Schedule III: Real Estate and Accumulated Depreciation (Rollforward of Real Estate and Accumulated Deprecation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REAL ESTATE:
Balance at beginning of period	$ 1,027,691	$ 1,037,368	$ 1,033,551
Subtotal real estate	1,041,342	1,041,281	1,037,368
Less: Fully depreciated assets	0	(13,590)	0
Balance at end of the period	1,041,342	1,027,691	1,037,368
ACCUMULATED DEPRECIATION:
Balance at beginning of period	297,421	283,044	252,737
Additions charged to operating expenses	27,078	27,967	30,307
Subtotal of accumulated depreciation	324,499	311,011	283,044
Less: Fully depreciated assets	0	(13,590)	0
Balance at end of the period	324,499	297,421	283,044
Land
REAL ESTATE:
Changes during the period	0	0	0
Buildings and leasehold improvements
REAL ESTATE:
Changes during the period	5,579	3,218	3,046
Development and construction in progress
REAL ESTATE:
Changes during the period	$ 8,072	$ 695	$ 771