Segment Information - Financial Information by Segment (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment									3
Segment Reconciliation [Abstract]
Real estate rental revenue	$ 82,901	$ 82,502	$ 86,606	$ 84,881	$ 81,302	$ 82,819	$ 83,456	$ 77,501	$ 336,890	$ 325,078	$ 313,264
Cost of Revenue									116,230	115,650	115,013
Net operating income									220,660	209,428	198,251
Depreciation and amortization									(121,228)	(112,056)	(108,406)
General and administrative									(22,089)	(22,580)	(19,545)
Real estate impairment and casualty (gain), net									1,886	33,152	(676)
Acquisition costs									0	0	(1,178)
Interest expense									(51,144)	(47,534)	(53,126)
Other income									0	507	297
Gain on sale of real estate			2,500		24,900				2,495	24,915	101,704
Income tax benefit									0	84	615
Loss on extinguishment of debt									(1,178)	0	0
Net income	(5,688)	(5,893)	(10,750)	(3,299)	(2,337)	(2,813)	(7,847)	(6,615)	(25,630)	(19,612)	(119,288)
Less: Net loss attributable to noncontrolling interests in subsidiaries									0	(56)	(51)
Net income attributable to the controlling interests	(5,688)	$ (5,893)	$ (10,750)	$ (3,299)	(2,337)	$ (2,833)	$ (7,864)	$ (6,634)	(25,630)	(19,668)	(119,339)
Capital expenditures									72,033	64,381	58,014
Total assets	2,417,104				2,359,426				$ 2,417,104	$ 2,359,426	$ 2,253,619
Office Building [Member]
Segment Reporting Information [Line Items]
Real estate rental revenue as a percentage of total									0.53	0.52	0.53
Percentage of total income producing real estate assets									0.52	0.50
Segment Reconciliation [Abstract]
Real estate rental revenue									$ 178,474	$ 167,438	$ 165,934
Cost of Revenue									63,321	62,824	64,405
Net operating income									115,153	104,614	101,529
Capital expenditures									42,019	30,407	30,337
Total assets	1,248,673				1,203,187				$ 1,248,673	$ 1,203,187	$ 1,104,589
Multifamily [Member]
Segment Reporting Information [Line Items]
Real estate rental revenue as a percentage of total									0.28	0.29	0.27
Percentage of total income producing real estate assets									0.32	0.33
Segment Reconciliation [Abstract]
Real estate rental revenue									$ 95,194	$ 95,250	$ 85,764
Cost of Revenue									37,235	37,640	34,748
Net operating income									57,959	57,610	51,016
Capital expenditures									25,117	27,980	17,936
Total assets	792,170				767,279				$ 792,170	$ 767,279	$ 762,695
Retail [Member]
Segment Reporting Information [Line Items]
Real estate rental revenue as a percentage of total									0.19	0.19	0.20
Percentage of total income producing real estate assets									0.16	0.17
Segment Reconciliation [Abstract]
Real estate rental revenue									$ 63,222	$ 62,390	$ 61,566
Cost of Revenue									15,674	15,186	15,860
Net operating income									47,548	47,204	45,706
Capital expenditures									3,934	2,128	8,821
Total assets	341,021				346,580				341,021	346,580	352,056
Corporate And Other [Member]
Segment Reconciliation [Abstract]
Real estate rental revenue									0	0	0
Cost of Revenue									0	0	0
Net operating income									0	0	0
Capital expenditures									963	3,866	920
Total assets	$ 35,240				$ 42,380				$ 35,240	$ 42,380	$ 34,279