Indebtedness	9 Months Ended
Sep. 30, 2018
Debt Disclosure [Abstract]
Indebtedness	Indebtedness Our principal debt obligations at September 30, 2018 were: (1) $467,000 of outstanding borrowings under our $750,000 unsecured revolving credit facility; (2) $550,000 aggregate outstanding principal amount of unsecured term loans; (3) $960,000 aggregate outstanding principal amount of senior unsecured notes; and (4) $180,416 aggregate outstanding principal amount of mortgage notes. Our $750,000 revolving credit facility, our $300,000 term loan and our $250,000 term loan are governed by a credit agreement, or our credit agreement, with a syndicate of institutional lenders that includes a number of features common to all of these credit arrangements. Our credit agreement also includes a feature under which the maximum aggregate borrowing availability may be increased to up to $2,500,000 on a combined basis 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, 2019 and, subject to the payment of an extension fee and meeting other conditions, we have an option to extend the stated maturity date of our revolving credit facility by one year to January 31, 2020. 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 125 basis points per annum at September 30, 2018, on borrowings 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, 2018. Both the interest rate premium and the facility fee are subject to adjustment based upon changes to our credit ratings. As of September 30, 2018, the annual interest rate payable on borrowings under our revolving credit facility was 3.4% and the weighted average annual interest rate for borrowings under our revolving credit facility was 3.2% and 2.4% for the three months ended September 30, 2018 and 2017, respectively, and 3.0% and 2.2% for the nine months ended September 30, 2018 and 2017, respectively. As of September 30, 2018 and October 30, 2018, we had $467,000 and $32,000 outstanding under our revolving credit facility. Our $300,000 term loan, which matures on March 31, 2020, is prepayable without penalty at any time. We are required to pay interest at a rate of LIBOR plus a premium, which was 140 basis points per annum at September 30, 2018, on the amount outstanding under our $300,000 term loan. The interest rate premium is subject to adjustment based upon changes to our credit ratings. As of September 30, 2018, the annual interest rate for the amount outstanding under our $300,000 term loan was 3.6%. The weighted average annual interest rate under our $300,000 term loan was 3.5% and 2.6% for the three months ended September 30, 2018 and 2017, respectively, and 3.3% and 2.4% for the nine months ended September 30, 2018 and 2017, respectively. Our $250,000 term loan, which matures on March 31, 2022, is prepayable without penalty at any time. We are required to pay interest at a rate of LIBOR plus a premium, which was 180 basis points per annum as of September 30, 2018, on the amount outstanding under our $250,000 term loan. The interest rate premium is subject to adjustment based upon changes to our credit ratings. As of September 30, 2018, the annual interest rate for the amount outstanding under our $250,000 term loan was 4.0%. The weighted average annual interest rate under our $250,000 term loan was 3.9% and 3.0% for the three months ended September 30, 2018 and 2017, respectively, and 3.7% and 2.8% for the nine months ended September 30, 2018 and 2017, respectively. 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 RMR LLC ceasing to act as our business and property manager. Our credit agreement and our senior unsecured notes indentures and their supplements also contain a number of covenants, including covenants 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, 2018. At September 30, 2018, eight of our consolidated properties (eight buildings) with an aggregate net book value of $417,842 were encumbered by eight mortgages for an aggregate principal amount of $180,416. Our mortgage notes are non-recourse, subject to certain limited exceptions and do not contain any material financial covenants.

Indebtedness

Our principal debt obligations at September 30, 2018 were: (1) $467,000 of outstanding borrowings under our $750,000 unsecured revolving credit facility; (2) $550,000 aggregate outstanding principal amount of unsecured term loans; (3) $960,000 aggregate outstanding principal amount of senior unsecured notes; and (4) $180,416 aggregate outstanding principal amount of mortgage notes.

Our $750,000 revolving credit facility, our $300,000 term loan and our $250,000 term loan are governed by a credit agreement, or our credit agreement, with a syndicate of institutional lenders that includes a number of features common to all of these credit arrangements. Our credit agreement also includes a feature under which the maximum aggregate borrowing availability may be increased to up to $2,500,000 on a combined basis 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, 2019 and, subject to the payment of an extension fee and meeting other conditions, we have an option to extend the stated maturity date of our revolving credit facility by one year to January 31, 2020. 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 125 basis points per annum at September 30, 2018, on borrowings 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, 2018. Both the interest rate premium and the facility fee are subject to adjustment based upon changes to our credit ratings. As of September 30, 2018, the annual interest rate payable on borrowings under our revolving credit facility was 3.4% and the weighted average annual interest rate for borrowings under our revolving credit facility was 3.2% and 2.4% for the three months ended September 30, 2018 and 2017, respectively, and 3.0% and 2.2% for the nine months ended September 30, 2018 and 2017, respectively. As of September 30, 2018 and October 30, 2018, we had $467,000 and $32,000 outstanding under our revolving credit facility.

Our $300,000 term loan, which matures on March 31, 2020, is prepayable without penalty at any time. We are required to pay interest at a rate of LIBOR plus a premium, which was 140 basis points per annum at September 30, 2018, on the amount outstanding under our $300,000 term loan. The interest rate premium is subject to adjustment based upon changes to our credit ratings. As of September 30, 2018, the annual interest rate for the amount outstanding under our $300,000 term loan was 3.6%. The weighted average annual interest rate under our $300,000 term loan was 3.5% and 2.6% for the three months ended September 30, 2018 and 2017, respectively, and 3.3% and 2.4% for the nine months ended September 30, 2018 and 2017, respectively.

Our $250,000 term loan, which matures on March 31, 2022, is prepayable without penalty at any time. We are required to pay interest at a rate of LIBOR plus a premium, which was 180 basis points per annum as of September 30, 2018, on the amount outstanding under our $250,000 term loan. The interest rate premium is subject to adjustment based upon changes to our credit ratings. As of September 30, 2018, the annual interest rate for the amount outstanding under our $250,000 term loan was 4.0%. The weighted average annual interest rate under our $250,000 term loan was 3.9% and 3.0% for the three months ended September 30, 2018 and 2017, respectively, and 3.7% and 2.8% for the nine months ended September 30, 2018 and 2017, respectively.

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 RMR LLC ceasing to act as our business and property manager. Our credit agreement and our senior unsecured notes indentures and their supplements also contain a number of covenants, including covenants 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, 2018.

At September 30, 2018, eight of our consolidated properties (eight buildings) with an aggregate net book value of $417,842 were encumbered by eight mortgages for an aggregate principal amount of $180,416. Our mortgage notes are non-recourse, subject to certain limited exceptions and do not contain any material financial covenants.