SECURITIES - Contractual Maturities of Securities Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available for Sale, Amortized Cost
Amortized Cost, Within one year	$ 23,895
Amortized Cost, One through five years	89,897
Amortized Cost, Six through ten years	89,513
Amortized Cost, After ten years	187,591
Amortized Cost, Equity securities	4,670
Amortized Cost	1,071,107	$ 1,002,803
Fair Value, Within one year	24,200
Fair Value, One through five years	92,721
Fair Value, Six through ten years	92,961
Fair Value, After ten years	193,372
Fair Value, Equity securities	4,670
Fair Value	1,077,573	1,007,540
Mortgage-backed securities-residential (Government Sponsored Entity)
Available for Sale, Amortized Cost
Amortized Cost	386,116	450,006
Fair Value	383,254	446,630
Collateralized mortgage obligations (Government Sponsored Entity)
Available for Sale, Amortized Cost
Amortized Cost	289,425	179,314
Fair Value	$ 286,395	$ 179,401