Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:
Net loss	$ (80,856)	$ (47,386)	$ (83,903)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	8,006	6,157	4,809
Stock-based compensation, restructuring	201	0	0
Depreciation	1,806	1,599	1,584
Amortization of debt issuance costs and non-cash interest	569	2,017	1,793
Change in fair value of warrant liabilities	21,927	(11,811)	(445)
Change in fair value of embedded derivatives	(759)	147	240
Loss on disposal and impairment of property and equipment	0	9	0
Changes in operating assets and liabilities:
Trade accounts receivable	(1,022)	(730)	(439)
Inventory	2,950	3,890	1,517
Prepaid expenses and other current assets	(2,004)	163	24
Other assets	(1,747)	11	338
Accounts payable and accrued expenses	6,142	2,194	4,898
Restructuring liabilities	4	0	0
Deferred revenue	(137)	(8,462)	(10,887)
Net cash used in operating activities	(44,920)	(52,202)	(80,471)
Investing activities:
Purchases of property and equipment	(810)	(293)	(617)
Net cash used in investing activities	(810)	(293)	(617)
Financing activities:
Proceeds from borrowings of debt and revolving credit facility, net of issuance costs	0	9,900	39,124
Payments on borrowings of debt	0	(25,000)	(825)
Payments on revolving credit facility	0	(15,051)	(9,477)
Proceeds from exercise of common stock options and warrants	833	33	92
Proceeds from issuance of common stock and common stock warrants, net of issuance costs	75,690	67,316	59,527
Net cash provided by financing activities	76,523	37,198	88,441
Net (decrease) increase in cash and cash equivalents	30,793	(15,297)	7,353
Cash and cash equivalents at beginning of period	41,228	56,525	49,172
Cash and cash equivalents at end of period	72,021	41,228	56,525
Supplemental disclosure of cash flow information:
Cash paid for interest	2,463	5,284	4,186
Noncash investing and financing activities:
Purchase of property and equipment in accounts payable	446	0	123
Change in common stock warrant liability associated with exercise of warrants	(79)	0	0
Warrants issued in connection with public offering	0	20,959	0
Asset retirement obligation	0	286	0
Warrants issued in connection with debt	0	0	866
Embedded derivatives related to debt	0	0	605
Vesting of early exercised stock options	$ 0	$ 0	$ 15