SECURITIES PURCHASED UNDER RESALE AGREEMENTS (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
SECURITIES PURCHASED UNDER RESALE AGREEMENTS
Securities purchased under resale agreements	$ 786,434	$ 500,000
Additions of resale agreements	1,292,066	950,000	30,044
Paydowns and maturities of resale agreements	1,005,632	680,000
Total interest income on resale agreements	$ 19,216	$ 14,208	$ 7,985