DERIVATIVE INSTRUMENTS (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Offsetting Assets [Line Items]
Difference in carrying value and fair value, reflecting a gain	$ 3,700,000	$ 2,700,000
Average maturity	60 months	59 months
Average interest receive rate (in hundredths)	2.50%	2.50%
Average interest pay rate (in hundredths)	5.60%	5.80%
Gross Amount Recognized	49,950,000	53,820,000	56,322,000
Gross Amount Offset	0	0	0
Net Amount Recognized	49,950,000	53,820,000	56,322,000
Financial Instruments	0	0	0
Financial Collateral Pledged	0	0	0
Net Amount	49,950,000	53,820,000	56,322,000
Offsetting Liabilities [Line Items]
Gross Amount Recognized	400,994,000	452,297,000	467,387,000
Gross Amount Offset	0	0	0
Net Amount Recognized	400,994,000	452,297,000	467,387,000
Financial Instruments	(353,742,000)	(401,089,000)	(414,611,000)
Financial Collateral Pledged	(46,284,000)	(50,857,000)	(52,154,000)
Net Amount	968,000	351,000	622,000
Forward Commitments [Member]
Offsetting Assets [Line Items]
Notional amount	201,300,000	213,300,000
Difference in carrying value and fair value, reflecting a loss	968,000	98,000
Gross Amount Recognized	3,666,000	2,963,000	4,168,000
Gross Amount Offset	0	0	0
Net Amount Recognized	3,666,000	2,963,000	4,168,000
Financial Instruments	0	0	0
Financial Collateral Pledged	0	0	0
Net Amount	3,666,000	2,963,000	4,168,000
Offsetting Liabilities [Line Items]
Gross Amount Recognized	968,000	351,000	622,000
Gross Amount Offset	0	0	0
Net Amount Recognized	968,000	351,000	622,000
Financial Instruments	0	0	0
Financial Collateral Pledged	0	0	0
Net Amount	968,000	351,000	622,000
Loan/Lease Interest Rate Swaps [Member]
Offsetting Assets [Line Items]
Notional amount	479,100,000	479,400,000
Gross Amount Recognized	46,284,000	50,857,000	52,154,000
Gross Amount Offset	0	0	0
Net Amount Recognized	46,284,000	50,857,000	52,154,000
Financial Instruments	0	0	0
Financial Collateral Pledged	0	0	0
Net Amount	46,284,000	50,857,000	52,154,000
Offsetting Liabilities [Line Items]
Gross Amount Recognized	46,284,000	50,857,000	52,154,000
Gross Amount Offset	0	0	0
Net Amount Recognized	46,284,000	50,857,000	52,154,000
Financial Instruments	0	0	0
Financial Collateral Pledged	(46,284,000)	(50,857,000)	(52,154,000)
Net Amount	0	0	0
Repurchase Arrangements [Member]
Offsetting Liabilities [Line Items]
Gross Amount Recognized	353,742,000	401,089,000	414,611,000
Gross Amount Offset	0	0	0
Net Amount Recognized	353,742,000	401,089,000	414,611,000
Financial Instruments	(353,742,000)	(401,089,000)	(414,611,000)
Financial Collateral Pledged	0	0	0
Net Amount	0	0	0
Fixed Rate Mortgages [Member]
Offsetting Assets [Line Items]
Notional amount	$ 188,400,000	$ 159,100,000