Unaudited Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,988	$ 1,772
Property and equipment, accumulated depreciation	258,769	231,319
Intangible assets, accumulated amortization	$ 75,055	$ 62,624
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	30,970,452	30,965,452
Common stock, shares outstanding	27,282,230	28,378,827
Treasury stock, shares	3,688,222	2,586,625
Interest rate swaps, income taxes	$ 60	$ 94