Per Share Amounts and Common Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 03, 2015	Sep. 27, 2014	Oct. 03, 2015	Sep. 27, 2014	May. 19, 2015	Dec. 31, 2014
Equity [Abstract]
Net income	$ 8,174	$ 9,657	$ 20,578	$ 19,692
Weighted-average shares outstanding, basic	14,032,000	13,307,000	13,107,000	13,382,000
Weighted-average shares, partially-paid share subscriptions	112,000	121,000	335,000	363,000
Basic weighted average shares	14,144,000	13,428,000	13,442,000	13,745,000
Incremental shares from assumed exercise of stock subscription purchase rights	82,000	77,000	68,000	55,000
Incremental shares from assumed exercise of stock options and awards	559,000	394,000	452,000	367,000
Diluted weighted-average shares	14,785,000	13,899,000	13,962,000	14,167,000
Net income per share basic	$ 0.58	$ 0.72	$ 1.53	$ 1.43
Net income per share diluted	$ 0.55	$ 0.69	$ 1.47	$ 1.39
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2015			13,164,933
Shares purchased			(526,995)
Shares sold			210,156
Stock subscription offering -- cash purchases			30,954
Options and awards exercised			51,606
Change in shares outstanding			(234,279)
Shares outstanding at October 3, 2015	12,930,654		12,930,654
Common shares, par value	$ 1.00		$ 1.00			$ 1.00
Common shares, authorized	48,000,000		48,000,000		48,000,000	24,000,000
Preferred shares, authorized	4,000,000		4,000,000
Preferred shares, issued	0		0
Employee and director options exercisable	397,345		397,345
Partially-paid subscriptions	447,723		447,723
Purchase rights outstanding	182,696		182,696