MORTGAGE SERVICING RIGHTS (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Data and assumptions used in fair value calculation [Abstract]
Unpaid principal balance	$ 5,236,852,000	$ 4,413,139,000	$ 5,058,912,000
Weighted-average prepayment speed (CPR) (in hundredths)	15.40%	18.10%	17.10%
Discount rate (annual percentage) (in hundredths)	10.80%	10.30%	10.80%
Weighted-average coupon interest rate (percentage) (in hundredths)	4.30%	4.80%	4.40%
Weighted-average remaining maturity (months)	306 months	310 months	307 months
Weighted-average servicing fee basis points (in hundredths)	26.90%	27.80%	27.10%
Contractually specified servicing fees, late fees, and ancillary fees [Abstract]
Contractual servicing fees	3,500,000	3,100,000
Late and other ancillary fees	360,000,000	362,000,000
Closed End Loans for One-to-Four Family Residences, Secured by First Liens [Member]
Activity in mortgage servicing asset [Roll Forward]
Fair value as of beginning of period	37,882,000	30,174,000	30,174,000
Additions [Abstract]
Origination of servicing assets	4,268,000	3,525,000
Changes in fair value [Abstract]
Due to payoffs/paydowns	(1,705,000)	(1,726,000)
Due to change in valuation inputs or assumptions used in the valuation model	1,037,000	3,697,000
Other changes in fair value	(4,000)	(2,000)
Fair value as of end of period	$ 41,478,000	$ 35,668,000