DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Sep. 30, 2017	Dec. 31, 2016
Deposits:
Non-interest-bearing accounts		$ 3,379,841,000	$ 3,140,451,000
Interest-bearing checking		955,486,000	914,484,000
Regular savings accounts		1,577,292,000	1,523,391,000
Money market accounts		1,525,657,000	1,497,755,000
Total interest-bearing transaction and saving accounts		4,058,435,000	3,935,630,000
Certificates of deposit less than or equal to $250,000		945,161,000	884,403,000
Certificates of deposit greater than $250,000		155,413,000	160,930,000
Total certificates of deposit	[1]	1,100,574,000	1,045,333,000
Total deposits		8,538,850,000	8,121,414,000
Included in total deposits:
Public fund transaction and savings accounts		194,519,000	221,765,000
Public fund interest-bearing certificates		26,543,000	25,650,000
Total public deposits		221,062,000	247,415,000
Total brokered deposits		171,718,000	34,074,000
CD acquisition premium		$ 30,000	$ 426,000

[1] Certificates of deposit include $30,000 and $426,000 of acquisition premiums at September 30, 2017 and December 31, 2016, respectively.