Other Assets (Details) $ in Thousands	1 Months Ended				3 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2012 GBP (£)	Jun. 30, 2012 USD ($)	Mar. 31, 2016 USD ($) item	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Other assets
Straight-line rent receivables, net of allowance of $33,012 and $33,648, respectively					$ 377,464			$ 370,296
Allowance on straight-line rent receivables					33,012			33,648
Marketable debt securities, net					100,915			102,958
Leasing costs and inducements, net					157,443			158,708
Goodwill					50,346			50,346
Other					131,111			119,965
Total other assets					817,279			802,273
Loans receivables					768,896			768,743
Four Seasons Health Care Ltd
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					$ 83,000	£ 58,000,000		85,000
Marketable debt security, par value			138,500,000			28,000,000		42,000
Marketable debt security, issued and outstanding | £						40,000,000
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
Annual interest rate (as a percent)					12.25%
Brookdale JV
Other assets
Loans receivables					$ 5,000			$ 9,000
Number of installments | item					8