DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016
Deposit Liabilities [Line Items]
Non-interest-bearing checking		$ 3,265,544,000	$ 3,140,451,000
Interest-bearing checking		971,137,000	914,484,000
Regular savings accounts		1,557,500,000	1,523,391,000
Money market accounts		1,422,313,000	1,497,755,000
Total interest-bearing transaction and savings accounts		3,950,950,000	3,935,630,000
Time Deposits, $250,000 or less		813,997,000	884,403,000
Time Deposits, More than $250,000		152,940,000	160,930,000
Interest-bearing certificates	[1]	966,937,000	1,045,333,000
Total deposits		8,183,431,000	8,121,414,000
Included in total deposits:
Public fund transaction accounts		198,719,000	221,765,000
Public fund interest-bearing certificates		23,685,000	25,650,000
Total public deposits		222,404,000	247,415,000
Total brokered deposits		57,228,000	34,074,000
Related Party Deposit Liabilities		10,000,000	7,200,000
Business Combination, Acquired Deposits, Time Deposit Premium		11,000	426,000
Time deposits equal to or greater than $250,000		$ 155,900,000	$ 165,400,000

[1] )Certificates of deposit included $11,000 and $426,000 of acquisition premiums at December 31, 2017 and 2016, respectively.