Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Federal
Current	$ 175,000	$ 1,373,000	$ (458,000)
Deferred	707,000	9,783,000	7,609,000
Total	882,000	11,156,000	7,151,000
State
Current	37,000	(331,000)	321,000
Deferred	242,000	(1,448,000)	158,000
Total	279,000	(1,779,000)	479,000
Total
Current	212,000	1,042,000	(137,000)
Deferred	949,000	8,335,000	7,767,000
Total	1,161,000	9,377,000	7,630,000
Reconciliation of the federal income tax expense at the statutory rate to the effective income tax expense
Statutory federal income tax expense	916,000	8,147,000	6,690,000
State taxes, net of federal benefit	185,000	(38,000)	713,000
State income tax apportionment adjustment		(1,137,000)	(396,000)
Extraterritorial income exclusion		(7,000)	(101,000)
Tax consequences of the sale of engines to WMES	(46,000)	1,214,000
Uncertain tax positions	97,000	195,000	113,000
Permanent differences-162(m)	385,000	737,000	406,000
Permanent differences and other	(376,000)	266,000	205,000
Total	1,161,000	9,377,000	7,630,000
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)	6.90%	(0.20%)	3.70%
State income tax apportionment adjustment (as a percent)		(4.70%)	(2.00%)
Extraterritorial income exclusion (as a percent)			(0.50%)
Tax consequences of the sale of engines to WMES (as a percent)	(1.70%)	5.10%
Uncertain tax positions (as a percent)	3.60%	0.80%	0.60%
Permanent differences-162(m) (as a percent)	14.30%	3.10%	2.10%
Permanent differences and other (as a percent)	(14.10%)	1.00%	0.90%
Effective income tax expense (as a percent)	43.00%	39.10%	38.80%
Effective tax rate reduced, related to change in California state tax		$ 1,100,000	$ 400,000