Indebtedness	3 Months Ended
Mar. 31, 2017
Debt Disclosure [Abstract]
Indebtedness	Indebtedness Our principal debt obligations at March 31, 2017 were: (1) outstanding borrowings under our $1,000,000 unsecured revolving credit facility; (2) six public issuances of senior unsecured notes, including: (a) $400,000 principal amount at an annual interest rate of 3.25% due 2019, (b) $200,000 principal amount at an annual interest rate of 6.75% due 2020, (c) $300,000 principal amount at an annual interest rate of 6.75% due 2021, (d) $250,000 principal amount at an annual interest rate of 4.75% due 2024, (e) $350,000 principal amount at an annual interest rate of 5.625% due 2042 and (f) $250,000 principal amount at an annual interest rate of 6.25% due 2046; (3) our $350,000 principal amount term loan due 2020; (4) our $200,000 principal amount term loan due 2022; and (5) $1,107,067 aggregate principal amount of mortgages (excluding premiums, discounts and net debt issuance costs) secured by 43 of our properties (45 buildings) with maturity dates between 2017 and 2043. The 43 mortgaged properties (45 buildings) had a carrying value (before accumulated depreciation) of $1,621,656 at March 31, 2017. We also had two properties subject to capital leases with lease obligations totaling $11,278 at March 31, 2017; these two properties had a carrying value (before accumulated depreciation) of $36,125 at March 31, 2017, and the capital leases expire in 2026. In April 2017, we prepaid, at a premium to par of $5,449 plus accrued interest, a mortgage note secured by 17 of our properties with an outstanding principal balance of approximately $277,837, a maturity date in September 2019 and an annual interest rate of 6.71%. In May 2017, we prepaid, at par plus accrued interest, a mortgage note secured by one of our properties with an outstanding principal balance of approximately $10,579, a maturity date in August 2017 and an annual interest rate of 6.15%. In May 2017, we gave notice of our intention to prepay, at par plus accrued interest, a mortgage note secured by one of our properties with an outstanding principal balance of approximately $8,807, a maturity date in August 2037 and an annual interest rate of 5.95%; we expect to make this prepayment in June 2017. We have a $1,000,000 revolving credit facility that is available for general business purposes, including acquisitions. The maturity date of our revolving credit facility is January 15, 2018 and, subject to our payment of an extension fee and meeting other conditions, we have an option to extend the stated maturity date by an additional year to January 15, 2019. Our revolving credit facility provides that we can borrow, repay and re-borrow funds available under our revolving credit facility until maturity, and no principal repayment is due until maturity. Our revolving credit facility requires annual interest to be paid on borrowings at LIBOR plus a premium, which was 130 basis points as of March 31, 2017, plus a facility fee of 30 basis points per annum on the total amount of lending commitments. Both the interest rate premium and the facility fee are subject to adjustment based upon changes to our credit ratings. As of March 31, 2017, the annual interest rate payable on borrowings under our revolving credit facility was 2.2%. The weighted average annual interest rates for borrowings under our revolving credit facility were 2.1% and 1.7% for the three months ended March 31, 2017 and 2016, respectively. As of March 31, 2017, we had $97,000 outstanding and $903,000 available for borrowing, and as of May 4, 2017, we had $384,000 outstanding and $616,000 available for borrowing under our revolving credit facility. We incurred interest expense and other associated costs related to our revolving credit facility of $2,364 and $3,682 for the three months ended March 31, 2017 and 2016, respectively. Our revolving credit facility includes an accordion feature pursuant to which maximum borrowings under the facility may be increased to up to $1,500,000 in certain circumstances. We have a $200,000 term loan, which we borrowed in 2015. This term loan matures in September 2022 and is prepayable without penalty beginning September 29, 2017. This term loan requires annual interest to be paid at LIBOR plus a premium of 180 basis points that is subject to adjustment based upon changes to our credit ratings. At March 31, 2017, the annual interest rate payable for amounts outstanding under this term loan was 2.8%. The weighted average annual interest rate for amounts outstanding under this term loan was 2.6% and 2.3% for the three months ended March 31, 2017 and 2016, respectively. We incurred interest expense and other associated costs related to this term loan of $1,299 and $1,127 for the three months ended March 31, 2017 and 2016, respectively. This term loan includes an accordion feature under which maximum borrowings may be increased to up to $400,000 in certain circumstances. We also have a $350,000 term loan, which we borrowed in 2014. This term loan matures in January 2020 and is prepayable without penalty at any time. This term loan requires annual interest to be paid at LIBOR plus a premium of 140 basis points that is subject to adjustment based upon changes to our credit ratings. At March 31, 2017, the annual interest rate payable on amounts outstanding under this term loan was 2.2%. The weighted average annual interest rate for amounts outstanding under this term loan was 2.2% and 1.9% for the three months ended March 31, 2017 and 2016, respectively. We incurred interest expense and other associated costs related to this term loan of $1,916 and $1,614 for the three months ended March 31, 2017 and 2016, respectively. This term loan includes an accordion feature under which maximum borrowings may be increased to up to $700,000 in certain circumstances. Our revolving credit facility and term loan agreements and our 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 revolving credit facility and term loan agreements, a change of control of us, as defined, which includes The RMR Group LLC, or RMR LLC, ceasing to act as our business and property manager. Our revolving credit facility and term loan agreements and our senior unsecured notes indentures and their supplements also contain a number of covenants, including covenants that restrict our ability to incur debts, and generally require us to maintain certain financial ratios, and our revolving credit facility and term loan agreements 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 revolving credit facility and term loan agreements and our senior unsecured notes indentures and their supplements at March 31, 2017.

