DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Sep. 30, 2018	Dec. 31, 2017
Deposits:
Non-interest-bearing accounts		$ 3,469,294,000	$ 3,265,544,000
Interest-bearing checking		1,034,678,000	971,137,000
Regular savings accounts		1,627,560,000	1,557,500,000
Money market accounts		1,373,618,000	1,422,313,000
Total interest-bearing transaction and saving accounts		4,035,856,000	3,950,950,000
Certificates of deposit less than or equal to $250,000		1,026,984,000	813,997,000
Certificates of deposit greater than $250,000		153,690,000	152,940,000
Total certificates of deposit	[1]	1,180,674,000	966,937,000
Total deposits		8,685,824,000	8,183,431,000
Included in total deposits:
Public fund transaction and savings accounts		187,759,000	198,719,000
Public fund interest-bearing certificates		25,367,000	23,685,000
Total public deposits		213,126,000	222,404,000
Total brokered deposits		325,154,000	57,228,000
CD acquisition premium		$ 0	$ 11,000

[1] Certificates of deposit include $0 and $11,000 of acquisition premiums at September 30, 2018 and December 31, 2017, respectively.