Debt (Details Textual)				12 Months Ended
	Oct. 01, 2020 USD ($)	Jan. 01, 2020 USD ($)	Nov. 30, 2018 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	May 07, 2020 USD ($)
Short-term Debt [Line Items]
Long-term debt				$ 12,748,000	$ 82,870,000
Unamortized debt issuance costs				1,100,000
Cash proceeds from termination of interest rate derivatives				0	0	$ 544,000
Value of contributed shares				3,037,000	2,978,000	2,960,000
Contract costs				600,000	600,000
Pre-tax gain on sale of business				6,064,000	12,126,000	0
IC Axon [Member]
Short-term Debt [Line Items]
Pre-tax gain on sale of business	$ 5.0
Alternative Fuels Division
Short-term Debt [Line Items]
Pre-tax gain on sale of business		$ 1,100,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | IC Axon [Member]
Short-term Debt [Line Items]
Pre-tax gain on sale of business	5,000,000.0
Direct selling costs	$ 300,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Alternative Fuels Division
Short-term Debt [Line Items]
Pre-tax gain on sale of business		1,100,000
Direct selling costs		$ 1,300,000
GP Retirement Savings Plan [Member] | Domestic Plan [Member]
Short-term Debt [Line Items]
Value of contributed shares				3,000,000.0	$ 3,000,000.0	$ 3,000,000.0
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Available borrowing capacity				$ 79,900,000
Interest rate during period (percent)				2.60%	4.50%
Credit Agreement [Member] | Base Rate [Member] | Minimum [Member]
Short-term Debt [Line Items]
Spread on variable rate (percent)			0.25%
Credit Agreement [Member] | Base Rate [Member] | Maximum [Member]
Short-term Debt [Line Items]
Spread on variable rate (percent)			1.25%
Credit Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Spread on variable rate (percent)			1.00%
Credit Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Short-term Debt [Line Items]
Spread on variable rate (percent)			1.25%
Credit Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Short-term Debt [Line Items]
Spread on variable rate (percent)			2.25%
Credit Agreement [Member] | Overnight Bank Funding Rate [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity			$ 200,000,000
Spread on variable rate (percent)			0.50%
Credit Agreement [Member] | Revolving Credit Facility [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity			$ 200,000,000				$ 140,000,000
Debt Instrument, Covenant, Leverage Ratio				0.5
Debt Instrument, Covenant, Minimum Interest Expense Coverage				9.1			3.0
Credit Agreement [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | Fiscal Quarters Through March 31, 2021
Short-term Debt [Line Items]
Debt Instrument, Covenant, Leverage Ratio							3.0
Credit Agreement [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | Minimum [Member] | Fiscal Quarters Through December 31, 2020
Short-term Debt [Line Items]
Debt Instrument, Covenant, Leverage Ratio							3.0
Credit Agreement [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | Maximum [Member] | Fiscal Quarters Through December 31, 2020
Short-term Debt [Line Items]
Debt Instrument, Covenant, Leverage Ratio							3.75
Credit Agreement [Member] | Revolving Credit Facility [Member] | Foreign Line of Credit [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity			20,000,000
Credit Agreement [Member] | Revolving Credit Facility [Member] | Accordion Feature [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity			100,000,000
Credit Agreement [Member] | Revolving Credit Facility [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity			20,000,000
Credit Agreement [Member] | Revolving Credit Facility [Member] | Swing Line Loan Credit [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity			$ 20,000,000