Income Taxes - Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 25, 2016
Income Taxes
Balance at the beginning of the period	$ 4,827,000	$ 5,670,000
Additions for tax positions of current year	134,000	126,000
Additions for tax positions of prior years		183,000
Reductions for tax positions of prior years	(2,862,000)
Reductions for lapse of statute of limitations	(71,000)	(1,152,000)
Balance at the end of the period	2,028,000	4,827,000
Interest benefit included in income tax expense	416,000	278,000
Income tax expense, accrued interest and penalties	$ 124,000	$ 544,000