Investments in and Advances to Unconsolidated Joint Ventures - Schedule of Equity Method Investments (Details) $ in Thousands, £ in Millions	1 Months Ended			3 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 GBP (£)	Dec. 31, 2019 USD ($)	Dec. 31, 2019	Dec. 31, 2019 property	Dec. 31, 2019 joint_venture	Dec. 31, 2019 USD ($)	Oct. 31, 2019	Dec. 31, 2018 USD ($) joint_venture
Schedule of Equity Method Investments [Line Items]
Advances to unconsolidated joint ventures, net								$ 76		$ 71
Investments in and advances to unconsolidated joint ventures								825,515		540,088
SHOP JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		54.00%	54.00%	54.00%	54.00%
Equity method investments								428,258		0
Number of unconsolidated joint ventures (in joint ventures) | property						19
CCRC JV Investment
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		49.00%	49.00%	49.00%	49.00%				49.00%
Equity method investments								325,830		365,764
Number of unconsolidated joint ventures (in joint ventures) | property						15
U.K. JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		49.00%	49.00%	49.00%	49.00%
Equity method investments								0		101,735
Number of unconsolidated joint ventures (in joint ventures) | property						0
Proceeds from sale of equity method investments		$ 91,000	£ 70
MBK JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		50.00%	50.00%	50.00%	50.00%
Equity method investments								33,415		35,435
Number of unconsolidated joint ventures (in joint ventures) | property						4
Unconsolidated development joint ventures
Schedule of Equity Method Investments [Line Items]
Equity method investments								26,876		25,493
Number of unconsolidated joint ventures (in joint ventures) | property						5
Unconsolidated development joint ventures | Minimum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		41.00%	41.00%	41.00%	41.00%
Unconsolidated development joint ventures | Maximum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		90.00%	90.00%	90.00%	90.00%
Waldwick
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		85.00%	85.00%	85.00%	85.00%
Otay Ranch
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		90.00%	90.00%	90.00%	90.00%
MBK Development JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		50.00%	50.00%	50.00%	50.00%
Discovery Naples JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		41.00%	41.00%	41.00%	41.00%
Preferred equity method investment, return percentage					10.00%
Discovery Sarasota JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		47.00%	47.00%	47.00%	47.00%
Medical Office JVs
Schedule of Equity Method Investments [Line Items]
Equity method investments								9,845		10,160
Number of unconsolidated joint ventures (in joint ventures)						3	3
Medical Office JVs | Minimum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		20.00%	20.00%	20.00%	20.00%
Medical Office JVs | Maximum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		67.00%	67.00%	67.00%	67.00%
HCP Ventures IV, LLC
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		20.00%	20.00%	20.00%	20.00%
H C P Ventures III, LLC
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		30.00%	30.00%	30.00%	30.00%
Suburban Properties, LLC
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		67.00%	67.00%	67.00%	67.00%
K&Y JVs
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage		80.00%	80.00%	80.00%	80.00%
Equity method investments								$ 1,215		$ 1,430
Number of unconsolidated joint ventures (in joint ventures)						2	1			3
Proceeds from sale of equity method investments				$ 4,000
Subsequent Event | K&Y JVs
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of equity method investments	$ 12,000