DEBT OBLIGATIONS - Consolidated Debt Obligations Outstanding (Details) - Unsecured Debt - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Consolidated debt obligations
Long-term debt, gross	$ 1,851,610,000	$ 1,828,610,000
Plus: premiums/(discounts), net	8,187,000	10,137,000
Net deferred financing costs	(6,211,000)	(8,152,000)
Total Debt Obligations	1,853,586,000	1,830,595,000
$600 million Unsecured Credit Facility
Consolidated debt obligations
Debt instrument, face amount	600,000,000
Long-term debt, gross	$ 23,000,000	0
Seven-Year Term Loan - Swapped to fixed
Consolidated debt obligations
Debt instrument, term	7 years
Long-term debt, gross	$ 250,000,000	250,000,000
Effective interest rate	2.87%
$350.0M 3.95% Guaranteed Notes due 2023
Consolidated debt obligations
Debt instrument, face amount	$ 350,000,000.0
Debt instrument, interest rate, stated percentage	3.95%
Long-term debt, gross	$ 350,000,000	350,000,000
Effective interest rate	3.87%
$350.0M 4.10% Guaranteed Notes due 2024
Consolidated debt obligations
Debt instrument, face amount	$ 350,000,000.0
Debt instrument, interest rate, stated percentage	4.10%
Long-term debt, gross	$ 350,000,000	350,000,000
Effective interest rate	3.78%
$450.0M 3.95% Guaranteed Notes due 2027
Consolidated debt obligations
Debt instrument, face amount	$ 450,000,000.0
Debt instrument, interest rate, stated percentage	3.95%
Long-term debt, gross	$ 450,000,000	450,000,000
Effective interest rate	4.03%
$350.0M 4.55% Guaranteed Notes due 2029
Consolidated debt obligations
Debt instrument, face amount	$ 350,000,000.0
Debt instrument, interest rate, stated percentage	4.55%
Long-term debt, gross	$ 350,000,000	350,000,000
Effective interest rate	4.30%
Indenture IA (Preferred Trust I)
Consolidated debt obligations
Long-term debt, gross	$ 27,062,000	27,062,000
Indenture IB (Preferred Trust I)
Consolidated debt obligations
Long-term debt, gross	25,774,000	25,774,000
Indenture II (Preferred Trust II)
Consolidated debt obligations
Long-term debt, gross	$ 25,774,000	$ 25,774,000
LIBOR \| $600 million Unsecured Credit Facility
Consolidated debt obligations
Variable interest rate	1.10%
LIBOR \| Indenture IA (Preferred Trust I)
Consolidated debt obligations
Variable interest rate	1.25%
LIBOR \| Indenture IB (Preferred Trust I)
Consolidated debt obligations
Variable interest rate	1.25%
LIBOR \| Indenture II (Preferred Trust II)
Consolidated debt obligations
Variable interest rate	1.25%

Consolidated Debt Obligations Abstract.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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