Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012
Segment reporting
Number of operating segments									4
Number of reportable segments									3
Revenues:
Rental income									$ 526,703	$ 459,380	$ 450,769
Residents fees and services									318,184	302,058	184,031
Total revenues	229,809	216,873	206,708	191,497	200,336	187,265	186,928	186,909	844,887	761,438	634,800
Expenses:
Property operating expenses									324,564	299,878	197,696
Depreciation									185,391	153,026	139,042
General and administrative									38,946	32,657	31,517
Acquisition related costs									4,607	3,378	9,394
Impairment of assets							32,267		(10)	7,989	3,071
Total expenses									553,498	496,928	380,720
Operating income									291,389	264,510	254,080
Interest and other income									425	711	1,117
Interest expense									(135,114)	(117,819)	(117,240)
Loss on early extinguishment of debt									(12)	(797)	(6,349)
Gain on lease terminations											375
Income (loss) before income tax expense and equity in earnings of an investee									156,688	146,605	131,983
Income tax expense									(576)	(600)	(375)
Equity in earnings of an investee									87	334	316
Income from continuing operations									156,199	146,339	131,924
Discontinued Operations:
Income from discontinued operations									1,362	5,043	4,061
Impairment of assets from discontinued operations									(4,377)	(37,610)
Income before gain on sale of properties									153,184	113,772	135,985
Gain on sale of properties									5,453	37,392	(101)
Net income	45,288	37,112	37,659	38,580	72,206	38,125	5,598	35,235	158,637	151,164	135,884
Total assets	5,968,269				4,764,666				5,968,269	4,764,666	4,748,002
Triple Net Leased Net Senior Living Communities
Revenues:
Rental income									230,718	237,209	246,948
Total revenues									230,718	237,209	246,948
Expenses:
Depreciation									61,825	66,854	68,419
Impairment of assets									(10)	6,685
Total expenses									61,815	73,539	68,419
Operating income									168,903	163,670	178,529
Interest expense									(25,473)	(26,501)	(35,530)
Loss on early extinguishment of debt									128
Gain on lease terminations											375
Income (loss) before income tax expense and equity in earnings of an investee									143,558	137,169	143,374
Income from continuing operations									143,558	137,169	143,374
Discontinued Operations:
Income before gain on sale of properties									143,558	137,169	143,374
Gain on sale of properties									5,453	37,392
Net income									149,011	174,561	143,374
Total assets	1,777,684				1,778,591				1,777,684	1,778,591	1,817,253
Managed Senior Living Communities
Revenues:
Residents fees and services									318,184	302,058	184,031
Total revenues									318,184	302,058	184,031
Expenses:
Property operating expenses									245,093	233,711	138,819
Depreciation									32,462	28,972	19,437
Total expenses									277,555	262,683	158,256
Operating income									40,629	39,375	25,775
Interest expense									(10,599)	(12,217)	(11,769)
Loss on early extinguishment of debt									(140)
Income (loss) before income tax expense and equity in earnings of an investee									29,890	27,158	14,006
Income from continuing operations									29,890	27,158	14,006
Discontinued Operations:
Income before gain on sale of properties									29,890	27,158	14,006
Net income									29,890	27,158	14,006
Total assets	961,618				979,152				961,618	979,152	949,974
MOBs
Revenues:
Rental income									278,041	204,594	186,065
Total revenues									278,041	204,594	186,065
Expenses:
Property operating expenses									79,471	66,167	58,877
Depreciation									87,312	53,408	47,394
Impairment of assets											3,071
Total expenses									166,783	119,575	109,342
Operating income									111,258	85,019	76,723
Interest expense									(5,844)	(5,466)	(3,255)
Income (loss) before income tax expense and equity in earnings of an investee									105,414	79,553	73,468
Income from continuing operations									105,414	79,553	73,468
Discontinued Operations:
Income from discontinued operations									1,362	5,043	4,061
Impairment of assets from discontinued operations									(4,377)	(37,610)
Income before gain on sale of properties									102,399	46,986	77,529
Gain on sale of properties											(101)
Net income									102,399	46,986	77,428
Total assets	2,922,623				1,727,497				2,922,623	1,727,497	1,684,434
All Other Operations
Revenues:
Rental income									17,944	17,577	17,756
Total revenues									17,944	17,577	17,756
Expenses:
Depreciation									3,792	3,792	3,792
General and administrative									38,946	32,657	31,517
Acquisition related costs									4,607	3,378	9,394
Impairment of assets										1,304
Total expenses									47,345	41,131	44,703
Operating income									(29,401)	(23,554)	(26,947)
Interest and other income									425	711	1,117
Interest expense									(93,198)	(73,635)	(66,686)
Loss on early extinguishment of debt										(797)	(6,349)
Income (loss) before income tax expense and equity in earnings of an investee									(122,174)	(97,275)	(98,865)
Income tax expense									(576)	(600)	(375)
Equity in earnings of an investee									87	334	316
Income from continuing operations									(122,663)	(97,541)	(98,924)
Discontinued Operations:
Income before gain on sale of properties									(122,663)	(97,541)	(98,924)
Net income									(122,663)	(97,541)	(98,924)
Total assets	$ 306,344				$ 279,426				$ 306,344	$ 279,426	$ 296,341