DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Dec. 31, 2019	Dec. 31, 2018
Deposit Liabilities [Line Items]
Non-interest-bearing checking		$ 3,945,000,000	$ 3,657,817,000
Interest-bearing checking		1,280,003,000	1,191,016,000
Regular savings accounts		1,934,041,000	1,842,581,000
Money market accounts		1,769,194,000	1,465,369,000
Total interest-bearing transaction and savings accounts		4,983,238,000	4,498,966,000
Time Deposits, $250,000 or less		936,940,000	1,143,303,000
Time Deposits, More than $250,000		183,463,000	176,962,000
Interest-bearing certificates	[1]	1,120,403,000	1,320,265,000
Total deposits		10,048,641,000	9,477,048,000
Included in total deposits:
Public fund transaction accounts		244,418,000	217,401,000
Public fund interest-bearing certificates		35,184,000	30,089,000
Total public deposits		279,602,000	247,490,000
Total brokered deposits		202,884,000	377,347,000
Related Party Deposit Liabilities		7,900,000	8,300,000
Business Combination, Acquired Deposits, Time Deposit Premium		269,000	563,000
Time deposits equal to or greater than $250,000		$ 189,000,000.0	$ 180,500,000

[1] )Certificates of deposit included $269,000 of acquisition discounts at December 31, 2019 and $563,000 of acquisition premiums at December 31, 2018.