Retirement Benefit Plans (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Pension Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	$ 329,901	$ 317,358	$ 659,922	$ 634,718
Interest cost	776,791	791,055	1,553,583	1,582,112
Expected return on plan assets	(1,304,878)	(1,195,892)	(2,609,758)	(2,391,787)
Amortization of prior service cost	32,690	36,436	65,381	72,874
Amortization of the net loss	277,528	307,873	555,056	615,743
Net periodic benefit cost	112,032	256,830	224,184	513,660
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	510,000		510,000
Employer contributions made			0
Postretirement Benefits [Member]
Components of the net periodic benefit cost [Abstract]
Service cost	9,256	6,848	18,512	13,695
Interest cost	19,291	20,207	38,581	40,414
Expected return on plan assets	(13,912)	(12,873)	(27,825)	(25,747)
Amortization of prior service cost	(1,268)	(5,361)	(2,536)	(10,722)
Amortization of the net loss	(16,398)	(19,401)	(32,796)	(38,801)
Net periodic benefit cost	(3,031)	$ (10,580)	(6,064)	$ (21,161)
Additional information [Abstract]
Contributions required by the Company in defined benefit plan	$ 105,000		105,000
Employer contributions made			$ 64,000