INVESTMENTS - Summary of Held-To-Maturity and Available-For-Sale Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Total	$ 756,035	$ 867,996
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	15,438	9,112
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(961)	(2,359)
Held-to-Maturity Market Value	770,512	874,749
Total	1,071,558	849,504
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	8,739	6,760
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(10,630)	(15,796)
Investment securities available-for-sale	1,069,667	840,468
U.S. Treasuries
Investment Holdings [Line Items]
Total	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-Maturity Market Value	0	0
Total	98	97
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	1	0
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Investment securities available-for-sale	99	97
Securities of U.S. government agencies and corporations
Investment Holdings [Line Items]
Total	15,968	17,570
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	222	24
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	(23)
Held-to-Maturity Market Value	16,190	17,571
Total	8,717	11,814
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	247	67
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	0	(1)
Investment securities available-for-sale	8,964	11,880
Mortgage-backed securities
Investment Holdings [Line Items]
Total	707,124	801,465
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	15,048	7,813
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(520)	(2,064)
Held-to-Maturity Market Value	721,652	807,214
Total	660,881	611,497
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	5,040	4,462
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(6,879)	(13,211)
Investment securities available-for-sale	659,042	602,748
Obligations of state and other political subdivisions
Investment Holdings [Line Items]
Total	28,138	44,164
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	168	1,275
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(317)	(193)
Held-to-Maturity Market Value	27,989	45,246
Total	75,845	73,649
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	2,311	883
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(928)	(947)
Investment securities available-for-sale	77,228	73,585
Asset-backed Securities [Member]
Investment Holdings [Line Items]
Total	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-Maturity Market Value	0	0
Total	215,036	74,784
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	221	155
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(1,801)	(103)
Investment securities available-for-sale	213,456	74,836
Other securities
Investment Holdings [Line Items]
Total	4,805	4,797
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(124)	(79)
Held-to-Maturity Market Value	4,681	4,718
Total	110,981	77,663
Available for Sale Securities Gross Unrealized Gain Accumulated In Investments	919	1,193
Available for Sale Securities Gross Unrealized Loss Accumulated In Investments	(1,022)	(1,534)
Investment securities available-for-sale	$ 110,878	$ 77,322