Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Income Statement [Abstract]
Revenues	$ 270,649	$ 245,037	$ 479,300	$ 437,850
Costs and expenses:
Operating	167,682	151,525	312,305	285,184
Selling	44,317	40,816	83,974	76,350
General and administrative	17,358	15,213	35,076	31,613
Depreciation and amortization	13,938	13,000	27,059	25,190
Gain on sale of assets, net	(2,446)	(1,176)	(3,248)	(2,151)
Costs and expenses	240,849	219,378	455,166	416,186
Income from operations	29,800	25,659	24,134	21,664
Other income (expense):
Interest expense	(1,754)	(1,072)	(3,155)	(2,329)
Interest income	101	73	179	143
Other, net	(1,052)	(1,339)	(2,714)	(2,478)
Income before income taxes	27,095	23,321	18,444	17,000
Income taxes	5,381	9,098	3,357	6,664
Net income	$ 21,714	$ 14,223	$ 15,087	$ 10,336
Net income per share:
Basic	$ 0.94	$ 0.57	$ 0.62	$ 0.41
Diluted	$ 0.89	$ 0.55	$ 0.59	$ 0.40
Weighted-average shares outstanding:
Basic	23,121	24,998	24,439	24,984
Diluted	24,307	25,985	25,561	25,998
Dividends declared per share	$ 0.025	$ 0.025	$ 0.05	$ 0.05