Indebtedness

Our principal debt obligations at March 31, 2017 were: (1) outstanding borrowings under our $1,000,000 unsecured revolving credit facility; (2) six public issuances of senior unsecured notes, including: (a) $400,000 principal amount at an annual interest rate of 3.25% due 2019, (b) $200,000 principal amount at an annual interest rate of 6.75% due 2020, (c) $300,000 principal amount at an annual interest rate of 6.75% due 2021, (d) $250,000 principal amount at an annual interest rate of 4.75% due 2024, (e) $350,000 principal amount at an annual interest rate of 5.625% due 2042 and (f) $250,000 principal amount at an annual interest rate of 6.25% due 2046; (3) our $350,000 principal amount term loan due 2020; (4) our $200,000 principal amount term loan due 2022; and (5) $1,107,067 aggregate principal amount of mortgages (excluding premiums, discounts and net debt issuance costs) secured by 43 of our properties (45 buildings) with maturity dates between 2017 and 2043. The 43 mortgaged properties (45 buildings) had a carrying value (before accumulated depreciation) of $1,621,656 at March 31, 2017. We also had two properties subject to capital leases with lease obligations totaling $11,278 at March 31, 2017; these two properties had a carrying value (before accumulated depreciation) of $36,125 at March 31, 2017, and the capital leases expire in 2026.

In April 2017, we prepaid, at a premium to par of $5,449 plus accrued interest, a mortgage note secured by 17 of our properties with an outstanding principal balance of approximately $277,837, a maturity date in September 2019 and an annual interest rate of 6.71%. In May 2017, we prepaid, at par plus accrued interest, a mortgage note secured by one of our properties with an outstanding principal balance of approximately $10,579, a maturity date in August 2017 and an annual interest rate of 6.15%. In May 2017, we gave notice of our intention to prepay, at par plus accrued interest, a mortgage note secured by one of our properties with an outstanding principal balance of approximately $8,807, a maturity date in August 2037 and an annual interest rate of 5.95%; we expect to make this prepayment in June 2017.

We have a $1,000,000 revolving credit facility that is available for general business purposes, including acquisitions. The maturity date of our revolving credit facility is January 15, 2018 and, subject to our payment of an extension fee and meeting other conditions, we have an option to extend the stated maturity date by an additional year to January 15, 2019. Our revolving credit facility provides that we can borrow, repay and re-borrow funds available under our revolving credit facility until maturity, and no principal repayment is due until maturity. Our revolving credit facility requires annual interest to be paid on borrowings at LIBOR plus a premium, which was 130 basis points as of March 31, 2017, plus a facility fee of 30 basis points per annum on the total amount of lending commitments. Both the interest rate premium and the facility fee are subject to adjustment based upon changes to our credit ratings. As of March 31, 2017, the annual interest rate payable on borrowings under our revolving credit facility was 2.2%. The weighted average annual interest rates for borrowings under our revolving credit facility were 2.1% and 1.7% for the three months ended March 31, 2017 and 2016, respectively. As of March 31, 2017, we had $97,000 outstanding and $903,000 available for borrowing, and as of May 4, 2017, we had $384,000 outstanding and $616,000 available for borrowing under our revolving credit facility. We incurred interest expense and other associated costs related to our revolving credit facility of $2,364 and $3,682 for the three months ended March 31, 2017 and 2016, respectively. Our revolving credit facility includes an accordion feature pursuant to which maximum borrowings under the facility may be increased to up to $1,500,000 in certain circumstances.

We have a $200,000 term loan, which we borrowed in 2015. This term loan matures in September 2022 and is prepayable without penalty beginning September 29, 2017. This term loan requires annual interest to be paid at LIBOR plus a premium of 180 basis points that is subject to adjustment based upon changes to our credit ratings. At March 31, 2017, the annual interest rate payable for amounts outstanding under this term loan was 2.8%. The weighted average annual interest rate for amounts outstanding under this term loan was 2.6% and 2.3% for the three months ended March 31, 2017 and 2016, respectively. We incurred interest expense and other associated costs related to this term loan of $1,299 and $1,127 for the three months ended March 31, 2017 and 2016, respectively. This term loan includes an accordion feature under which maximum borrowings may be increased to up to $400,000 in certain circumstances.

We also have a $350,000 term loan, which we borrowed in 2014. This term loan matures in January 2020 and is prepayable without penalty at any time. This term loan requires annual interest to be paid at LIBOR plus a premium of 140 basis points that is subject to adjustment based upon changes to our credit ratings. At March 31, 2017, the annual interest rate payable on amounts outstanding under this term loan was 2.2%. The weighted average annual interest rate for amounts outstanding under this term loan was 2.2% and 1.9% for the three months ended March 31, 2017 and 2016, respectively. We incurred interest expense and other associated costs related to this term loan of $1,916 and $1,614 for the three months ended March 31, 2017 and 2016, respectively. This term loan includes an accordion feature under which maximum borrowings may be increased to up to $700,000 in certain circumstances.

Our revolving credit facility and term loan agreements and our 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 revolving credit facility and term loan agreements, a change of control of us, as defined, which includes The RMR Group LLC, or RMR LLC, ceasing to act as our business and property manager. Our revolving credit facility and term loan agreements and our senior unsecured notes indentures and their supplements also contain a number of covenants, including covenants that restrict our ability to incur debts, and generally require us to maintain certain financial ratios, and our revolving credit facility and term loan agreements 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 revolving credit facility and term loan agreements and our senior unsecured notes indentures and their supplements at March 31, 2017.