Retirement Benefit Plans (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Pension Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	$ 317,360	$ 270,721	$ 952,078	$ 1,612,278
Interest cost	791,055	767,625	2,373,167	2,541,968
Expected return on plan assets	(1,195,895)	(1,121,311)	(3,587,682)	(3,603,483)
Amortization of prior service cost	36,438	50,143	109,312	150,427
Amortization of the net loss	307,871	277,469	923,614	1,319,617
Net periodic benefit cost	256,829	244,647	770,489	2,020,807
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	700,000		700,000
Employer contributions made			322,000
Postretirement Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	6,847	7,325	20,542	21,975
Interest cost	20,206	23,718	60,620	71,154
Expected return on plan assets	(12,874)	(11,883)	(38,621)	(35,649)
Amortization of prior service cost	(5,361)	(5,973)	(16,083)	(17,918)
Amortization of the net loss	(19,400)	(23,480)	(58,201)	(70,441)
Net periodic benefit cost	(10,582)	$ (10,293)	(31,743)	$ (30,879)
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	$ 140,000		140,000
Employer contributions made			109,000
Change in Accounting Method Accounted for as Change in Estimate [Member]
Change in Accounting Estimate [Line Items]
Reduction in pension expense			$ (406,000)