SECURITIES PURCHASED UNDER RESALE AGREEMENTS (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
SECURITIES PURCHASED UNDER RESALE AGREEMENTS
Securities purchased under resale agreements	$ 1,450,000	$ 786,434
Additions of resale agreements	1,400,000	1,292,066	950,000
Paydowns and maturities of resale agreements	736,434	1,005,632	680,000
Total interest income on resale agreements	$ 20,392	$ 19,216	$ 14,208