Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	$ 21,200,000
Deferred tax assets [Abstract]
Net operating loss carryforwards	126,244,000	$ 105,661,000
Tax credit carryforwards	29,970,000	27,671,000
Equipment, furnishings and other	9,297,000	10,547,000
Total deferred tax assets	165,511,000	143,879,000
Deferred tax liabilities	(301,000)	(270,000)
Net deferred tax assets	165,210,000	143,609,000
Valuation allowance	(165,210,000)	(143,609,000)
Deferred tax assets, net of valuation allowance	0	0
Net change in valuation allowance	21,400,000	20,100,000
Federal statutory rate to net loss before income taxes [Abstract]
Federal benefit at statutory rate	(17,262,000)	(19,919,000)	$ (10,240,000)
State income taxes, net of Federal taxes	(3,086,000)	(3,556,000)	(2,773,000)
State credits	(1,031,000)	(1,324,000)	(990,000)
Warranty liabilities	(1,301,000)	(1,509,000)	(6,477,000)
Other permanent differences	40,000	16,000	37,000
Provision related to change in valuation allowance	21,601,000	20,142,000	23,440,000
Current year tax credit	(1,119,000)	(2,050,000)	(1,300,000)
Return to provision	2,156,000	8,198,000	(1,504,000)
Other, net	3,000	3,000	(192,000)
Provision for income taxes	800	800	800
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, 2036
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 16,000,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	333,500,000
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	271,200,000
State [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 224,000,000