Retirement Benefit Plans (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Pension Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	$ 329,960	$ 317,360
Interest cost	776,792	791,057
Expected return on plan assets	(1,304,880)	(1,195,895)
Amortization of prior service cost	32,691	36,438
Amortization of the net loss	277,528	307,870
Net periodic benefit cost	112,091	256,830
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	510,000
Employer contributions made	0
Postretirement Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	9,256	6,847
Interest cost	19,290	20,207
Expected return on plan assets	(13,913)	(12,874)
Amortization of prior service cost	(1,268)	(5,361)
Amortization of the net loss	(16,398)	(19,400)
Net periodic benefit cost	(3,033)	$ (10,581)
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	105,000
Employer contributions made	$ 36,000