Earnings Per Share Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 31, 2015	Oct. 03, 2015	Jul. 04, 2015	Apr. 04, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 5,022	$ 8,141	$ 13,309	$ (4,188)	$ 1,220	$ 8,174	$ 15,932	$ (3,528)	$ 22,284	$ 21,798	$ 23,169
Weighted-average shares, basic
Outstanding									12,689,300	13,029,368	13,337,198
Partially-paid share subscriptions									416,720	436,081	484,025
Basic weighted-average shares									13,106,020	13,465,449	13,821,223
Weighted-average shares, diluted
Exercise of stock subscription purchase rights									71,373	67,714	54,824
Exercise of stock options and awards									446,284	444,127	362,229
Diluted weighted-average shares									13,623,677	13,977,290	14,238,276
Earnings per share--basic	$ 0.37	$ 0.63	$ 1.03	$ (0.33)	$ 0.10	$ 0.58	$ 1.21	$ (0.27)	$ 1.70	$ 1.62	$ 1.68
Earnings per share--diluted	$ 0.36	$ 0.61	$ 1.00	$ (0.33)	$ 0.11	$ 0.55	$ 1.17	$ (0.27)	$ 1.64	$ 1.56	$ 1.63