DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Jun. 30, 2019	Dec. 31, 2018
Deposits:
Non-interest-bearing accounts		$ 3,671,995,000	$ 3,657,817,000
Interest-bearing checking		1,187,035,000	1,191,016,000
Regular savings accounts		1,848,048,000	1,842,581,000
Money market accounts		1,511,119,000	1,465,369,000
Total interest-bearing transaction and saving accounts		4,546,202,000	4,498,966,000
Certificates of deposit less than or equal to $250,000		891,312,000	1,143,303,000
Certificates of deposit greater than $250,000		179,458,000	176,962,000
Total certificates of deposit	[1]	1,070,770,000	1,320,265,000
Total deposits		9,288,967,000	9,477,048,000
Included in total deposits:
Public fund transaction and savings accounts		223,610,000	217,401,000
Public fund interest-bearing certificates		28,656,000	30,089,000
Total public deposits		252,266,000	247,490,000
Total brokered deposits		138,395,000	377,347,000
CD acquisition premium		$ 384,000	$ 563,000

[1] Certificates of deposit include $384,000 and $563,000 of acquisition premiums at June 30, 2019 and December 31, 2018, respectively.