Indebtedness	9 Months Ended
Indebtedness	Sep. 30, 2019
Debt Disclosure [Abstract]
Indebtedness	Indebtedness Our principal debt obligations at September 30, 2019 were: (1) $210,000 of outstanding borrowings under our $750,000 unsecured revolving credit facility; (2) $2,060,000 aggregate outstanding principal amount of senior unsecured notes; and (3) $327,262 aggregate outstanding principal amount of mortgage notes, including one mortgage note with an outstanding principal balance of $13,236 classified in liabilities of properties held for sale in our condensed consolidated balance sheet. Our $750,000 revolving credit facility is governed by a credit agreement, or our credit agreement, with a syndicate of institutional lenders that includes a feature under which the maximum aggregate borrowing availability may be increased to up to $1,950,000 in certain circumstances. Our $750,000 revolving credit facility is available for general business purposes, including acquisitions. The maturity date of our revolving credit facility is January 31, 2023 and, subject to our payment of an extension fee and meeting certain other conditions, we have the option to extend the stated maturity date of our revolving credit facility by two additional six month periods. We can borrow, repay and reborrow funds available under our revolving credit facility until maturity and no principal repayment is due until maturity. We are required to pay interest at a rate of LIBOR plus a premium, which was 110 basis points per annum at September 30, 2019, on the amount outstanding under our revolving credit facility. We also pay a facility fee on the total amount of lending commitments under our revolving credit facility, which was 25 basis points per annum at September 30, 2019. Both the interest rate premium and the facility fee are subject to adjustment based upon changes to our credit ratings. As of September 30, 2019 and December 31, 2018, the annual interest rate payable on borrowings under our revolving credit facility was 3.0% and 3.6%, respectively. The weighted average annual interest rate for borrowings under our revolving credit facility was 3.3% and 3.2% for the three months ended September 30, 2019 and 2018, respectively, and 3.4% and 3.0% for the nine months ended September 30, 2019 and 2018, respectively. As of September 30, 2019 and October 31, 2019, we had $210,000 and $185,000, respectively, outstanding under our revolving credit facility, and $540,000 and $565,000, respectively, available for borrowing under our revolving credit facility. The remaining outstanding balance of our $300,000 term loan, which was scheduled to mature on March 31, 2020, was repaid in full on August 23, 2019, without penalty, using cash on hand, proceeds from the sale of properties and the proceeds from our sale of our 2,801,060 shares of class A common stock of The RMR Group Inc., or RMR Inc., as described in Note 11. The weighted average annual interest rate under this term loan was 3.7% and 3.5% for the period from July 1, 2019 to August 23, 2019 and the three months ended September 30, 2018, respectively, and 3.9% and 3.3% for the period from January 1, 2019 to August 23, 2019 and the nine months ended September 30, 2018, respectively. Our $250,000 term loan, which was scheduled to mature on March 31, 2022 and had a principal balance of $88,000 as of December 31, 2018, was repaid in full on February 11, 2019, without penalty, using proceeds from the sale of a property portfolio. The weighted average annual interest rate under this term loan was 4.3% for the period from January 1, 2019 to February 11, 2019, and 3.9% and 3.7% for the three and nine months ended September 30, 2018, respectively. As a result of the principal payments of our term loans, we recognized a loss on early extinguishment of debt of $158 and $643 for the three and nine months ended September 30, 2019, respectively, to write off unamortized debt issuance costs. On July 15, 2019, we redeemed, at par plus accrued interest, all $350,000 of our 3.75% senior unsecured notes that had a maturity date in August 2019 using cash on hand and borrowings under our revolving credit facility. As a result of the redemption of our 3.75% senior unsecured notes, we recognized a loss on early extinguishment of debt of $126 for the three and nine months ended September 30, 2019 to write off unamortized debt issuance costs and discounts. Our credit agreement and senior unsecured notes indentures and their supplements provide for acceleration of payment of all amounts due thereunder upon the occurrence and continuation of certain events of default, such as, in the case of our credit agreement, a change of control of us, which includes The RMR Group LLC, or RMR LLC, ceasing to act as our business and property manager. Our credit agreement and senior unsecured notes indentures and their supplements also contain covenants, including those that restrict our ability to incur debts, require us to maintain certain financial ratios and, in the case of our credit agreement, restrict our ability to make distributions under certain circumstances. We believe we were in compliance with the terms and conditions of the respective covenants under our credit agreement and senior unsecured notes indentures and their supplements at September 30, 2019. On March 1, 2019, we repaid at maturity, at par plus accrued interest, a mortgage note secured by one property with an outstanding principal balance of $7,890 using cash on hand. At September 30, 2019, 11 of our consolidated properties with an aggregate net book value of $601,003 were encumbered by mortgage notes with an aggregate principal amount of $327,262, including one mortgage note with an outstanding principal balance of $13,236 classified in liabilities of properties held for sale in our condensed consolidated balance sheet. Our mortgage notes are non-recourse, subject to certain limited exceptions and do not contain any material financial covenants.