Equity Investment in Select Income REIT - Income Statement Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 69,887	$ 64,061	$ 139,183	$ 127,672
Real estate taxes	7,941	7,566	16,118	15,219
Other operating expenses	15,187	13,266	29,179	26,177
Depreciation and amortization	20,663	17,985	41,168	36,309
Acquisition related costs	0	64	0	216
General and administrative	5,086	4,008	9,048	7,534
Total expenses	53,049	46,562	104,291	93,302
Operating income	16,838	17,499	34,892	34,370
Dividend income	303	363	607	363
Interest expense	(13,963)	(10,314)	(27,544)	(19,678)
Income from continuing operations before income taxes and equity in earnings of investees	3,266	7,574	8,104	15,191
Income tax expense	(25)	(35)	(43)	(50)
Equity in earnings of an investee	$ 8,581	$ 9,400	$ 11,320	$ 19,334
Weighted average common shares outstanding (basic) (in shares)	71,088	71,038	71,083	71,034
Weighted average common shares outstanding (diluted) (in shares)	71,119	71,061	71,109	71,046
Net income attributed to SIR per common share (basic and diluted) (in dollars per share)	$ 0.16	$ 0.24	$ 0.27	$ 0.48
SIR
Schedule of Equity Method Investments [Line Items]
Equity in earnings of an investee	$ 8,207	$ 9,383	$ 10,818	$ 19,240
SIR | SIR
Schedule of Equity Method Investments [Line Items]
Rental income	97,041	96,615	194,385	194,475
Tenant reimbursements and other income	18,829	18,289	37,779	37,661
Total revenues	115,870	114,904	232,164	232,136
Real estate taxes	10,836	10,522	21,679	20,810
Other operating expenses	13,523	12,635	26,390	25,593
Depreciation and amortization	34,317	33,405	68,057	66,874
Acquisition related costs	0	0	0	58
General and administrative	8,181	7,374	23,069	14,350
Write-off of straight line rents receivable, net	0	0	12,517	0
Loss on asset impairment	0	0	4,047	0
Loss on impairment of real estate assets	229	0	229	0
Total expenses	67,086	63,936	155,988	127,685
Operating income	48,784	50,968	76,176	104,451
Dividend income	396	475	793	475
Interest expense	(22,808)	(20,584)	(43,895)	(41,193)
Income from continuing operations before income taxes and equity in earnings of investees	26,372	30,859	33,074	63,733
Income tax expense	(85)	(124)	(187)	(263)
Equity in earnings of an investee	374	17	502	94
Net income	26,661	30,752	33,389	63,564
Net income allocated to noncontrolling interest	0	0	0	(33)
Net income attributed to SIR	$ 26,661	$ 30,752	$ 33,389	$ 63,531
Weighted average common shares outstanding (basic) (in shares)	89,338	89,292	89,334	89,289
Weighted average common shares outstanding (diluted) (in shares)	89,362	89,315	89,356	89,306
Net income attributed to SIR per common share (basic and diluted) (in dollars per share)	$ 0.30	$ 0.34	$ 0.37	$ 0.71