CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 30,335	$ (21,884)	$ 12,090
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation	89,400	66,685	52,427
Net amortization of debt premiums, discounts and issuance costs	10,740	3,626	3,420
Amortization of acquired real estate leases	197,978	94,375	56,174
Amortization of deferred leasing costs	5,973	4,833	3,802
Gain on sale of real estate	(105,131)	(20,661)	0
Loss on impairment of real estate	22,255	8,630	9,490
Loss on early extinguishment of debt	769	709	1,715
Straight line rental income	(27,507)	(10,164)	(5,582)
Other non-cash expenses, net	2,011	250	300
Loss on equity securities, net	44,007	7,552	0
Increase in carrying value of property included in discontinued operations	0	0	(619)
Equity in net losses of investees	1,259	2,269	13
Distribution of earnings from Affiliates Insurance Company	2,438	0	0
Equity in earnings of Select Income REIT included in discontinued operations	0	(20,873)	(21,584)
Net gain on issuance of shares by Select Income REIT included in discontinued operations	0	(29)	(72)
Loss on sale of Select Income REIT shares included in discontinued operations	0	15,180	0
Distributions of earnings from Select Income REIT	0	20,873	21,584
Change in assets and liabilities:
Rents receivable	12,586	5,021	(4,990)
Deferred leasing costs	(27,971)	(9,203)	(5,017)
Other assets	3,266	1,127	1,368
Accounts payable and other liabilities	(19,333)	(3,303)	11,696
Due to related persons	(27,746)	(97)	1,339
Net cash provided by operating activities	215,329	144,916	137,554
CASH FLOWS FROM INVESTING ACTIVITIES:
Real estate acquisitions	(2,905)	25,221	(1,187,012)
Real estate improvements	(62,676)	(47,500)	(45,940)
Distributions in excess of earnings from Select Income REIT	0	17,251	29,248
Distributions in excess of earnings from unconsolidated joint ventures	2,370	3,751	482
Distributions in excess of earnings from Affiliates Insurance Company	6,562	0	0
Proceeds from sale of properties, net	829,794	304,808	15,083
Proceeds from sale of Select Income REIT shares	0	435,125	0
Proceeds from sale of The RMR Group Inc. common shares, net	104,674	0	0
Net cash provided by (used in) investing activities	877,819	738,656	(1,188,139)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayment of mortgage notes payable	(12,054)	(3,708)	(11,909)
Repayment of unsecured term loans	(388,000)	(162,000)	0
Repayment of senior unsecured notes	(350,000)	0	0
Proceeds from issuance of senior notes, after discounts	0	0	297,954
Proceeds from issuance of common shares, net	0	0	493,866
Borrowings on unsecured revolving credit facility	430,000	238,000	645,000
Repayments on unsecured revolving credit facility	(605,000)	(741,000)	(235,000)
Payment of debt issuance costs	0	(3,936)	(4,644)
Repurchase of common shares	(473)	(232)	(264)
Redemption of preferred units of limited partnership	0	(20,221)	0
Preferred units of limited partnership distributions	0	(646)	0
Distributions to common shareholders	(105,868)	(170,566)	(145,209)
Net cash (used in) provided by financing activities	(1,031,395)	(864,309)	1,039,794
Increase (decrease) in cash, cash equivalents and restricted cash	61,753	19,263	(10,791)
Cash, cash equivalents and restricted cash at beginning of period	38,943	19,680	30,471
Cash, cash equivalents and restricted cash at end of period	100,696	38,943	19,680
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid	131,735	65,188	55,048
Income taxes paid	491	68	117
NON-CASH INVESTING ACTIVITIES:
Assumed working capital	0	25,170	(1,596)
Real estate and investment acquired by issuance of common shares	0	(639,809)	0
Real estate and investment acquired by assumption of debt	0	(1,719,772)	0
NON-CASH FINANCING ACTIVITIES:
Select Income REIT unsecured revolving credit facility	0	108,000	0
Assumption of mortgage notes payable	0	161,772	167,548
Assumption of senior unsecured notes	0	1,450,000	0
Preferred units of limited partnership issued	0	0	20,221
Issuance of common shares	$ 0	$ 639,809	$ 0