CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Income from loans and investments									$ 124,218	$ 117,608	$ 98,094
Interest and other income									24,892	6,034	876
Rental income:
Total rental income									1,513,807	1,593,598	1,476,176
Total revenues	$ 923,263	$ 936,538	$ 942,304	$ 943,705	$ 895,288	$ 899,928	$ 895,490	$ 883,443	3,745,810	3,574,149	3,443,522
Expenses
Interest									442,497	448,196	419,740
Depreciation and amortization									919,639	887,948	898,924
Office building services costs									1,418	3,391	7,311
General, administrative and professional fees									151,982	135,490	126,875
Loss on extinguishment of debt, net									58,254	754	2,779
Merger-related expenses and deal costs									30,547	10,535	24,635
Other									66,768	20,052	9,988
Property-level operating expenses:
Property-level operating expenses									1,689,880	1,483,072	1,434,762
Total expenses									3,360,985	2,989,438	2,925,014
Income before unconsolidated entities, real estate dispositions, income taxes, discontinued operations and noncontrolling interests									384,825	584,711	518,508
(Loss) income from unconsolidated entities									(55,034)	(561)	4,358
Gain on real estate dispositions									46,247	717,273	98,203
Income tax benefit									39,953	59,799	31,343
Income from continuing operations	63,302	103,281	169,300	80,108	393,820	615,210	152,991	199,201	415,991	1,361,222	652,412
Discontinued operations	0	0	0	(10)	(15)	(19)	(23)	(53)	(10)	(110)	(922)
Net income	63,302	103,281	169,300	80,098	393,805	615,191	152,968	199,148	415,981	1,361,112	651,490
Net income attributable to noncontrolling interests	1,029	1,309	2,781	1,395	1,251	1,233	1,137	1,021	6,514	4,642	2,259
Net income attributable to common stockholders	$ 62,273	$ 101,972	$ 166,519	$ 78,703	$ 392,554	$ 613,958	$ 151,831	$ 198,127	$ 409,467	$ 1,356,470	$ 649,231
Basic:
Income from continuing operations (USD per share)	$ 0.18	$ 0.29	$ 0.48	$ 0.22	$ 1.11	$ 1.73	$ 0.43	$ 0.56	$ 1.17	$ 3.83	$ 1.89
Net income attributable to common stockholders (USD per share)	0.17	0.29	0.47	0.22	1.10	1.72	0.43	0.56	1.15	3.82	1.88
Diluted:
Income from continuing operations (USD per share)	0.18	0.29	0.47	0.22	1.10	1.71	0.43	0.56	1.16	3.80	1.87
Net income attributable to common stockholders (USD per share)	$ 0.17	$ 0.28	$ 0.46	$ 0.22	$ 1.09	$ 1.71	$ 0.42	$ 0.55	$ 1.14	$ 3.78	$ 1.86
Weighted average shares used in computing earnings per common share:
Basic (in shares)									356,265	355,326	344,703
Diluted (in shares)									359,301	358,566	348,390
Triple Net Leased Properties
Rental income:
Total rental income									$ 737,796	$ 840,131	$ 845,834
Office Operations
Rental income:
Total rental income									776,011	753,467	630,342
Property-level operating expenses:
Property-level operating expenses									243,679	233,007	191,784
Resident Fees and Services
Revenues
Revenue from contracts with customers									2,069,477	1,843,232	1,847,306
Office Building and Other Services Revenue
Revenues
Revenue from contracts with customers									13,416	13,677	21,070
Senior Living Operations
Property-level operating expenses:
Property-level operating expenses									$ 1,446,201	$ 1,250,065	$ 1,242,978