DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Jun. 30, 2018	Dec. 31, 2017
Deposits:
Non-interest-bearing accounts		$ 3,346,777,000	$ 3,265,544,000
Interest-bearing checking		1,012,519,000	971,137,000
Regular savings accounts		1,635,080,000	1,557,500,000
Money market accounts		1,384,684,000	1,422,313,000
Total interest-bearing transaction and saving accounts		4,032,283,000	3,950,950,000
Certificates of deposit less than or equal to $250,000		1,005,192,000	813,997,000
Certificates of deposit greater than $250,000		143,415,000	152,940,000
Total certificates of deposit	[1]	1,148,607,000	966,937,000
Total deposits		8,527,667,000	8,183,431,000
Included in total deposits:
Public fund transaction and savings accounts		200,497,000	198,719,000
Public fund interest-bearing certificates		24,390,000	23,685,000
Total public deposits		224,887,000	222,404,000
Total brokered deposits		280,055,000	57,228,000
CD acquisition premium		$ 0	$ 11,000

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