Quarterly Financial Information (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total revenue	$ 163,255,000	$ 158,443,000	$ 159,447,000	$ 163,037,000	$ 156,371,000	$ 152,350,000	$ 118,020,000	$ 116,272,000	$ 644,182,000	$ 543,013,000	$ 478,519,000
Net income (loss)	994,000	26,382,000	24,023,000	(4,786,000)	(18,752,000)	(77,991,000)	11,341,000	6,318,000	39,903,000	(71,756,000)	61,974,000
Net income (loss) attributable to common shareholders	$ 710,000	$ 22,830,000	$ 20,574,000	$ (4,190,000)	$ (16,418,000)	$ (69,831,000)	$ 11,341,000	$ 6,318,000	$ 37,325,000	$ (73,408,000)	$ 61,974,000
Earnings Per Share, Basic	$ (0.01)	$ 0.19	$ 0.17	$ (0.04)	$ (0.15)	$ (0.61)	$ 0.11	$ 0.06	$ 0.31	$ (0.70)	$ 0.62
Earnings Per Share, Diluted	$ (0.01)	$ 0.19	$ 0.17	$ (0.04)	$ (0.15)	$ (0.61)	$ 0.11	$ 0.06	$ 0.31	$ (0.70)	$ 0.62
Gains (Losses) on Sales of Investment Real Estate	$ 6,400,000		$ 33,400,000						$ 52,183,000	$ 0	$ 0
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Bargain Purchase, Reduction Of Gain			(7,600,000)		$ (3,400,000)	$ 27,800,000			(7,606,000)	24,376,000	0
Loss on extinguishment of debt			$ (4,500,000)						(5,153,000)	(701,000)	0
Transaction and other costs	15,600,000				12,600,000	104,100,000			27,706,000	127,739,000	6,476,000
Share-based compensation related to Formation Transaction					$ 14,800,000	$ 14,400,000			36,030,000	$ 29,251,000	$ 0
The Warner [Member]
Equity Method Investment, Realized Gain (Loss) on Disposal	$ 20,600,000								20,600,000
Executive Tower [Member]
Gains (Losses) on Sales of Investment Real Estate		$ 11,900,000
JP Morgan [Member]
Equity Method Investment, Realized Gain (Loss) on Disposal		$ 15,500,000							$ 15,500,000