AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details 5) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Scheduled maturities of available-for sale investment securities, Amortized Cost
Due within one year	$ 435,764,000
Due after one year through five years	1,275,954,000
Due after five years through ten years	311,367,000
Due after ten years	794,762,000
Total available-for-sale investment securities	2,817,847,000
Scheduled maturities of available-for sale investment securities, Estimated Fair Value
Due within one year	434,493,000
Due after one year through five years	1,289,312,000
Due after five years through ten years	311,157,000
Due after ten years	806,123,000
Fair Value	2,841,085,000	2,626,365,000
Par value of securities pledged to secure public deposits	$ 1,880,000,000	$ 1,930,000,000