Equity Investment in Select Income REIT - Balance Sheet Information (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Real estate properties, net	$ 2,583,404	$ 2,633,873
Acquired real estate leases, net	323,710	351,872
Cash and cash equivalents	17,380	16,569	$ 12,808
Rents receivable, net	65,539	61,429
Other assets, net	106,234	96,033
Total assets	3,655,624	3,703,565	$ 3,703,565
Unsecured revolving credit facility	570,000	570,000
Unsecured term loan, net	548,022	547,852
Senior unsecured notes, net	944,743	944,140
Mortgage notes payable, net	182,083	183,100
Assumed real estate lease obligations, net	12,480	13,635
Other liabilities	74,623	89,440
Total shareholders' equity attributable to SIR	1,294,358	1,330,043
Total liabilities and shareholders’ equity	3,655,624	3,703,565
SIR | SIR
Schedule of Equity Method Investments [Line Items]
Real estate properties, net	3,888,100	3,905,616
Acquired real estate leases, net	461,577	477,577
Properties held for sale	5,829	5,829
Cash and cash equivalents	30,884	658,719
Rents receivable, net	131,445	127,672
Other assets, net	151,174	127,617
Total assets	4,669,009	5,303,030
Unsecured revolving credit facility	107,000	0
Industrial Logistics Properties Trust revolving credit facility	302,000	750,000
Unsecured term loan, net	0	348,870
Senior unsecured notes, net	1,428,571	1,777,425
Mortgage notes payable, net	210,749	210,785
Assumed real estate lease obligations, net	66,577	68,783
Other liabilities	125,668	155,348
Total shareholders' equity attributable to SIR	2,110,595	1,991,819
Noncontrolling interest in consolidated subsidiary	317,849	0
Total liabilities and shareholders’ equity	$ 4,669,009	$ 5,303,030