Income Taxes - Reconciliation of Income Tax to Expense (Benefit) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 2,941	$ (27,491)	$ (16,109)
State taxes, net of federal benefit	(489)	(1,821)	(1,580)
Change in valuation allowance	7,013	22,602	21,990
Permanent interest disallowed	(8,608)	7,197	(4,466)
Other permanent differences	1,226	1,279	1,360
Research and development tax credits	(1,387)	(744)	(2,352)
State tax rate benefit	(503)	(822)	842
Credits and other	(109)	(200)	320
Provision for income tax benefit (expense)	$ 84us-gaap_IncomeTaxExpenseBenefit	$ 0us-gaap_IncomeTaxExpenseBenefit	$ 5us-gaap_IncomeTaxExpenseBenefit

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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