FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Assets:
Investments in direct financing leases - net	$ 132,262	$ 364,965
Mortgage notes receivable - net	710,858	671,232
Other investments - net	504,626	276,342
Total	1,347,746	1,312,539
Liabilities:
Revolving line of credit	313,000	290,000
U.S. term loan	423,065	422,498
Sterling term loan	127,394	134,360
Omega OP term loan	99,553	99,423
2015 term loan	248,713	248,390
HUD debt - net		53,098
Subordinated debt - net	20,270	20,376
Other		1,500
Total	4,540,622	4,572,158
Carrying (Reported) Amount, Fair Value Disclosure [Member] | 4.375% notes due 2023
Liabilities:
Notes Payable	694,643	693,474
Carrying (Reported) Amount, Fair Value Disclosure [Member] | 4.95% notes due 2024
Liabilities:
Notes Payable	394,691	393,680
Carrying (Reported) Amount, Fair Value Disclosure [Member] | 4.50% notes due 2025
Liabilities:
Notes Payable	395,402	394,640
Carrying (Reported) Amount, Fair Value Disclosure [Member] | 5.25% notes due 2026
Liabilities:
Notes Payable	595,027	594,321
Carrying (Reported) Amount, Fair Value Disclosure [Member] | 4.50% notes due 2027
Liabilities:
Notes Payable	687,981	686,516
Carrying (Reported) Amount, Fair Value Disclosure [Member] | 4.75% notes due 2028
Liabilities:
Notes Payable	540,883	539,882
Estimate Of Fair Value, Fair Value Disclosure [Member]
Assets:
Investments in direct financing leases - net	132,262	364,965
Mortgage notes receivable - net	735,892	686,772
Other investments - net	503,907	281,031
Total	1,372,061	1,332,768
Liabilities:
Revolving line of credit	313,000	290,000
U.S. term loan	425,000	425,000
Sterling term loan	127,990	135,130
Omega OP term loan	100,000	100,000
2015 term loan	250,000	250,000
HUD debt - net		51,817
Subordinated debt - net	22,589	23,646
Other		1,500
Total	4,551,912	4,665,603
Estimate Of Fair Value, Fair Value Disclosure [Member] | 4.375% notes due 2023
Liabilities:
Notes Payable	700,062	711,190
Estimate Of Fair Value, Fair Value Disclosure [Member] | 4.95% notes due 2024
Liabilities:
Notes Payable	406,386	420,604
Estimate Of Fair Value, Fair Value Disclosure [Member] | 4.50% notes due 2025
Liabilities:
Notes Payable	392,122	399,874
Estimate Of Fair Value, Fair Value Disclosure [Member] | 5.25% notes due 2026
Liabilities:
Notes Payable	605,700	625,168
Estimate Of Fair Value, Fair Value Disclosure [Member] | 4.50% notes due 2027
Liabilities:
Notes Payable	671,555	681,007
Estimate Of Fair Value, Fair Value Disclosure [Member] | 4.75% notes due 2028
Liabilities:
Notes Payable	$ 537,508	$ 550,667