3	0	1
Gain on sale of investments	0	(5)	0
Changes in operating assets and liabilities
Accounts receivable, net	(7,328)	(4,109)	(5,009)
Inventory	(5,354)	(1,252)	(1,370)
Prepaid expenses and other	1,199	(2,132)	(1,679)
Other assets	(7)	(70)	(268)
Accounts payable	(166)	21	1,601
Accrued liabilities	1,162	3,379	2,678
Deferred revenue	(127)	9,497	1,025
Deferred rent	2,793	(607)	(764)
Net cash used in operating activities	(43,362)	(38,061)	(31,346)
Investing activities:
Purchases of property and equipment	(3,796)	(1,900)	(759)
Proceeds from sale of short-term investments	3,000	4,500	0
Proceeds from maturity of short-term investments	57,309	35,977	0
Purchases of short-term investments	(32,750)	(62,911)	(32,175)
Proceeds from sale of property and equipment	6	0	0
Decrease (increase) in restricted cash	0	59	(21)
Net cash provided by (used in) investing activities	23,769	(24,275)	(32,955)
Financing activities:
Proceeds from long-term debt	10,000	30,000	5,000
Deferred costs related to long-term debt	0	(770)	0
Repayment of long-term debt and lease financing obligations	(271)	(18,214)	(211)
Net proceeds from public offerings of common stock	12,518	57,015	47,374
Proceeds from exercise of common stock warrants	2	230	0
Proceeds from issuance of common stock for employee stock purchase plan	1,295	988	0
Repurchase of shares related to common stock warrant exercise	0	(94)	0
Deferred offering costs	(152)	0	0
Proceeds from exercise of stock options	876	411	387
Net cash provided by financing activities	24,268	69,566	52,550
Net increase (decrease) in cash and cash equivalents	4,675	7,230	(11,751)
Effect of exchange rate changes on cash and cash equivalents	(42)	52	0
Cash and cash equivalents:
Beginning of year	17,223	9,941	21,692
End of year	21,856	17,223	9,941
Supplemental disclosures:
Cash paid for interest	2,844	3,479	1,474
Cash paid for taxes	69	0	0
Accrual of construction costs for leasehold improvements	640	0	0
Rental instruments reclassified from inventory	772	2,541	0
Non-cash inventory exchange for services	112	0	0
Non-cash capital lease	48	262	410
Accrual of offering costs	29	0	29
Accretion of preferred stock	0	0	4,653
Issuance of preferred stock warrants with debt	0	0	138
Common Stock [Member]
Operating activities:
Net loss	0
Supplemental disclosures:
Conversion of convertible preferred stock to common stock	0	0	108,275
Warrants [Member]
Supplemental disclosures:
Conversion of convertible preferred stock to common stock	$ 0	$ 0	$ 2,514