SECURITIES - Securities in an Unrealized Loss Position (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Securities in a continuous unrealized loss position with unrealized losses presented by length of time
Less than 12 months, Fair Value	$ 307,957	$ 509,184
Less than 12 months, Unrealized Losses	(2,714)	(8,679)
12 months or longer, Fair Value	208,148	8,518
12 months or longer, Unrealized Losses	(4,970)	(225)
Total Fair Value	516,105	517,702
Total Unrealized Losses	$ (7,684)	(8,904)
Other-Than-Temporary-Impairment
Number of general segments segregated in investment securities portfolio | item	2
Number of security in the portfolio | item	1,019
Number of portfolio security in unrealized loss position | item	162
Decline in fair value of security attributable to change in interest rates and illiquidity	$ 3,792
State and municipal
Securities in a continuous unrealized loss position with unrealized losses presented by length of time
Less than 12 months, Fair Value	12,486	95,822
Less than 12 months, Unrealized Losses	(46)	(2,848)
12 months or longer, Fair Value	22,537
12 months or longer, Unrealized Losses	(396)
Total Fair Value	35,023	95,822
Total Unrealized Losses	(442)	(2,848)
Mortgage-backed securities-residential (Government Sponsored Entity)
Securities in a continuous unrealized loss position with unrealized losses presented by length of time
Less than 12 months, Fair Value	112,127	335,668
Less than 12 months, Unrealized Losses	(737)	(4,629)
12 months or longer, Fair Value	132,168
12 months or longer, Unrealized Losses	(3,055)
Total Fair Value	244,295	335,668
Total Unrealized Losses	(3,792)	(4,629)
Collateralized mortgage obligations (Government Sponsored Entity)
Securities in a continuous unrealized loss position with unrealized losses presented by length of time
Less than 12 months, Fair Value	183,344	77,694
Less than 12 months, Unrealized Losses	(1,931)	(1,202)
12 months or longer, Fair Value	53,443	8,518
12 months or longer, Unrealized Losses	(1,519)	(225)
Total Fair Value	236,787	86,212
Total Unrealized Losses	(3,450)	$ (1,427)
Other-Than-Temporary-Impairment
Other than temporary impairment on available for sale securities	$ 0