Shareholders' Equity	9 Months Ended
Sep. 30, 2017
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders’ Equity Distributions On January 17, 2017, we paid a $0.4453 per share distribution, or $5,166, to our Series D preferred shareholders. On February 21, 2017, we paid a regular quarterly distribution to common shareholders of record on January 23, 2017 of $0.51 per share, or $83,777. On May 18, 2017, we paid a regular quarterly distribution to common shareholders of record on April 21, 2017 of $0.52 per share, or $85,419. On August 17, 2017, we paid a regular quarterly distribution to common shareholders of record on July 24, 2017 of $0.52 per share, or $85,427. On October 12, 2017, we declared a regular quarterly dividend to common shareholders of record on October 23, 2017 of $0.52 per share, or $85,462. We expect to pay this amount on or about November 16, 2017. Preferred Shares On February 10, 2017, we redeemed all 11,600,000 of our outstanding 7.125% Series D cumulative redeemable preferred shares at the stated liquidation preference of $25.00 per share plus accrued and unpaid distributions to the date of redemption (an aggregate of $291,435). We reduced net income available for common shareholders for the nine months ended September 30, 2017 by $9,893, which represents the amount by which the liquidation preference for our 7.125% Series D cumulative redeemable preferred shares that were redeemed during the period exceeded our carrying amount for those preferred shares as of the date of redemption. Common Share Grants and Purchases On June 15, 2017, we granted 3,000 of our common shares, valued at $30.12 per share, the closing price of our common shares on The Nasdaq Stock Market LLC, or Nasdaq, on that day, to each of our five Trustees as part of their annual compensation. On June 30, 2017, we purchased an aggregate of 499 of our common shares valued at $29.15 per common share, the closing price of our common shares on Nasdaq on that day, from two former employees of The RMR Group LLC, or RMR LLC, in satisfaction of tax withholding and payment obligations in connection with the vesting of awards of our common shares. On September 14, 2017, we granted an aggregate of 85,000 of our common shares to our officers and certain other employees of RMR LLC valued at $28.08 per share, the closing price of our common shares on Nasdaq on that day. On September 19, 2017, we purchased an aggregate of 18,559 of our common shares for $27.98 per common share, the closing price of our common shares on Nasdaq on that day, from certain of our officers and other employees of RMR LLC in satisfaction of tax withholding and payment obligations in connection with the vesting of awards of our common shares. Cumulative Other Comprehensive Income Cumulative other comprehensive income represents the unrealized net gain on our available for sale equity investments and our share of the comprehensive income of Affiliates Insurance Company, or AIC. See Notes 10 and 13 for further information regarding these investments.

Shareholders’ Equity

Distributions

On January 17, 2017, we paid a $0.4453 per share distribution, or $5,166, to our Series D preferred shareholders.

On February 21, 2017, we paid a regular quarterly distribution to common shareholders of record on January 23, 2017 of $0.51 per share, or $83,777. On May 18, 2017, we paid a regular quarterly distribution to common shareholders of record on April 21, 2017 of $0.52 per share, or $85,419. On August 17, 2017, we paid a regular quarterly distribution to common shareholders of record on July 24, 2017 of $0.52 per share, or $85,427. On October 12, 2017, we declared a regular quarterly dividend to common shareholders of record on October 23, 2017 of $0.52 per share, or $85,462. We expect to pay this amount on or about November 16, 2017.

Preferred Shares

On February 10, 2017, we redeemed all 11,600,000 of our outstanding 7.125% Series D cumulative redeemable preferred shares at the stated liquidation preference of $25.00 per share plus accrued and unpaid distributions to the date of redemption (an aggregate of $291,435). We reduced net income available for common shareholders for the nine months ended September 30, 2017 by $9,893, which represents the amount by which the liquidation preference for our 7.125% Series D cumulative redeemable preferred shares that were redeemed during the period exceeded our carrying amount for those preferred shares as of the date of redemption.

Common Share Grants and Purchases

On June 15, 2017, we granted 3,000 of our common shares, valued at $30.12 per share, the closing price of our common shares on The Nasdaq Stock Market LLC, or Nasdaq, on that day, to each of our five Trustees as part of their annual compensation.

On June 30, 2017, we purchased an aggregate of 499 of our common shares valued at $29.15 per common share, the closing price of our common shares on Nasdaq on that day, from two former employees of The RMR Group LLC, or RMR LLC, in satisfaction of tax withholding and payment obligations in connection with the vesting of awards of our common shares.

On September 14, 2017, we granted an aggregate of 85,000 of our common shares to our officers and certain other employees of RMR LLC valued at $28.08 per share, the closing price of our common shares on Nasdaq on that day.

On September 19, 2017, we purchased an aggregate of 18,559 of our common shares for $27.98 per common share, the closing price of our common shares on Nasdaq on that day, from certain of our officers and other employees of RMR LLC in satisfaction of tax withholding and payment obligations in connection with the vesting of awards of our common shares.

Cumulative Other Comprehensive Income

Cumulative other comprehensive income represents the unrealized net gain on our available for sale equity investments and our share of the comprehensive income of Affiliates Insurance Company, or AIC. See Notes 10 and 13 for further information regarding these investments.