Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes
United States	$ 10,408,000	$ 2,335,000	$ 23,902,000
Foreign	892,000	361,000	(17,000)
Income before income taxes	11,300,000	2,696,000	23,885,000
Federal
Current	(155,000)	175,000	1,373,000
Deferred	(3,755,000)	707,000	9,783,000
Total	(3,910,000)	882,000	11,156,000
State
Current	123,000	37,000	(331,000)
Deferred	(634,000)	242,000	(1,448,000)
Total	(511,000)	279,000	(1,779,000)
Foreign
Current	95,000
Total	95,000
Total
Current	63,000	212,000	1,042,000
Deferred	(4,389,000)	949,000	8,335,000
Total	(4,326,000)	1,161,000	9,377,000
Reconciliation of the federal income tax expense at the statutory rate to the effective income tax expense
Statutory federal income tax expense	3,842,000	916,000	8,147,000
State taxes, net of federal benefit	(338,000)	185,000	(38,000)
Foreign tax paid	95,000
State income tax apportionment adjustment			(1,137,000)
Extraterritorial income exclusion			(7,000)
Tax consequences of the sale of engines to WMES	(36,000)	(46,000)	1,214,000
Uncertain tax positions	160,000	97,000	195,000
Permanent differences-162(m)	732,000	385,000	737,000
ETI basis restoration	(8,728,000)
Permanent differences and other	(53,000)	(376,000)	266,000
Total	(4,326,000)	1,161,000	9,377,000
Reconciliation of the federal income tax expense
Statutory federal income tax expense (as a percent)	34.00%	34.00%	34.00%
State taxes, net of federal benefit (as a percent)	(3.00%)	6.90%	(0.20%)
Foreign tax paid (as a percent)	0.80%
State income tax apportionment adjustment (as a percent)			(4.70%)
Tax consequences of the sale of engines to WMES (as a percent)	(0.30%)	(1.70%)	5.10%
Uncertain tax positions (as a percent)	1.40%	3.60%	0.80%
Permanent differences-162(m) (as a percent)	6.50%	14.30%	3.10%
ETI basis restoration (as a percent)	(77.20%)
Permanent differences and other (as a percent)	(0.50%)	(14.10%)	1.00%
Effective income tax expense (benefit) (as a percent)	(38.30%)	43.00%	39.10%
Effective tax rate reduced, related to change in California state tax			1,100,000
Income tax benefit related to extraterritorial income	$ 8,700,000