Equity Investment in Select Income REIT - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity in earnings of investees	$ 8,581	$ 9,400	$ 11,320	$ 19,334
Investment at carrying value	$ 477,233		477,233		$ 487,708
Cash distributions from SIR			$ 9,345	17,760
SIR
Schedule of Equity Method Investments [Line Items]
Equity investments, common shares owned (in shares)	24,918,421		24,918,421
Percentage of outstanding shares owned	27.90%		27.90%
Equity in earnings of investees	$ 8,207	9,383	$ 10,818	19,240
Equity in unrealized gain (loss) of investees	(389)	2,563	4,103	7,055
The amount of investment in exceed the underlying equity of the investee	88,713		88,713
Accretion in equity of earnings	736	740	1,472	1,480
Investment at carrying value	477,233		477,233
Equity Investments, market value	598,790		598,790
Cash distributions from SIR	$ 12,708	$ 12,459	$ 25,416	$ 24,918