Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2002
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, unrestricted	$ 165,200,000
Tax credit carryforward related to research and development	12,200,000
Tax credit carryforwards related to alternative minimum tax	17,400,000
Expiration date	2022 through 2034
Deferred tax valuation allowance has been recorded against these assets (in hundredths)	100.00%
Deferred tax assets [Abstract]
Net operating loss carryforwards	86,541,000	69,989,000
Tax credit carryforwards	22,716,000	18,816,000
Equipment, furnishings and other	14,396,000	11,313,000
Total deferred tax assets	123,653,000	100,118,000
Deferred tax liabilities	(187,000)	(92,000)
Net deferred tax assets	123,466,000	100,026,000
Valuation allowance	(123,466,000)	(100,026,000)
Deferred Tax Assets, Net of Valuation Allowance	0	0
Net change in valuation allowance	23,400,000	14,600,000
Federal statutory rate to net loss before income taxes [Abstract]
Federal benefit at statutory rate	(10,240,000)	(16,145,000)	(6,107,000)
State income taxes, net of Federal taxes	(2,773,000)	(1,517,000)	(745,000)
State credits	(990,000)	(787,000)	(1,555,000)
Warranty liabilities	(6,477,000)	6,871,000	941,000
Other permanent differences	37,000	14,000	(23,000)
Provision related to change in valuation allowance	23,440,000	14,606,000	14,069,000
Current year tax credit	(1,300,000)	(1,034,000)	0
Return to provision	(1,504,000)	(2,011,000)	(6,578,000)
Other, net	(192,000)	5,000	0
Provision for income taxes	800	1,600	1,600
Change in unrecognized tax benefits	0
Unrecognized tax benefits accrued interest or penalties	0	0	0
Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, restricted				62,300,000
Operating loss carryforwards, unrestricted	227,500,000
State [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, unrestricted	$ 157,500,000