Discontinued Operations - Summarized Income (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental income	$ 174,777	$ 108,717
Real estate taxes	18,392	12,964
Other operating expenses	30,136	22,837
Depreciation and amortization	77,521	44,204
General and administrative	8,723	9,606
Total expenses	147,941	102,417
Dividend income	980	304
Unrealized gain on equity securities	22,128	12,931
Interest income	248	116
Interest expense	(37,133)	(22,766)
Loss on early extinguishment of debt	(414)	0
Income before income tax expense and equity in earnings of an investee	34,737	(3,115)
Income tax expense	(483)	(32)
Equity in earnings of an investee	(235)	(577)
Net income attributed to SIR	$ 34,019	$ 6,565
Weighted average common shares outstanding (basic) (in shares)	48,031	24,760
Weighted average common shares outstanding (diluted) (in shares)	48,046	24,760
Net income attributed to SIR per common share (basic and diluted) (in dollars per share)	$ 0.71	$ 0.25
SIR
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity in earnings of an investee		$ 10,289
SIR | SIR
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental income		99,755
Tenant reimbursements and other income		20,874
Total revenues		120,629
Real estate taxes		11,788
Other operating expenses		15,282
Depreciation and amortization		34,946
General and administrative		13,941
Total expenses		75,957
Dividend income		397
Unrealized gain on equity securities		16,900
Interest income		510
Interest expense		(23,492)
Loss on early extinguishment of debt		(1,192)
Income before income tax expense and equity in earnings of an investee		37,795
Income tax expense		(160)
Equity in earnings of an investee		44
Net income		37,679
Net income allocated to noncontrolling interest		(4,479)
Net income attributed to SIR		$ 33,200
Weighted average common shares outstanding (basic) (in shares)		89,382
Weighted average common shares outstanding (diluted) (in shares)		89,390
Net income attributed to SIR per common share (basic and diluted) (in dollars per share)		$ 0.37