FAIR VALUE DISCLOSURES (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage rate deduction to determine the fair value of other real estate owned (in hundredths)	7.00%
Available-for-sale securities [Abstract]
Mortgage servicing rights	$ 53,759	$ 54,662	$ 51,025	$ 37,882
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative interest rate	1.51%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative interest rate	3.66%
Carrying Value [Member]
Available-for-sale securities [Abstract]
Loans held for sale ($137,005 at fair value at September 30, 2014	137,005	69,593
Fair Value [Member]
Available-for-sale securities [Abstract]
Loans held for sale ($137,005 at fair value at September 30, 2014	137,005	70,063
Fair Value, Measurements, Recurring [Member]
Available-for-sale securities [Abstract]
U.S. Government agencies	1,238,088		1,519,459
Government agency issued residential mortgage-backed securities	218,748		268,367
Government agency issued commercial mortgage-backed securities	237,325		229,412
Obligations of states and political subdivisions	509,304		528,889
Other	7,997		8,029
Mortgage servicing rights	53,759		51,025
Derivative instruments	23,884		35,004
Loans held for sale ($137,005 at fair value at September 30, 2014	137,005
Total	2,426,110		2,640,185
Liabilities [Abstract]
Derivative instruments	22,470		35,386
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Available-for-sale securities [Abstract]
Other	1,094		1,048
Total	1,094		1,048
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Available-for-sale securities [Abstract]
U.S. Government agencies	1,238,088		1,519,459
Government agency issued residential mortgage-backed securities	218,748		268,367
Government agency issued commercial mortgage-backed securities	237,325		229,412
Obligations of states and political subdivisions	509,304		528,889
Other	6,903		6,981
Loans held for sale ($137,005 at fair value at September 30, 2014	137,005
Total	2,347,373		2,553,108
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Available-for-sale securities [Abstract]
Mortgage servicing rights	53,759		51,025
Derivative instruments	23,884		35,004
Total	77,643		86,029
Liabilities [Abstract]
Derivative instruments	22,470		35,386
Fair Value, Measurements, Nonrecurring [Member]
Available-for-sale securities [Abstract]
Loans held for sale ($137,005 at fair value at September 30, 2014			77,114
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member]
Available-for-sale securities [Abstract]
Loans held for sale ($137,005 at fair value at September 30, 2014
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
Available-for-sale securities [Abstract]
Loans held for sale ($137,005 at fair value at September 30, 2014			$ 77,114