SUBSEQUENT EVENTS (Details) - USD ($)	1 Months Ended
	Apr. 30, 2018	Mar. 31, 2018
Subsequent Event [Line Items]
Par value of common stock (in dollars per share)		$ 1.25
Interest rate		7.50%
Common Stock | Subsequent event
Subsequent Event [Line Items]
Shares available for issuance	12,669,491
Number of shares issued	5,889,830
Par value of common stock (in dollars per share)	$ 1.25
Price per share (in usd per share)	$ 29.50
Consideration received, gross	$ 173,700,000
Consideration received	$ 167,700,000
Common Stock | Over-Allotment Option | Subsequent event
Subsequent Event [Line Items]
Number of shares issued	1,652,542
Capital Units | Subsequent event
Subsequent Event [Line Items]
Number of shares issued	5,750,000
Corporate Unit, stated value per share (in usd per share)	$ 50
Corporate Unit, cash redemption value (in usd per share)	$ 50
Consideration received, gross	287,500,000
Consideration received	$ 278,900,000
Capital Units | Over-Allotment Option | Subsequent event
Subsequent Event [Line Items]
Number of shares issued	750,000
Series 2018A, Due 2031 | Subsequent event
Subsequent Event [Line Items]
Interest rate	3.70%
3.18% Notes, Due April 2021 | Subsequent event
Subsequent Event [Line Items]
Principal amount issued	$ 90,000,000.0
Interest rate	3.18%
Series 2018 B, 3.78% Senior Notes | Subsequent event
Subsequent Event [Line Items]
Principal amount issued	$ 80,000,000.0
Interest rate	3.78%
Term (in years)	10 years
Series 2018 C. 3.88% Senior Notes | Subsequent event
Subsequent Event [Line Items]
Principal amount issued	$ 80,000,000.0
Interest rate	3.88%
Term (in years)	12 years
Scenario, Forecast | Series 2018A, Due 2031 | Capital Units
Subsequent Event [Line Items]
Interest in notes issued, percent	5.00%
Bank of America, N.A. | Common Stock | Private Placement | Subsequent event
Subsequent Event [Line Items]
Number of shares held for forward contract	6,779,661
Unsecured promissory notes | Subsequent event
Subsequent Event [Line Items]
Principal amount issued	$ 250,000,000.0
Line of Credit | Line of Credit | Subsequent event
Subsequent Event [Line Items]
Repayments of debt	116,000,000
Revolving Credit Facility | Line of Credit | Subsequent event
Subsequent Event [Line Items]
Repayments of debt	50,000,000
Bridge Loan | Subsequent event
Subsequent Event [Line Items]
Principal amount issued	$ 1,160,000,000.00