Retirement Benefit Plans, Net Periodic Benefit Cost (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Pension Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	$ 329,959	$ 317,360	$ 989,881	$ 952,078
Interest cost	776,790	791,055	2,330,373	2,373,167
Expected return on plan assets	(1,304,879)	(1,195,895)	(3,914,637)	(3,587,682)
Amortization of prior service cost	32,691	36,438	98,072	109,312
Amortization of the net loss	277,528	307,871	832,584	923,614
Net periodic benefit cost	112,089	256,829	336,273	770,489
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	2,510,000		2,510,000
Postretirement Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	9,256	6,847	27,768	20,542
Interest cost	19,290	20,206	57,871	60,620
Expected return on plan assets	(13,913)	(12,874)	(41,738)	(38,621)
Amortization of prior service cost	(1,268)	(5,361)	(3,804)	(16,083)
Amortization of the net loss	(16,397)	(19,400)	(49,193)	(58,201)
Net periodic benefit cost	(3,032)	$ (10,582)	(9,096)	$ (31,743)
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	$ 97,000		97,000
Employer contributions made			$ 8,000