Quarterly Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 31, 2013	Sep. 27, 2013	Jun. 28, 2013	Mar. 29, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of selected quarterly financial data
Net sales	$ 288,426	$ 291,570	$ 287,965	$ 258,929	$ 286,138	$ 275,434	$ 306,141	$ 299,169	$ 1,126,890	$ 1,166,882	$ 1,273,078
Gross margin	55,797	54,843	49,801	45,462	49,164	44,483	45,992	48,339	205,903	187,978	198,783
Percent of net sales	19.30%	18.80%	17.30%	17.60%	17.20%	16.20%	15.00%	16.20%	18.30%	16.10%
Net income	$ 11,976	$ 12,440	$ 9,974	$ 7,331	$ 3,775	$ 4,992	$ 4,155	$ 6,785	$ 41,721	$ 19,707	$ 24,664
Net income per share of common stock:
Basic (in dollars per share)	$ 0.59	$ 0.61	$ 0.48	$ 0.36	$ 0.18	$ 0.24	$ 0.20	$ 0.33	$ 2.04	$ 0.96	$ 1.21
Diluted (in dollars per share)	$ 0.58	$ 0.60	$ 0.47	$ 0.35	$ 0.18	$ 0.24	$ 0.20	$ 0.33	$ 2.00	$ 0.94	$ 1.19
Cash dividends per share of common stock	$ 0.085	$ 0.085	$ 0.085	$ 0.080	$ 0.080	$ 0.080	$ 0.080	$ 0.075	$ 0.335	$ 0.315	$ 0.225
Stock price range:
High (in dollars per share)	$ 40.60	$ 39.38	$ 37.96	$ 35.19	$ 32.73	$ 33.69	$ 31.49	$ 29.81
Low (in dollars per share)	$ 26.64	$ 30.88	$ 31.69	$ 25.21	$ 25.75	$ 27.09	$ 24.58	$ 26.20