MORTGAGE SERVICING RIGHTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Data and assumptions used in fair value calculation [Abstract]
Unpaid principal balance	$ 5,942,736	$ 5,649,897	$ 5,942,736	$ 5,649,897	$ 5,686,756
Weighted-average prepayment speed (CPR)	11.10%	10.60%			11.60%
Discount rate (annual percentage) (in hundredths)	9.80%	9.80%			9.80%
Weighted-average coupon interest rate (percentage) (in hundredths)	4.10%	4.10%			4.10%
Weighted-average remaining maturity (months)	317 months	313 months			314 months
Weighted-average servicing fee (basis points)	0.266%	0.265%			0.265%
Activity in mortgage servicing asset [Roll Forward]
Fair value as of beginning of period			51,296	54,662	$ 54,662
Origination of servicing assets			11,074	6,425
Due to payoffs/paydowns			(5,366)	(4,313)
Due to change in valuation inputs or assumptions used in the valuation model			(4,026)	(3,010)
Other changes in fair value			(5)	(5)
Fair value as of end of period	$ 52,973	$ 53,759	52,973	53,759	$ 51,296
Contractually specified servicing fees, late fees, and ancillary fees [Abstract]
Contractual servicing fees	4,000	3,800	11,900	11,300
Late and other ancillary fees	$ 320	$ 293	$ 982	$ 933