SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	$ 1,067,142	$ 675,474
Gross Unrealized Gains	18,822	11,701
Gross Unrealized (Losses)	(7,265)	(9,827)
Total securities available for sale, Estimated Fair Value	1,078,699	677,348	583,217
US Government Agencies Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	1,552	1,654
Gross Unrealized Gains	1,622	499
Gross Unrealized (Losses)
Total securities available for sale, Estimated Fair Value	3,174	2,153
Obligations of States and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	427,388	255,335
Gross Unrealized Gains	10,346	6,107
Gross Unrealized (Losses)	(4,083)	(6,612)
Total securities available for sale, Estimated Fair Value	433,651	254,830
Corporate and Other Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	72,881	9,479
Gross Unrealized Gains	262	115
Gross Unrealized (Losses)	(521)	(160)
Total securities available for sale, Estimated Fair Value	72,622	9,434
Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	552,000	405,389
Gross Unrealized Gains	6,564	4,954
Gross Unrealized (Losses)	(2,601)	(2,981)
Total securities available for sale, Estimated Fair Value	555,963	407,362
Other Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	13,321	3,617
Gross Unrealized Gains	28	26
Gross Unrealized (Losses)	(60)	(74)
Total securities available for sale, Estimated Fair Value	$ 13,289	$ 3,569