Retirement Benefit Plans, Defined Contribution Plan (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Defined Contribution Plan [Abstract]
Total contributions for the period	$ 238,070	$ 230,313	$ 1,052,566	$ 789,727
Regular Matching Contribution [Member]
Defined Contribution Plan [Abstract]
Total contributions for the period	140,106	118,947	306,121	235,423
Transitional Credit Contribution [Member]
Defined Contribution Plan [Abstract]
Total contributions for the period	81,506	95,702	205,614	231,072
Non-discretionary Contribution [Member]
Defined Contribution Plan [Abstract]
Total contributions for the period	$ 16,458	$ 15,664	540,831	$ 323,232
Non-Union U.S. Employees [Member]
Defined Contribution Plan [Abstract]
Total contributions for the period			$ 502,617