Debt - (Details) - USD ($)	1 Months Ended	9 Months Ended
	Oct. 31, 2015	Sep. 29, 2017	Sep. 30, 2016	Dec. 31, 2016
Line of Credit Facility [Line Items]
Long-term debt		$ 0		$ 4,725,000
Maximum amount outstanding		4,200,000	$ 4,600,000
Average amount outstanding		$ 2,300,000	$ 2,000,000
Weighted-average interest rate		2.90%	3.50%
Debt covenants, Maximum leverage ratio		275.00%
Debt covenants, Minimum tangible net worth		$ 48,600,000
Debt covenants, Maximum capital expenditures		$ 5,000,000
Leverage ratio		0.0
Tangible net worth		$ 76,900,000
Capital expenditures		$ 1,300,000
Unsecured Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 40,000,000
Line of credit facility, expiration date		2018-10
Life Insurance Loan Capacity [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 17,500,000
Prime Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Prime Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%