Condensed Consolidated Statements of Operations shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jul. 01, 2017 USD ($) $ / shares shares	Jul. 02, 2016 USD ($) $ / shares shares	Jul. 01, 2017 USD ($) $ / shares shares	Jul. 02, 2016 USD ($) $ / shares shares
Income Statement [Abstract]
Revenues		$ 245,037	$ 224,763	$ 437,850	$ 405,596
Costs and expenses:
Operating		151,525	137,132	285,184	260,305
Selling		40,816	36,859	76,350	71,189
General and administrative		15,560	14,675	32,307	31,814
Depreciation and amortization		13,000	12,290	25,190	23,631
Gain on sale of assets, net		(1,176)	(479)	(2,151)	(509)
Costs and expenses		219,725	200,477	416,880	386,430
Income from operations		25,312	24,286	20,970	19,166
Other income (expense):
Interest expense		(1,072)	(1,062)	(2,329)	(2,027)
Interest income		73	60	143	128
Other, net		(992)	(1,156)	(1,784)	(1,755)
Income before income taxes		23,321	22,128	17,000	15,512
Income taxes		9,098	8,819	6,664	6,391
Net income		$ 14,223	$ 13,309	$ 10,336	$ 9,121
Net income per share:
Basic | $ / shares	[1]	$ 0.57	$ 0.52	$ 0.41	$ 0.35
Diluted | $ / shares	[1]	$ 0.55	$ 0.50	$ 0.40	$ 0.34
Weighted-average shares outstanding:
Basic | shares	[1]	24,998	25,740	24,984	25,958
Diluted | shares	[1]	25,985	26,698	25,998	26,968
Dividends declared per share | $ / shares	[1]	$ 0.025	$ 0.025	$ 0.050	$ 0.050
Stock split, conversion ratio				2

[1] Adjusted for two-for-one stock split