Investments in and Advances to Unconsolidated Joint Ventures - Schedule of Equity Method Investments (Details) $ in Thousands	Sep. 30, 2018 USD ($) joint_venture	Dec. 31, 2017 USD ($)	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures	$ 623,255	$ 800,840
CCRC JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	49.00%
Investments in and advances to unconsolidated joint ventures	$ 374,988	400,241
RIDEA II
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	40.00%		40.00%
Investments in and advances to unconsolidated joint ventures	$ 0	259,651
UK JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	49.00%
Investments in and advances to unconsolidated joint ventures	$ 105,200	0
Life Science JVs
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures	$ 67,328	65,581
Life Science JVs | Minimum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	50.00%
Life Science JVs | Maximum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	63.00%
Torrey Pines Science Center, LP
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	50.00%
Britannia Biotech Gateway, LP
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	55.00%
LASDK, LP
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	63.00%
MBK JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	50.00%
Investments in and advances to unconsolidated joint ventures	$ 35,934	38,005
Development JVs
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures	$ 26,100	23,365
Number of unconsolidated joint ventures | joint_venture	4
Development JVs | Minimum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	50.00%
Development JVs | Maximum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	90.00%
Vintage Park Development JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	85.00%
Waldwick
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	85.00%
Otay Ranch
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	90.00%
MBK Development JV
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	50.00%
Medical Office JVs
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures	$ 12,313	12,488
Number of unconsolidated joint ventures | joint_venture	3
Medical Office JVs | Minimum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	20.00%
Medical Office JVs | Maximum
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	67.00%
HCP Ventures IV, LLC
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	20.00%
HCP Ventures III, LLC
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	30.00%
Suburban Properties, LLC
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	67.00%
K&Y JVs
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	80.00%
Investments in and advances to unconsolidated joint ventures	$ 1,380	1,283
Number of unconsolidated joint ventures | joint_venture	3
Advances to unconsolidated joint ventures, net
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures	$ 12	$ 226