Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net loss	$ (50,038)	$ (29,281)	$ (17,708)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	1,539	1,777	1,947
Amortization of debt discount	51	213	136
Stock-based compensation	4,926	1,145	745
Revaluation of preferred stock warrant liability	0	(1,156)	387
Loss on extinguishment of debt	581	0	0
Amortization of premium on short-term investments	86	(518)	0
Interest accrued on long-term debt	(348)	259	90
Conversion of accrued interest to long-term debt	420	0	0
Loss on disposal of property and equipment	0	1	3
Gain on sale of investments	(5)	0	0
Changes in operating assets and liabilities
Accounts receivable, net	(4,109)	(5,009)	(210)
Inventory	(1,252)	(1,370)	(1,884)
Prepaid expenses and other	(2,132)	(1,679)	221
Other	(70)	(268)	118
Accounts payable	21	1,601	103
Accrued liabilities	3,379	2,678	1,830
Deferred revenue	9,497	1,025	146
Deferred rent	(607)	(764)	(732)
Net cash used in operating activities	(38,061)	(31,346)	(14,808)
Investing activities:
Purchases of property and equipment	(1,900)	(759)	(428)
Proceeds from sale of short-term investments	4,500	0	0
Proceeds from maturity of short-term investments	35,977	0	0
Purchases of short-term investments	(62,911)	(32,175)	0
Decrease (increase) in restricted cash	59	(21)	0
Net cash used in investing activities	(24,275)	(32,955)	(428)
Financing activities:
Proceeds from long-term debt	30,000	5,000	13,000
Deferred costs related to long-term debt	(770)	0	0
Repayment of long-term debt	(18,214)	(211)	(1,706)
Proceeds from public offering	57,015	47,374	0
Proceeds from exercise of common stock warrants	230	0	0
Proceeds from issuance of common stock for employee stock purchase plan	988	0	0
Proceeds from issuance of preferred stock and warrants	0	0	15,132
Repurchase of shares related to common stock warrant exercise	(94)	0	0
Deferred offering costs	0	0	(553)
Proceeds from exercise of stock options	411	387	187
Net cash provided by financing activities	69,566	52,550	26,060
Net increase (decrease) in cash and cash equivalents	7,230	(11,751)	10,824
Effect of exchange rate changes on cash and cash equivalents	52	0	0
Cash and cash equivalents:
Beginning of year	9,941	21,692	10,868
End of year	17,223	9,941	21,692
Supplemental disclosures:
Accretion of preferred stock	0	4,653	7,533
Accrual of offering costs	0	29	1,212
Cash paid for interest	3,479	1,474	563
Rental instruments reclassified from inventory	2,541	0	0
Issuance of preferred stock warrants with debt	0	138	648
Non-cash capital lease	262	410	0
Common Stock [Member]
Supplemental disclosures:
Conversion of convertible preferred stock to common stock	0	108,275	0
Warrants [Member]
Supplemental disclosures:
Conversion of convertible preferred stock to common stock	$ 0	$ 2,514	$ 0