Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Deferred tax valuation allowance has been recorded against these assets	100.00%
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, alternative minimum tax	$ 19,500,000
Deferred tax assets [Abstract]
Net operating loss carryforwards	105,661,000	$ 86,541,000
Tax credit carryforwards	27,671,000	22,716,000
Equipment, furnishings and other	10,547,000	14,396,000
Total deferred tax assets	143,879,000	123,653,000
Deferred tax liabilities	(270,000)	(187,000)
Net deferred tax assets	143,609,000	123,466,000
Valuation allowance	(143,609,000)	(123,466,000)
Deferred Tax Assets, Net of Valuation Allowance	0	0
Net change in valuation allowance	20,100,000	23,400,000
Federal statutory rate to net loss before income taxes [Abstract]
Federal benefit at statutory rate	(19,919,000)	(10,240,000)	$ (16,145,000)
State income taxes, net of Federal taxes	(3,556,000)	(2,773,000)	(1,517,000)
State credits	(1,324,000)	(990,000)	(787,000)
Warranty liabilities	(1,509,000)	(6,477,000)	6,871,000
Other permanent differences	16,000	37,000	14,000
Provision related to change in valuation allowance	20,142,000	23,440,000	14,606,000
Current year tax credit	(2,050,000)	(1,300,000)	(1,034,000)
Return to provision	8,198,000	(1,504,000)	(2,011,000)
Other, net	3,000	(192,000)	5,000
Provision for income taxes	800	800	1,600
Change in unrecognized tax benefits	0
Unrecognized tax benefits accrued interest or penalties	$ 0	$ 0	$ 0
Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Expiration Date	Dec. 31, 2022
Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Expiration Date	Dec. 31, 2035
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 14,800,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	281,600,000
Federal [Member] | Restricted [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	62,300,000
Federal [Member] | Unrestricted [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	219,300,000
State [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 173,700,000