BUSINESS COMBINATION BUSINESS COMBINATIONS (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
	Apr. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Cash consideration		$ 43
Stock consideration		1,045,876
Warrant consideration		14,460
Options consideration		1,577
Total purchase consideration	$ 1,100,000	1,061,956
Cash		71,734
Investment securities available-for-sale		901,008
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Held to Maturity Securities		171,423
Other investments		28,763
Loans		2,792,517
Premises and equipment		98,537
Intangible assets		42,887
Other assets		169,311
Assets held for sale		127,775
Total assets acquired		4,403,955
Deposits		3,264,038
Subordinated notes		49,027
FHLB advances		291,887
Other borrowings		205,620
Other liabilities		32,654
Liabilities held for sale		175,722
Total liabilities assumed		4,018,948	$ 0
Net identifiable assets		385,007
Goodwill		$ 676,949	$ 0	$ 0