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, 2015	Dec. 31, 2014
Amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities
Amortized Cost	$ 1,057,159	$ 1,075,235
Gross Unrealized Gains	33,898	28,737
Gross Unrealized (Losses)	(1,393)	(1,858)
Total securities available for sale, Estimated Fair Value	1,089,664us-gaap_AvailableForSaleSecurities	1,102,114us-gaap_AvailableForSaleSecurities
US Government Agencies Debt Securities [Member]
Amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities
Amortized Cost	8,236	8,313
Gross Unrealized Gains	359	166
Gross Unrealized (Losses)		(25)
Total securities available for sale, Estimated Fair Value	8,595	8,454
Obligations of States and Political Subdivisions [Member]
Amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities
Amortized Cost	431,355	427,483
Gross Unrealized Gains	21,594	18,885
Gross Unrealized (Losses)	(511)	(721)
Total securities available for sale, Estimated Fair Value	452,438	445,647
Corporate and Other Securities [Member]
Amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities
Amortized Cost	78,400	78,744
Gross Unrealized Gains	169	244
Gross Unrealized (Losses)	(428)	(308)
Total securities available for sale, Estimated Fair Value	78,141	78,680
Mortgage Backed Securities [Member]
Amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities
Amortized Cost	529,188	550,716
Gross Unrealized Gains	11,729	9,411
Gross Unrealized (Losses)	(454)	(798)
Total securities available for sale, Estimated Fair Value	540,463	559,329
Other Securities [Member]
Amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities
Amortized Cost	9,980	9,979
Gross Unrealized Gains	47	31
Gross Unrealized (Losses)		(6)
Total securities available for sale, Estimated Fair Value	$ 10,027	$ 10,004

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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