FAIR VALUE DISCLOSURES (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2012 Carrying Value [Member]	Dec. 31, 2011 Carrying Value [Member]	Dec. 31, 2012 Fair Value [Member]	Dec. 31, 2011 Fair Value [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 1 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Level 1 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 2 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Level 2 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Level 3 [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2011 Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Gains (Losses) [Member]	Dec. 31, 2011 Fair Value, Measurements, Nonrecurring [Member] Gains (Losses) [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 1 [Member]	Dec. 31, 2011 Fair Value, Measurements, Nonrecurring [Member] Level 1 [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 2 [Member]	Dec. 31, 2011 Fair Value, Measurements, Nonrecurring [Member] Level 2 [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 3 [Member]	Dec. 31, 2011 Fair Value, Measurements, Nonrecurring [Member] Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative interest rate (in hundredths)		1.60%	4.50%
Available-for-sale securities [Abstract]
U.S. Government agencies								$ 1,401,996	$ 1,501,243	$ 0	$ 0	$ 1,401,996	$ 1,501,243	$ 0	$ 0
Government agency issued residential mortgage-backed securities								366,875	404,610	0	0	366,875	404,610	0	0
Government agency issued commercial mortgage-backed securities								91,445	34,599	0	0	91,445	34,599	0	0
Obligations of states and political subdivisions								565,873	563,520	0	0	565,873	563,520	0	0
Collateralized debt obligations								0	0	0	0	0	0	0	0
Other								7,843	9,546	744	561	7,099	8,985	0	0
Mortgage servicing rights								37,882	30,174	0	0	0	0	37,882	30,174
Derivative instruments								55,684	55,749	0	0	0	0	55,684	55,749
Total								2,527,598	2,599,441	744	561	2,433,288	2,512,957	93,566	85,923
Liabilities [Abstract]
Derivative instruments								52,773	55,407	0		0		52,773	55,407
Percentage rate deduction to determine the fair value of other real estate owned (in hundredths)	7.00%
Assets [Abstract]
Loans held for sale				129,138	83,458	129,230	83,503									129,138	83,458	0	0	0	0	129,138	83,458	0	0
Impaired loans																156,728	234,923	(10,541)	(39,708)	0	0	0	0	156,728	234,923
Other real estate owned																$ 103,248	$ 173,805	$ (31,055)	$ (21,641)	$ 0	$ 0	$ 0	$ 0	$ 103,248	$ 173,805