Other Liabilities (Summary Of Other Liabilities Including Pension) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Aug. 29, 2014
Other Liabilities [Abstract]
Liability for demolition costs	$ 2,844	$ 2,928
Accrued pension	684	684
Security deposit payable	132	132
Finance lease liabilities	49	49
Other	33	33
Other current liabilities	3,742	3,826
Lease make-good provision	7,416	7,408
Accrued pension	3,940	4,048	$ 7,500
Deferred rent liability	2,827	2,897
Environmental reserve	1,656	1,656
Lease liability	5,900	5,900
Acquired leases	29	31
Finance lease liabilities	56	69
Other		8
Other non-current liabilities	$ 21,824	$ 22,017