INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Available-for-Sale Portfolio [Abstract]
Amortized Cost	$ 2,737,644	$ 2,742,278
Gross Unrealized Gains	133,655	69,254
Gross Unrealized Losses	563	3,419
Fair Value	2,870,736	2,808,113
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized Cost	2,737,393
Fair Value	2,870,326
Other Securities [Abstract]
Amortized Cost	32,142	39,827
Fair Value	32,142	39,827
U.S. Treasury and Agency Obligations [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized Cost	1,868,429	1,866,819
Gross Unrealized Gains	95,114	35,186
Gross Unrealized Losses	0	2,027
Fair Value	1,963,543	1,899,978
Obligations of State and Political Subdivisions [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized Cost	632,114	640,455
Gross Unrealized Gains	30,283	26,487
Gross Unrealized Losses	5	59
Fair Value	662,392	666,883
Government Agency Mortgage-Backed Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized Cost	208,300	205,220
Gross Unrealized Gains	7,500	6,906
Gross Unrealized Losses	529	1,261
Fair Value	215,271	210,865
Corporate Debt Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized Cost	16,639	16,672
Gross Unrealized Gains	55	66
Gross Unrealized Losses	10	58
Fair Value	16,684	16,680
Government Agency Collateralized Mortgage Obligations [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized Cost	11,911	12,862
Gross Unrealized Gains	525	446
Gross Unrealized Losses	0	0
Fair Value	12,436	13,308
Marketable Equity Securities [Member]
Available For Sale Equity Securities Amortized Cost Basis [Abstract]
Amortized Cost	251	250
Gross Unrealized Gains	178	163
Gross Unrealized Losses	19	14
Fair Value	410	399
Federal Home Loan Bank Common Stock [Member]
Other Securities [Abstract]
Amortized Cost	7,258	19,317
Fair Value	7,258	19,317
Federal Reserve Bank Common Stock [Member]
Other Securities [Abstract]
Amortized Cost	20,663	16,050
Fair Value	20,663	16,050
Other Equity Securities [Member]
Other Securities [Abstract]
Amortized Cost	4,221	4,460
Fair Value	$ 4,221	$ 4,460