Other Assets (Details) $ in Thousands	1 Months Ended						6 Months Ended	12 Months Ended
	Jun. 30, 2016 GBP (£)	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2012 GBP (£)	Jun. 30, 2012 USD ($)	Jun. 30, 2016 GBP (£)	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 GBP (£)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 GBP (£)	Jun. 30, 2015 USD ($)
Other assets
Straight-line rent receivables, net of allowance of $33,121 and $33,648, respectively										$ 379,002	$ 370,296
Allowance on straight-line rent receivables										31,121	33,648
Marketable debt securities, net										84,128	102,958
Leasing costs and inducements, net										156,303	158,708
Goodwill										50,346	50,346
Other										121,652	119,965
Total other assets										791,431	802,273
Loans receivables										708,096	768,743
Four Seasons Health Care
Other assets
Other-than-temporary impairment on securities			$ 70,000	$ 42,000
Debt Instrument, Face Amount | £					£ 175,000,000
Four Seasons
Other assets
Marketable debt securities, net	£ 50,000,000						£ 50,000,000	£ 58,000,000		$ 66,000	$ 85,000	£ 66,000,000	$ 100,000	£ 111,000,000	$ 174,000
Marketable debt security, par value | £					138,500,000
Purchase of debt securities					£ 136,800,000	$ 215,000
Portion of debt held, as a percent.					79.00%	79.00%
Interest payment received	£ 8,000,000	$ 13,000						£ 8,000,000	$ 13,000
Annual interest rate (as a percent)							12.25%