DEPOSITS (Deposit Liabilities) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Deposit Liabilities [Line Items]
Non-interest-bearing checking	$ 1,298,866,000	$ 1,115,346,000
Interest-bearing checking	439,480,000	422,910,000
Regular savings accounts	901,142,000	798,764,000
Money market accounts	488,946,000	408,211,000
Total transaction and savings accounts	3,128,434,000	2,745,231,000
Non-interest-bearing accounts, percent of total	33.30%	30.80%
Interest-bearing checking, percent of total	11.30%	11.70%
Regular savings accounts, percent of total	23.10%	22.10%
Money market accounts, percent of total	12.50%	11.30%
Total transaction and saving accounts, percent of total	80.20%	75.90%
Certificates of deposit:
Total certificates of deposit	770,516,000	872,695,000
Total certificate accounts, percent of total	19.80%	24.10%
Total deposits	3,898,950,000	3,617,926,000	3,557,804,000	3,475,654,000
Total deposits, percent of total	100.00%	100.00%
Included in total deposits:
Public fund transaction accounts	102,854,000	87,521,000
Public fund interest-bearing certificates	35,346,000	51,465,000
Total public deposits	138,200,000	138,986,000
Public fund transaction accounts, percent of total	2.60%	2.40%
Public fund interest-bearing certificates, percent of total	0.90%	1.40%
Total public deposits, percent of total	3.50%	3.80%
Total brokered deposits	4,799,000	4,291,000
Total brokered deposits, percent of total	0.10%	0.10%
Related Party Deposit Liabilities	6,200,000	6,700,000
Up to 1.00% [Member]
Certificates of deposit:
Total certificates of deposit	643,065,000	723,891,000
Total certificate accounts, percent of total	16.50%	20.00%
Included in total deposits:
Certificates of deposit, interest rate, upper range limit	1.00%
1.01% to 2.00% [Member]
Certificates of deposit:
Total certificates of deposit	87,661,000	95,663,000
Total certificate accounts, percent of total	2.30%	2.60%
Included in total deposits:
Certificates of deposit, interest rate, lower range limit	1.01%
Certificates of deposit, interest rate, upper range limit	2.00%
2.01% to 3.00% [Member]
Certificates of deposit:
Total certificates of deposit	32,184,000	43,062,000
Total certificate accounts, percent of total	0.80%	1.20%
Included in total deposits:
Certificates of deposit, interest rate, lower range limit	2.01%
Certificates of deposit, interest rate, upper range limit	3.00%
3.01% to 4.00% [Member]
Certificates of deposit:
Total certificates of deposit	3,024,000	6,663,000
Total certificate accounts, percent of total	0.10%	0.20%
Included in total deposits:
Certificates of deposit, interest rate, lower range limit	3.01%
Certificates of deposit, interest rate, upper range limit	4.00%
4.01% and greater [Member]
Certificates of deposit:
Total certificates of deposit	$ 4,582,000	$ 3,416,000
Total certificate accounts, percent of total	0.10%	0.10%
Included in total deposits:
Certificates of deposit, interest rate, lower range limit	4.01%