Income Taxes (Components of Income Before Taxes and of Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes
U.S.	$ 21,634	$ 11,319	$ 10,433
Non U.S.	2,312	1,456	1,307
Income before income taxes	23,946	12,775	11,740
Federal
Current	324	(208)	109
Deferred	8,807	4,871	3,797
Total	9,131	4,663	3,906
State
Current	14	13	179
Deferred	292	1,163	164
Total	306	1,176	343
Foreign
Current	440	476	311
Total	440	476	311
Total
Current	778	281	599
Deferred	9,099	6,034	3,961
Total	9,877	6,315	4,560
Reconciliation of the federal income tax expense at the statutory rate to the effective income tax expense
Statutory federal income tax expense	8,142	4,343	3,992
State taxes, net of federal benefit	202	776	118
Foreign tax paid	440	476	101
Tax consequences of the sale of engines to WMES		(306)	(36)
Uncertain tax positions	(40)	(195)	(101)
Permanent differences-nondeductible executive compensation	1,201	1,117	768
Permanent differences and other	(68)	104	(282)
Total	$ 9,877	$ 6,315	$ 4,560
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)	0.80%	6.10%	1.00%
Foreign tax paid (as a percent)	1.80%	3.70%	0.90%
Tax consequences of the sale of engines to WMES (as a percent)		(2.40%)	(0.30%)
Uncertain tax positions (as a percent)	(0.10%)	(1.50%)	(0.90%)
Permanent differences-162(m) (as a percent)	5.00%	8.70%	6.50%
Permanent differences and other (as a percent)	(0.30%)	0.80%	(2.40%)
Effective income tax expense (benefit) (as a percent)	41.20%	49.40%	38.80%