Segment Information (Income Statement by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues:
Rental income									$ 1,346,046	$ 1,138,457	$ 1,036,356
Resident fees and services									1,811,255	1,552,951	1,406,005
Medical office building and other services revenue									41,492	29,364	17,809
Income from loans and investments									86,553	51,778	54,425
Interest and other income									1,052	4,263	2,022
Total revenues	$ 841,274	$ 827,606	$ 811,920	$ 805,598	$ 732,090	$ 704,932	$ 674,529	$ 665,262	3,286,398	2,776,813	2,516,617
Less:
Interest and other income									1,052	4,263	2,022
Property-level operating expenses									1,383,640	1,195,388	1,109,925
Medical office building services costs									26,565	17,092	8,315
Segment NOI									1,875,141	1,560,070	1,396,355
Income (loss) from unconsolidated entities									(1,420)	(139)	(508)
Segment profit									1,873,721	1,559,931	1,395,847
Interest and other income									1,052	4,263	2,022
Interest expense									(367,114)	(292,065)	(249,009)
Depreciation and amortization									(894,057)	(725,216)	(629,908)
General, administrative and professional fees									(128,035)	(121,738)	(115,083)
Loss on extinguishment of debt, net									(14,411)	(5,564)	(1,201)
Merger-related expenses and deal costs									(102,944)	(43,304)	(21,634)
Other									(17,957)	(25,743)	(17,364)
Income tax benefit									39,284	8,732	11,828
Discontinued operations	$ (2,331)	$ (22,383)	$ 18,243	$ 17,574	$ 20,709	$ 18,171	$ 30,781	$ 30,074	11,103	99,735	79,171
Gain on real estate dispositions									18,580	17,970	0
Net income									419,222	477,001	454,669
Operating Segments | Triple-net leased properties
Revenues:
Rental income									779,801	674,547	586,016
Resident fees and services									0	0	0
Medical office building and other services revenue									4,433	4,565	4,469
Income from loans and investments									0	0	0
Interest and other income									0	0	0
Total revenues									784,234	679,112	590,485
Less:
Interest and other income									0	0	0
Property-level operating expenses									0	0	0
Medical office building services costs									0	0	0
Segment NOI									784,234	679,112	590,485
Income (loss) from unconsolidated entities									(813)	859	475
Segment profit									783,421	679,971	590,960
Interest and other income									0	0	0
Operating Segments | Senior living operations
Revenues:
Rental income									0	0	0
Resident fees and services									1,811,255	1,552,951	1,406,005
Medical office building and other services revenue									0	0	0
Income from loans and investments									0	0	0
Interest and other income									0	0	0
Total revenues									1,811,255	1,552,951	1,406,005
Less:
Interest and other income									0	0	0
Property-level operating expenses									1,209,415	1,036,556	956,684
Medical office building services costs									0	0	0
Segment NOI									601,840	516,395	449,321
Income (loss) from unconsolidated entities									(526)	(658)	(1,980)
Segment profit									601,314	515,737	447,341
Interest and other income									0	0	0
Operating Segments | MOB operations
Revenues:
Rental income									566,245	463,910	450,340
Resident fees and services									0	0	0
Medical office building and other services revenue									34,436	22,529	12,077
Income from loans and investments									0	0	0
Interest and other income									0	0	0
Total revenues									600,681	486,439	462,417
Less:
Interest and other income									0	0	0
Property-level operating expenses									174,225	158,832	153,241
Medical office building services costs									26,565	17,092	8,315
Segment NOI									399,891	310,515	300,861
Income (loss) from unconsolidated entities									369	398	1,451
Segment profit									400,260	310,913	302,312
Interest and other income									0	0	0
All Other
Revenues:
Rental income									0	0	0
Resident fees and services									0	0	0
Medical office building and other services revenue									2,623	2,270	1,263
Income from loans and investments									86,553	51,778	54,425
Interest and other income									1,052	4,263	2,022
Total revenues									90,228	58,311	57,710
Less:
Interest and other income									1,052	4,263	2,022
Property-level operating expenses									0	0	0
Medical office building services costs									0	0	0
Segment NOI									89,176	54,048	55,688
Income (loss) from unconsolidated entities									(450)	(738)	(454)
Segment profit									88,726	53,310	55,234
Interest and other income									$ 1,052	$ 4,263	$ 2,022