Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 26, 2018	Dec. 26, 2017
Condensed Consolidated Balance Sheets
Receivables, allowance for doubtful accounts (in dollars)	$ 60	$ 43
Property and equipment, accumulated depreciation (in dollars)	564,899	527,710
Intangible assets, accumulated amortization (in dollars)	$ 13,046	$ 12,675
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	71,474,209	71,168,897
Common stock, shares outstanding	71,474,209	71,168,897