FAIR VALUE (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Available-for-sale investment securities:
Total available-for-sale investment securities	$ 2,622,779,000us-gaap_AvailableForSaleSecurities	$ 2,472,925,000us-gaap_AvailableForSaleSecurities
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Discount on appraisal value of foreclosed real estate, minimum (in hundredths)	10.00%
Discount on appraisal value of foreclosed real estate, maximum (in hundredths)	49.00%
Mortgage servicing rights valuation allowance	0
Fair value of MSRs at end of period	1,400,000
Carrying value before valuation allowance at end of period	1,100,000us-gaap_ServicingAssetAtAmortizedValue
Recurring [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	1,676,112,000	1,517,733,000
Obligations of state and political subdivisions	672,709,000	671,903,000
Government agency mortgage-backed securities	229,526,000	237,728,000
Corporate debt securities	27,026,000	27,091,000
Government agency collateralized mortgage obligations	16,980,000	18,025,000
Marketable equity securities	426,000	445,000
Total available-for-sale investment securities	2,622,779,000	2,472,925,000
Mortgages loans held for sale	1,437,000	1,042,000
Commitments to originate real estate loans for sale	152,000	185,000
Forward sales commitments	(22,000)	(43,000)
Total	2,624,346,000	2,474,109,000
Recurring [Member] \| Level 1 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	1,676,112,000	1,496,667,000
Obligations of state and political subdivisions	0	0
Government agency mortgage-backed securities	0	0
Corporate debt securities	0	0
Government agency collateralized mortgage obligations	0	0
Marketable equity securities	426,000	445,000
Total available-for-sale investment securities	1,676,538,000	1,497,112,000
Mortgages loans held for sale	0	0
Commitments to originate real estate loans for sale	0	0
Forward sales commitments	0	0
Total	1,676,538,000	1,497,112,000
Recurring [Member] \| Level 2 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	0	21,066,000
Obligations of state and political subdivisions	672,709,000	671,903,000
Government agency mortgage-backed securities	229,526,000	237,728,000
Corporate debt securities	27,026,000	27,091,000
Government agency collateralized mortgage obligations	16,980,000	18,025,000
Marketable equity securities	0	0
Total available-for-sale investment securities	946,241,000	975,813,000
Mortgages loans held for sale	1,437,000	1,042,000
Commitments to originate real estate loans for sale	0	0
Forward sales commitments	(22,000)	(43,000)
Total	947,656,000	976,812,000
Mortgage loans held for sale, at principal value	1,400,000
Mortgage loans held for sale, unrealized gains (losses)	52,000
Recurring [Member] \| Level 3 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	0	0
Obligations of state and political subdivisions	0	0
Government agency mortgage-backed securities	0	0
Corporate debt securities	0	0
Government agency collateralized mortgage obligations	0	0
Marketable equity securities	0	0
Total available-for-sale investment securities	0	0
Mortgages loans held for sale	0	0
Commitments to originate real estate loans for sale	152,000	185,000
Forward sales commitments	0	0
Total	152,000	185,000
Non-recurring [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Other real estate owned	1,767,000	1,855,000
Non-recurring [Member] \| Level 1 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Other real estate owned	0	0
Non-recurring [Member] \| Level 2 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Other real estate owned	0	0
Non-recurring [Member] \| Level 3 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Other real estate owned	$ 1,767,000	$ 1,855,000

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents debt securities issued by corporations.

No definition available.