Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income (loss)	$ (66,324)	$ (47,611)	$ (56,142)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	10,183	10,061	9,684
Write-off of construction in progress		3,440
Loss on disposal of assets	119	230	2,489
Debt issuance costs and noncash interest expenses	47	998	2,959
Write-off of costs associated with postponed public offering		241
Accretion of debt to fair value	50,011	18,696	18,678
Gain on extinguishment of convertible notes		(8,898)
Loss on exchange of convertible notes		5,697
Issuance of Series C preferred stock warrants in connection with senior convertible notes		10,677
Stock compensation expense	8,781	4,426	1,654
Loss on extinguishment of debt			1,379
Other	(31)	(25)	(2)
Changes in operating assets and liabilities:
Accounts receivable	838	(4,809)	(6,796)
Inventories	1,995	(547)	3,177
Prepaid expenses and other assets	(129)	(287)	(2)
Accounts payable	687	(1,686)	1,676
Accrued expenses	774	2,297	1,086
Deferred revenue	(303)	(588)	281
Other liabilities		(6,000)	(6,000)
Net cash provided by (used in) operating activities	6,648	(13,688)	(25,879)
Cash flows from investing activities:
Capital expenditures	(13,241)	(3,329)	(10,236)
Decrease in restricted cash			451
Net cash used in investing activities	(13,241)	(3,329)	(9,785)
Cash flows from financing activities:
Borrowings under line of credit	4,500	19,929	25,515
Repayments under line of credit	(5,500)	(20,267)	(24,177)
Proceeds from issuance of long-term debt		18,500	24,890
Repayment of borrowings under long-term debt	(18,849)
Financing costs	(47)	(872)	(425)
Proceeds from initial public offering	74,712
Repayment of obligations under capital lease	(80)	(42)	(42)
Proceeds from issuance of common stock	2		5
Net cash provided by financing activities	54,738	17,248	25,766
Net increase (decrease) in cash	48,145	231	(9,898)
Cash at beginning of period	1,574	1,343	11,241
Cash at end of period	49,719	1,574	1,343
Supplemental disclosures of cash flow information:
Interest paid	223	228	152
Income taxes paid	0	0	0
Supplemental disclosures of non-cash activities:
Conversion of convertible and senior convertible notes to common stock	168,510
Accrued dividends on preferred stock		996	4,191
Changes in redemption value of redeemable convertible preferred stock		(86,161)	(51,392)
Reclassification of redeemable convertible preferred stock from temporary to permanent equity		(1,085)
Changes in accrued capital expenditures	6,401	(523)	(38)
Capitalized interest	34	70	2,270
Capital lease	$ 5	$ 160