COMMON STOCK - Public Offerings (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended
	Jan. 15, 2019	Apr. 30, 2018	Mar. 31, 2019
Class of Stock [Line Items]
Par value of common stock (in dollars per share)			$ 1.25
Number of shares issued			6,779,661
Interest rate			7.50%
Quarterly contract adjustment payments, percent		3.55%
Common Stock
Class of Stock [Line Items]
Shares available for issuance (in shares)		12,669,491
Par value of common stock (in dollars per share)		$ 1.25
Price per share (in dollars per share)		$ 29.50
Number of shares issued		5,889,830
Consideration received	$ 189.0
Capital Units
Class of Stock [Line Items]
Number of shares issued		5,750,000
Corporate Unit, stated value per share (in dollars per share)		$ 50
Over-Allotment Option | Capital Units
Class of Stock [Line Items]
Number of shares issued		750,000
Bank of America, N.A. | Private Placement | Common Stock
Class of Stock [Line Items]
Number of shares held for forward contract	6,779,661
Series 2018A, Due 2031
Class of Stock [Line Items]
Interest rate		3.70%
Series 2018A, Due 2031 | Capital Units
Class of Stock [Line Items]
Interest in notes issued, percent		5.00%