Dispositions and Real Property Held for Sale (Summary of Real Property Disposition Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Real estate dispositions:
Total dispositions	$ 3,097,299	$ 1,900,930	$ 1,125,117
Gain (loss) on real estate dispositions, net	1,088,455	748,041	415,575
Net other assets (liabilities) disposed	114,274	1,679	1,178
Proceeds from real estate dispositions	4,300,028	2,650,650	1,541,870
Seniors Housing Operating
Real estate dispositions:
Total dispositions	1,289,769	1,232,816	36,627
Triple-net
Real estate dispositions:
Total dispositions	51,666	667,632	835,093
Outpatient Medical
Real estate dispositions:
Total dispositions	$ 1,755,864	$ 482	$ 253,397