Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015	Jun. 28, 2014	Jul. 04, 2015	Jun. 28, 2014
Income Statement [Abstract]
Revenues	$ 224,773	$ 213,183	$ 399,065	$ 370,570
Costs and expenses:
Operating	137,341	130,283	257,199	239,514
Selling	34,914	35,813	67,570	64,872
General and administrative	13,534	12,905	28,666	26,804
Depreciation and amortization	11,607	10,468	22,268	20,368
Gain on sale of assets, net	(419)	(101)	(449)	(78)
Costs and expenses	196,977	189,368	375,254	351,480
Income from operations	27,796	23,815	23,811	19,090
Other income (expense):
Interest expense	(900)	(706)	(1,690)	(1,425)
Interest income	59	76	122	145
Other, net	(881)	(500)	(1,708)	(1,305)
Income before income taxes	26,074	22,685	20,535	16,505
Income taxes	10,142	8,639	8,131	6,470
Net income	$ 15,932	$ 14,046	$ 12,404	$ 10,035
Net income per share:
Basic	$ 1.21	$ 1.04	$ 0.93	$ 0.73
Diluted	$ 1.17	$ 1.01	$ 0.90	$ 0.71
Weighted-average shares outstanding:
Basic	13,214	13,486	13,375	13,671
Diluted	13,665	13,880	13,835	14,070
Dividends declared per share	$ 0.05	$ 0.045	$ 0.100	$ 0.090