Equity Investment in Select Income REIT - Balance Sheet Information (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Schedule of Equity Method Investments [Line Items]
Real estate properties, net	$ 2,135,589	$ 2,633,873
Acquired real estate leases, net	215,938	351,872
Properties held for sale	408,626	0
Cash and cash equivalents	9,644	16,569	$ 551,707
Rents receivable, net	55,297	61,429
Other assets, net	136,360	96,033
Total assets	3,484,425	3,703,565
Unsecured revolving credit facility	467,000	570,000
Unsecured term loan, net	548,363	547,852
Senior unsecured notes, net	945,948	944,140
Mortgage notes payable, net	176,828	183,100
Assumed real estate lease obligations, net	8,759	13,635
Other liabilities	64,868	89,440
Total shareholders' equity attributable to SIR	1,239,361	1,330,043
Total liabilities and shareholders’ equity	3,484,425	3,703,565
SIR | SIR
Schedule of Equity Method Investments [Line Items]
Real estate properties, net	3,926,606	3,905,616
Acquired real estate leases, net	433,947	477,577
Properties held for sale	15,289	5,829
Cash and cash equivalents	25,982	658,719
Rents receivable, net	131,642	127,672
Other assets, net	188,033	127,617
Total assets	4,721,499	5,303,030
Unsecured revolving credit facility	108,000	0
Industrial Logistics Properties Trust revolving credit facility	380,000	750,000
Unsecured term loan, net	0	348,870
Senior unsecured notes, net	1,430,688	1,777,425
Mortgage notes payable, net	210,624	210,785
Assumed real estate lease obligations, net	62,176	68,783
Other liabilities	150,371	155,348
Total shareholders' equity attributable to SIR	2,061,556	1,991,819
Noncontrolling interest in consolidated subsidiary	318,084	0
Total liabilities and shareholders’ equity	$ 4,721,499	$ 5,303,030