Dispositions and Real Property Held for Sale (Summary of Real Property Disposition Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Real property dispositions:
Total dispositions	$ 1,900,930	$ 1,125,117	$ 1,011,218
Gain (loss) on sales of real property, net	748,041	415,575	344,250
Net other assets (liabilities) disposed	1,679	1,178	22,546
Proceeds from real property sales	2,650,650	1,541,870	1,378,014
Seniors Housing Operating
Real property dispositions:
Total dispositions	1,232,816	36,627	74,832
Triple-net
Real property dispositions:
Total dispositions	667,632	835,093	916,689
Outpatient Medical
Real property dispositions:
Total dispositions	$ 482	$ 253,397	$ 19,697