Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Rental income	$ 70,179	$ 64,478	$ 209,362	$ 192,150
Expenses:
Real estate taxes	8,862	7,591	24,980	22,810
Utility expenses	5,408	5,483	14,186	13,330
Other operating expenses	14,867	13,854	44,046	40,031
Depreciation and amortization	20,781	18,404	61,949	54,713
Loss on impairment of real estate	230	0	230	0
Acquisition related costs	0	147	0	363
General and administrative	3,266	3,816	12,314	11,350
Total expenses	53,414	49,295	157,705	142,597
Operating income	16,765	15,183	51,657	49,553
Dividend income	304	304	911	667
Interest income	1,715	47	1,843	63
Interest expense	(16,055)	(12,608)	(43,599)	(32,286)
(Loss) gain on early extinguishment of debt	(1,715)	0	(1,715)	104
Gain on issuance of shares by Select Income REIT	51	72	72	88
Income (loss) from continuing operations before income taxes and equity in earnings of investees	1,065	2,998	9,169	18,189
Income tax expense	(22)	(13)	(65)	(63)
Equity in earnings of investees	9,484	8,668	20,804	28,002
Income from continuing operations	10,527	11,653	29,908	46,128
Income (loss) from discontinued operations	462	(154)	173	(429)
Income (loss) before gain on sale of property	10,989	11,499	30,081	45,699
Gain on sale of property	0	79	0	79
Net income	10,989	11,578	30,081	45,778
Total assets	3,536,967		3,536,967		$ 2,385,066
Operating Segments | Investment in Real Estate
Segment Reporting Information [Line Items]
Rental income	70,179	64,478	209,362	192,150
Expenses:
Real estate taxes	8,862	7,591	24,980	22,810
Utility expenses	5,408	5,483	14,186	13,330
Other operating expenses	14,867	13,854	44,046	40,031
Depreciation and amortization	20,781	18,404	61,949	54,713
Loss on impairment of real estate	230		230
Acquisition related costs		147		363
Total expenses	50,148	45,479	145,391	131,247
Operating income	20,031	18,999	63,971	60,903
Interest income	54		148	0
Interest expense	(401)	(429)	(1,238)	(1,953)
(Loss) gain on early extinguishment of debt			(1,715)	104
Income (loss) from continuing operations before income taxes and equity in earnings of investees	19,684	18,570	61,166	59,054
Income from continuing operations	19,684	18,570	61,166	59,054
Income (loss) from discontinued operations	462	(154)	173	(429)
Income (loss) before gain on sale of property		18,416		58,625
Gain on sale of property		79		79
Net income	20,146	18,495	61,339	58,704
Total assets	1,780,753		1,780,753		1,807,560
Operating Segments | Investment in SIR
Expenses:
Gain on issuance of shares by Select Income REIT	51	72	72	88
Income (loss) from continuing operations before income taxes and equity in earnings of investees	51	72	72	88
Equity in earnings of investees	9,453	8,655	20,271	27,895
Income from continuing operations	9,504	8,727	20,343	27,983
Income (loss) before gain on sale of property		8,727		27,983
Net income	9,504	8,727	20,343	27,983
Total assets	475,265		475,265		487,708
Corporate, Non-Segment
Expenses:
Acquisition related costs				0
General and administrative	3,266	3,816	12,314	11,350
Total expenses	3,266	3,816	12,314	11,350
Operating income	(3,266)	(3,816)	(12,314)	(11,350)
Dividend income	304	304	911	667
Interest income	1,661	47	1,695	63
Interest expense	(15,654)	(12,179)	(42,361)	(30,333)
(Loss) gain on early extinguishment of debt	(1,715)
Income (loss) from continuing operations before income taxes and equity in earnings of investees	(18,670)	(15,644)	(52,069)	(40,953)
Income tax expense	(22)	(13)	(65)	(63)
Equity in earnings of investees	31	13	533	107
Income from continuing operations	(18,661)	(15,644)	(51,601)	(40,909)
Income (loss) before gain on sale of property		(15,644)		(40,909)
Net income	(18,661)	$ (15,644)	(51,601)	$ (40,909)
Total assets	$ 1,280,949		$ 1,280,949		$ 89,798