Segment Disclosures - Summary Information for the Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment reporting information, revenues
Rental Revenues	$ 465,106	$ 464,291	$ 922,005	$ 936,347
Resident fees and services	164,202	106,838	329,965	211,851
Operating expenses	(180,125)	(136,342)	(357,080)	(268,373)
NOI	449,183	434,787	894,890	879,825
Non-cash adjustments to NOI	(3,397)	(21,528)	(10,799)	(50,713)
Adjusted (cash) NOI	445,786	413,259	884,091	829,112
Adjusted (cash) NOI from unconsolidated joint ventures	17,570	16,418	34,614	31,962
Interest Income	32,787	35,945	50,816	69,207
Portfolio Income	496,143	465,622	969,521	930,281
Addback non-cash adjustments	3,397	21,528	10,799	50,713
Investment management fee income	81	458	172	918
Interest expense	(121,333)	(118,632)	(243,395)	(235,412)
Depreciation and amortization	(141,386)	(120,403)	(282,708)	(234,925)
General and administrative expenses	(22,793)	(28,845)	(48,292)	(53,618)
Acquisition and pursuit costs	(14,527)	(18,407)	(17,002)	(21,797)
Impairments		(44,835)		(523,299)
Gain (loss) on sales of real estate	119,614	61	119,614	6,325
Other income, net	2,280	11,055	3,502	12,779
Income tax benefit (expense)	2,003	4,563	(51,035)	4,640
Equity (loss) income in unconsolidated joint ventures, excluding adjusted (cash) NOI	(18,637)	(4,417)	(36,589)	(6,360)
Net income (loss)	304,842	167,748	424,587	(69,755)
Corporate Non-segment
Segment reporting information, revenues
Interest expense	(104,715)	(100,724)	(210,125)	(199,910)
General and administrative expenses	(22,793)	(28,845)	(48,292)	(53,618)
Acquisition and pursuit costs	(14,527)	(18,407)	(17,002)	(21,797)
Other income, net	2,280	11,055	3,502	12,779
Income tax benefit (expense)	2,003	4,563	(51,035)	4,640
Net income (loss)	(137,752)	(132,358)	(322,952)	(257,906)
Senior housing | Operating segment
Segment reporting information, revenues
Rental Revenues	131,495	123,910	260,392	251,292
Resident fees and services	164,202	106,838	329,965	211,851
Operating expenses	(117,121)	(76,514)	(233,257)	(152,024)
NOI	178,576	154,234	357,100	311,119
Non-cash adjustments to NOI	(2,502)	1,238	(8,458)	(5,175)
Adjusted (cash) NOI	176,074	155,472	348,642	305,944
Adjusted (cash) NOI from unconsolidated joint ventures	15,310	14,814	30,208	28,826
Interest Income	16,474	12,237	18,359	19,631
Portfolio Income	207,858	182,523	397,209	354,401
Addback non-cash adjustments	2,502	(1,238)	8,458	5,175
Interest expense	(11,885)	(12,198)	(23,904)	(24,288)
Depreciation and amortization	(61,257)	(48,916)	(123,124)	(95,942)
Impairments				61,466
Gain (loss) on sales of real estate	23,940	61	23,940	6,325
Equity (loss) income in unconsolidated joint ventures, excluding adjusted (cash) NOI	(17,790)	(16,774)	(35,180)	(31,452)
Net income (loss)	143,368	103,458	247,399	275,685
Post-acute/skilled nursing | Operating segment
Segment reporting information, revenues
Rental Revenues	110,125	130,895	217,315	271,471
Operating expenses	(589)	(538)	(1,153)	(1,071)
NOI	109,536	130,357	216,162	270,400
Non-cash adjustments to NOI	(173)	(19,077)	(444)	(37,160)
Adjusted (cash) NOI	109,363	111,280	215,718	233,240
Adjusted (cash) NOI from unconsolidated joint ventures	400		804
Interest Income	16,313	23,708	32,457	49,576
Portfolio Income	126,076	134,988	248,979	282,816
Addback non-cash adjustments	173	19,077	444	37,160
Interest expense	(2,475)	(2,492)	(4,805)	(4,768)
Depreciation and amortization	(3,255)	(3,210)	(6,205)	(4,469)
Impairments		(41,887)		(581,817)
Gain (loss) on sales of real estate	57,909		57,909
Equity (loss) income in unconsolidated joint ventures, excluding adjusted (cash) NOI	(182)	13,831	(368)	27,986
Net income (loss)	178,246	120,307	295,954	(243,092)
Life science | Operating segment
Segment reporting information, revenues
Rental Revenues	90,201	85,409	179,149	168,960
Operating expenses	(17,961)	(17,234)	(34,704)	(33,933)
NOI	72,240	68,175	144,445	135,027
Non-cash adjustments to NOI	(545)	(2,745)	(1,218)	(5,820)
Adjusted (cash) NOI	71,695	65,430	143,227	129,207
Adjusted (cash) NOI from unconsolidated joint ventures	1,499	1,298	2,919	2,526
Portfolio Income	73,194	66,728	146,146	131,733
Addback non-cash adjustments	545	2,745	1,218	5,820
Investment management fee income	1	1	2	2
Interest expense	(632)	(764)	(1,270)	(1,528)
Depreciation and amortization	(32,077)	(30,294)	(65,674)	(60,490)
Gain (loss) on sales of real estate	29,455		29,455
Equity (loss) income in unconsolidated joint ventures, excluding adjusted (cash) NOI	(724)	(555)	(1,435)	(1,109)
Net income (loss)	69,762	37,861	108,442	74,428
Medical office | Operating segment
Segment reporting information, revenues
Rental Revenues	111,218	102,585	220,212	200,890
Operating expenses	(43,439)	(40,785)	(85,752)	(79,037)
NOI	67,779	61,800	134,460	121,853
Non-cash adjustments to NOI	(759)	(1,170)	(1,564)	(3,036)
Adjusted (cash) NOI	67,020	60,630	132,896	118,817
Adjusted (cash) NOI from unconsolidated joint ventures	361	306	683	610
Portfolio Income	67,381	60,936	133,579	119,427
Addback non-cash adjustments	759	1,170	1,564	3,036
Investment management fee income	80	457	170	916
Interest expense	(1,626)	(2,454)	(3,291)	(4,918)
Depreciation and amortization	(40,986)	(34,174)	(80,083)	(66,356)
Impairments		(2,948)		(2,948)
Gain (loss) on sales of real estate	8,310		8,310
Equity (loss) income in unconsolidated joint ventures, excluding adjusted (cash) NOI	59	(961)	95	(1,867)
Net income (loss)	33,977	22,026	60,344	47,290
Hospital | Operating segment
Segment reporting information, revenues
Rental Revenues	22,067	21,492	44,937	43,734
Operating expenses	(1,015)	(1,271)	(2,214)	(2,308)
NOI	21,052	20,221	42,723	41,426
Non-cash adjustments to NOI	582	226	885	478
Adjusted (cash) NOI	21,634	20,447	43,608	41,904
Portfolio Income	21,634	20,447	43,608	41,904
Addback non-cash adjustments	(582)	(226)	(885)	(478)
Depreciation and amortization	(3,811)	(3,809)	(7,622)	(7,668)
Equity (loss) income in unconsolidated joint ventures, excluding adjusted (cash) NOI		42	299	82
Net income (loss)	$ 17,241	$ 16,454	$ 35,400	$ 33,840