SECURITIES - Narrative (Details)		12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Investment [Line Items]
Transferred Securities, Unrealized Loss, Before Tax		$ 15,300,000	$ 17,400,000
Securities transferred, Unrealized Loss, Net of Tax		12,100,000	13,800,000
Fair value of securities transferred from AFS to HTM		0	0	$ 157,083,000
Securities available for sale, at estimated fair value		1,989,436,000
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12		$ 11,881,000	0	0
AFS securities and HTM securities with other-than-temporary impairment		0
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Net realized (loss) gain on AFS securities		$ (1,800,000)
Gross realized gains on AFS securities		2,000,000
Gross realized loss on AFS securities		3,800,000
Net realized (loss) gain on AFS securities			625,000	2,800,000
Gross realized gains on AFS securities			5,000,000	6,300,000
Gross realized loss on AFS securities			4,400,000	3,400,000
Carrying value of investment securities pledged as collateral		1,080,000,000	1,240,000,000
Equity investments		$ 12,093,000
Equity investments without readily determinable fair value			5,821,000
Securities available for sale, at estimated fair value			1,538,755,000
Equity investments with other-than-temporary impairment		0
Proceeds from sale of held-to-maturity securities		$ 0	0	$ 0
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2017-12
Investment [Line Items]
Securities available for sale, at estimated fair value	$ 743,400,000
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	11,900,000
Unrealized net gain on securities transferred from held to maturity to available for sale, net of tax	$ 9,400,000
Other Equity Securities
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Securities available for sale, at estimated fair value			5,920,000
Unrealized losses on equity investment included in AFS securities			$ 85,000