SECURITIES - Contractual Maturities of Securities Available for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available for Sale, Amortized Cost
Within one year	$ 18,434
One through five years	89,659
Six through ten years	97,431
After ten years	176,057
Equity securities	4,670
Amortized Cost	1,072,250	$ 1,002,803
Available for Sale, Fair Value
Within one year	18,666
One through five years	93,452
Six through ten years	101,640
After ten years	180,492
Equity securities	4,670
Fair Value	1,083,903	1,007,540
Mortgage-backed securities-residential (Government Sponsored Entity)
Available for Sale, Amortized Cost
Debt securities without single maturity date	402,987
Amortized Cost	402,987	450,006
Available for Sale, Fair Value
Debt securities without single maturity date	402,226
Fair Value	402,226	446,630
Collateralized mortgage obligations (Government Sponsored Entity)
Available for Sale, Amortized Cost
Debt securities without single maturity date	283,012
Amortized Cost	283,012	179,314
Available for Sale, Fair Value
Debt securities without single maturity date	282,757
Fair Value	$ 282,757	$ 179,401