FEDERAL HOME LOAN BANK (FHLB) ADVANCES (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
FHLB advances
Total FHLB advances	$ 711,500	$ 707,500
Weighted average interest rate (as percent)	1.66%
Additional collateralized advances available	$ 559,000	452,000
Overnight advance with an interest rate of 0.15% due on April 1, 2015
FHLB advances
Total FHLB advances	182,000	198,000
Variable interest rate advance indexed to 3-Month Libor plus 0.14% due on December 19, 2015
FHLB advances
Total FHLB advances	$ 10,000	$ 10,000
Variable interest rate advance indexed to 3-Month Libor plus 0.14% due on December 19, 2015 | London Interbank Offered Rate (LIBOR) [Member]
FHLB advances
Variable interest rate basis	3-Month LIBOR	3-Month LIBOR
Applicable margin (as a percent)	0.14%	0.14%
Fixed interest rate advances with a weighted average interest rate of 1.68% due through 2023
FHLB advances
Total FHLB advances	$ 419,500	$ 399,500
Weighted average interest rate (as percent)	1.68%	1.68%
Putable fixed interest rate advances with a weighted average interest rate of 4.39% due through 2017
FHLB advances
Total FHLB advances	$ 100,000	$ 100,000
Weighted average interest rate (as percent)	4.39%	4.39%
Putable fixed interest rate advances with a weighted average interest rate of 4.39% due through 2017 | Minimum
FHLB advances
Original fixed rate periods	1 year
Original maturities	3 years
Putable fixed interest rate advances with a weighted average interest rate of 4.39% due through 2017 | Maximum
FHLB advances
Original fixed rate periods	5 years
Original maturities	10 years
Various other unsecured lines of credit
FHLB advances
Unsecured lines of credit	$ 166,000	$ 166,000
Federal Home Loan Bank overnight advances
FHLB advances
Total FHLB advances	$ 182,000	$ 198,000
Weighted average interest rate (as percent)	0.19%	0.14%