Subsequent Event (Details) $ / shares in Units, ft² in Thousands, $ in Millions			3 Months Ended								12 Months Ended
	Feb. 21, 2018 $ / shares	Jan. 30, 2018 USD ($) ft²	Dec. 31, 2017 $ / shares	Sep. 24, 2017 $ / shares	Jun. 25, 2017 $ / shares	Mar. 26, 2017 $ / shares	Dec. 25, 2016 $ / shares	Sep. 25, 2016 $ / shares	Jun. 26, 2016 $ / shares	Mar. 27, 2016 $ / shares	Dec. 31, 2017 $ / shares	Dec. 25, 2016 $ / shares	Dec. 27, 2015 $ / shares
Subsequent Event [Line Items]
Dividends approved (in usd per share)			$ 0.04	$ 0.08	$ 0.00	$ 0.04	$ 0.04	$ 0.08	$ 0.00	$ 0.04	$ 0.16	$ 0.16	$ 0.16
Subsequent Event [Member]
Subsequent Event [Line Items]
Rentable square footage | ft²		750
Sale leaseback transaction, sale price for the Condo Interest | $		$ 225
Sale leaseback purchase option price | $		$ 250
Sale leaseback financing, amortization period		10 years
Class B Common Stock | Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends approved (in usd per share)	$ 0.04
Class A Common Stock | Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends approved (in usd per share)	$ 0.04