DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Sep. 30, 2020	Dec. 31, 2019
Deposits:
Non-interest-bearing accounts		$ 5,412,570,000	$ 3,945,000,000
Interest-bearing checking		1,434,224,000	1,280,003,000
Regular savings accounts		2,332,287,000	1,934,041,000
Money market accounts		2,120,908,000	1,769,194,000
Total interest-bearing transaction and saving accounts		5,887,419,000	4,983,238,000
Certificates of deposit less than or equal to $250,000		723,225,000	936,940,000
Certificates of deposit greater than $250,000		192,127,000	183,463,000
Total certificates of deposit	[1]	915,352,000	1,120,403,000
Total deposits		12,215,341,000	10,048,641,000
Included in total deposits:
Public fund transaction and savings accounts		259,929,000	244,418,000
Public fund interest-bearing certificates		54,219,000	35,184,000
Total public deposits		314,148,000	279,602,000
Total brokered deposits		0	202,884,000
CD acquisition premium		$ 101,000	$ 269,000

[1] Certificates of deposit include $101,000 and $269,000 of acquisition premiums at September 30, 2020 and December 31, 2019, respectively.