SECURITIES - Amortized Cost and Fair Value of Securities Available for Sale and Held for Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	$ 997,155	$ 960,809
Gross Unrealized Gains, Available for Sale	6,902	3,767
Gross Unrealized Losses, Available for Sale	(7,258)	(14,073)
Fair Value, Available for Sale	996,799	950,503
Gross Amortized Cost, Held for Investment Securities	374,773	372,498
Gross Unrealized Gains, Held for Investment Securities	2,746	1,753
Gross Unrealized Losses, Held for Investment Securities	(2,558)	(4,370)
Fair Value, Held for Investment Securities	374,961	369,881
U.S. Treasury Securities and obligations of U.S. Government Sponsored Entities [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	9,830	12,073
Gross Unrealized Gains, Available for Sale	310	255
Gross Unrealized Losses, Available for Sale	0	0
Fair Value, Available for Sale	10,140	12,328
Mortgage-backed securities of U.S. Government Sponsored Entities [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	284,015	287,726
Gross Unrealized Gains, Available for Sale	1,245	585
Gross Unrealized Losses, Available for Sale	(2,298)	(4,823)
Fair Value, Available for Sale	282,962	283,488
Gross Amortized Cost, Held for Investment Securities	179,437	159,941
Gross Unrealized Gains, Held for Investment Securities	1,403	704
Gross Unrealized Losses, Held for Investment Securities	(996)	(1,243)
Fair Value, Held for Investment Securities	179,844	159,402
Collateralized Mortgage Obligations Of US Government Sponsored Entities [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	232,278	238,805
Gross Unrealized Gains, Available for Sale	525	314
Gross Unrealized Losses, Available for Sale	(4,001)	(5,065)
Fair Value, Available for Sale	228,802	234,054
Gross Amortized Cost, Held for Investment Securities	126,849	147,208
Gross Unrealized Gains, Held for Investment Securities	462	386
Gross Unrealized Losses, Held for Investment Securities	(1,506)	(2,630)
Fair Value, Held for Investment Securities	125,805	144,964
Commercial mortgage backed securities of U.S. Government Sponsored Entities [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	22,274	22,351
Gross Unrealized Gains, Available for Sale	355	222
Gross Unrealized Losses, Available for Sale	(10)	(28)
Fair Value, Available for Sale	22,619	22,545
Gross Amortized Cost, Held for Investment Securities	17,441	17,375
Gross Unrealized Gains, Held for Investment Securities	645	233
Gross Unrealized Losses, Held for Investment Securities	0	(74)
Fair Value, Held for Investment Securities	18,086	17,534
Private mortgage backed securities [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	32,928	32,780
Gross Unrealized Gains, Available for Sale	925	0
Gross Unrealized Losses, Available for Sale	0	(791)
Fair Value, Available for Sale	33,853	31,989
Fair Value, Held for Investment Securities	0
Private collateralized mortgage obligations [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	50,725	67,542
Gross Unrealized Gains, Available for Sale	682	563
Gross Unrealized Losses, Available for Sale	(302)	(816)
Fair Value, Available for Sale	51,105	67,289
Gross Amortized Cost, Held for Investment Securities	5,608	6,427
Gross Unrealized Gains, Held for Investment Securities	8	0
Gross Unrealized Losses, Held for Investment Securities	(56)	(109)
Fair Value, Held for Investment Securities	5,560	6,318
Collateralized loan obligations [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	207,341	124,716
Gross Unrealized Gains, Available for Sale	794	838
Gross Unrealized Losses, Available for Sale	(18)	(665)
Fair Value, Available for Sale	208,117	124,889
Gross Amortized Cost, Held for Investment Securities	45,438	41,547
Gross Unrealized Gains, Held for Investment Securities	228	430
Gross Unrealized Losses, Held for Investment Securities	0	(314)
Fair Value, Held for Investment Securities	45,666	41,663
Obligations of state and political subdivisions [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	59,495	63,161
Gross Unrealized Gains, Available for Sale	1,065	622
Gross Unrealized Losses, Available for Sale	(375)	(895)
Fair Value, Available for Sale	60,185	62,888
Corporate and other debt securities [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	70,083	74,121
Gross Unrealized Gains, Available for Sale	803	257
Gross Unrealized Losses, Available for Sale	(89)	(517)
Fair Value, Available for Sale	70,797	73,861
Fair Value, Held for Investment Securities	0
Private commercial mortgage backed securities [Member]
Amortized cost and fair value of securities available for sale and held for investment
Gross Amortized Cost, Available for Sale	28,186	37,534
Gross Unrealized Gains, Available for Sale	198	111
Gross Unrealized Losses, Available for Sale	(165)	(473)
Fair Value, Available for Sale	28,219	$ 37,172
Fair Value, Held for Investment Securities	$ 0