INVESTMENTS - Summary of Held-To-Maturity and Available-For-Sale Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	$ 890,806	$ 837,272
Held To Maturity Gross Unrealized Gain Accumulated In Investments	3,714	1,772
Held To Maturity Securities Gross Unrealized Loss Accumulated In Investments	(9,193)	(14,059)
Held-to-Maturity Market Value	885,327	824,985
Available-for-Sale Amortized Cost	887,692	945,052
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	5,517	5,645
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(30,683)	(37,096)
Available-for-Sale Market Value	862,526	913,601
U.S. Treasuries
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	0	0
Held To Maturity Gross Unrealized Gain Accumulated In Investments	0	0
Held To Maturity Securities Gross Unrealized Loss Accumulated In Investments	0	0
Held-to-Maturity Market Value	0	0
Available-for-Sale Amortized Cost	97	97
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(4)	(7)
Available-for-Sale Market Value	93	90
Securities of U.S. government agencies and corporations
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	18,603	18,981
Held To Maturity Gross Unrealized Gain Accumulated In Investments	0	0
Held To Maturity Securities Gross Unrealized Loss Accumulated In Investments	(535)	(791)
Held-to-Maturity Market Value	18,068	18,190
Available-for-Sale Amortized Cost	9,978	9,980
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(249)	(404)
Available-for-Sale Market Value	9,729	9,576
Mortgage-backed securities
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	829,311	775,025
Held To Maturity Gross Unrealized Gain Accumulated In Investments	2,906	1,337
Held To Maturity Securities Gross Unrealized Loss Accumulated In Investments	(7,924)	(12,229)
Held-to-Maturity Market Value	824,293	764,133
Available-for-Sale Amortized Cost	696,800	678,267
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	4,862	5,372
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(24,414)	(28,593)
Available-for-Sale Market Value	677,248	655,046
Obligations of state and other political subdivisions
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	25,512	25,788
Held To Maturity Gross Unrealized Gain Accumulated In Investments	195	152
Held To Maturity Securities Gross Unrealized Loss Accumulated In Investments	(734)	(1,039)
Held-to-Maturity Market Value	24,973	24,901
Available-for-Sale Amortized Cost	31,121	33,410
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	9	10
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(2,606)	(3,097)
Available-for-Sale Market Value	28,524	30,323
Asset-backed Securities [Member]
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	0	0
Held To Maturity Gross Unrealized Gain Accumulated In Investments	0	0
Held To Maturity Securities Gross Unrealized Loss Accumulated In Investments	0	0
Held-to-Maturity Market Value	0	0
Available-for-Sale Amortized Cost	49,529	114,209
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	1	1
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(100)	(616)
Available-for-Sale Market Value	49,430	113,594
Other securities
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	17,380	17,478
Held To Maturity Gross Unrealized Gain Accumulated In Investments	613	283
Held To Maturity Securities Gross Unrealized Loss Accumulated In Investments	0	0
Held-to-Maturity Market Value	17,993	17,761
Available-for-Sale Amortized Cost	100,167	109,089
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	645	262
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(3,310)	(4,379)
Available-for-Sale Market Value	$ 97,502	$ 104,972