Debt (Union Square Construction Financing) (Narrative) (Details) $ in Thousands		6 Months Ended		12 Months Ended
	Dec. 29, 2016 USD ($) loan	Jun. 30, 2018 USD ($)		Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Contractual facility		$ 270,746		$ 271,732
Union Square Construction Financing [Member]
Debt Instrument [Line Items]
Contractual facility	$ 57,500	57,500	[1]	$ 57,500	[2]
Advanced-to-Date		19,888
Facility Limit		57,500
Union Square Construction Financing [Member] | Non-Mezzanine Loan [Member]
Debt Instrument [Line Items]
Advanced-to-Date		4,400
Union Square Construction Financing [Member] | Senior Loan [Member]
Debt Instrument [Line Items]
Advanced-to-Date		7,500
Union Square Construction Financing [Member] | Bank Of The Ozarks [Member]
Debt Instrument [Line Items]
Contractual facility	$ 50,000
Number of loan tranches | loan	3
Advanced-to-Date	$ 8,000
Facility Limit	8,000
Union Square Construction Financing [Member] | Tammany Mezz Investor, LLC [Member] | Mezzanine Loan [Member]
Debt Instrument [Line Items]
Contractual facility	$ 7,500
Advanced-to-Date		7,500
Facility Limit		$ 7,500

[1] The term loan for our Cinema 1,2,3 Theatre was refinanced during the third quarter of 2016 with Valley National Bank. The term loan, which is collateralized by our new U.S Corporate Headquarters office building, was obtained with Citizens Asset Finance Inc. The loan for our Minetta and Orpheum Theatres was obtained from Santander Bank. In December 2016, we completed the negotiation of the construction financing for our Union Square redevelopment project, $8.0 million of which was advanced from the total construction loan limit of $57.5 million on December 29, 2016. As of June 30, 2018 an additional $11.9 million had been advanced.

[2] The term loan for our Cinema 1,2,3 Theatre was refinanced during the third quarter of 2016 with Valley National Bank. The term loan, which is collateralized by our new U.S Corporate Headquarters office building, was obtained with Citizens Asset Finance, Inc.. The loan for our Minetta & Orpheum Theatres was obtained from Santander Bank. In December 2016, we completed the negotiation of the construction financing for our Union Square redevelopment project, $8.0 million of which was advanced from the total construction loan limit of $57.5 million on December 29, 2016. As of December 31, 2017 no further advances had been made under this financing agreement.