Fair Value of Assets and Liabilities - Assets and Liabilities (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 26, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liability	$ 197,788		$ 197,788			$ 219,653
Unrealized gain (loss) on equity securities	$ (64,448)	$ 23,265	$ (41,516)	$ 50,506
Five Star
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities investment (in shares)	4,235,000		4,235,000
Recurring | RMR Inc
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	$ 123,905		$ 123,905
Share price (in dollars per share)					$ 40.00
Recurring | Five Star
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	1,953		1,953
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | RMR Inc
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	123,905		123,905
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Five Star
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	1,953		1,953
Recurring | Significant Other Observable Inputs (Level 2) | RMR Inc
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	0		0
Recurring | Significant Other Observable Inputs (Level 2) | Five Star
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	0		0
Recurring | Significant Unobservable Inputs (Level 3) | RMR Inc
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	0		0
Recurring | Significant Unobservable Inputs (Level 3) | Five Star
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in affiliates, fair value	0		0
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate properties held for sale	7,613		7,613
Other Liability	18,409		18,409
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate properties held for sale	0		0
Other Liability	0		0
Nonrecurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate properties held for sale	7,613		7,613
Other Liability	18,409		18,409
Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate properties held for sale	0		0
Other Liability	$ 0		$ 0
Class A common shares | RMR Inc
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities investment (in shares)	2,637,408		2,637,408
Historical cost basis for shares owned	$ 69,826		$ 69,826
Unrealized gain (loss) on equity securities	$ (36,925)		$ (16,089)
Common Shares | Five Star
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities investment (in shares)	4,235,000		4,235,000
Historical cost basis for shares owned	$ 6,353		$ 6,353
Unrealized gain (loss) on equity securities	(2,176)		(80)
Disposal Group, Held-for-sale, Not Discontinued Operations | Class A common shares | RMR Inc
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on equity securities	(18,409)		(18,409)
Expense related to sale of investment	$ 6,938		$ 6,938