INVESTMENTS - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Trading securities	$ 0
Weighted average duration of MBS portfolio	5 years
Securities pledged as collateral	$ 1,400,000,000		$ 1,300,000,000
Sale of investment securities available for sale, including interest	9,300,000	$ 30,600,000
Debt securities, available-for-sale, realized gain	300,000	700,000
Losses from sale of available-for-sale securities	0	0
Unamortized premiums	66,100,000		60,400,000
Unaccreted discounts	3,400,000		2,600,000
Owned investment securities	1,800,000,000
Total unrealized losses on securities	63,700,000
Held-to-maturity debt securities with an amortized cost basis	103,500,000		111,700,000
Allowance for Credit Losses	0		0
Accrued interest	900,000		1,100,000
Equity investments	10,200,000		$ 9,500,000
Common Stock | Common Class B
Debt Securities, Available-for-sale [Line Items]
Unrealized gains on equity investments, net	$ 0	3,000,000.0
Other investments
Debt Securities, Available-for-sale [Line Items]
Impairment loss		$ 2,300,000