BUSINESS COMBINATIONS - fair value of acquired loans (Details) - USD ($) $ in Thousands	Apr. 07, 2017	Jun. 03, 2016	Mar. 11, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net			$ 280,022
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value			266,137
Commercial Real Estate [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net			172,531
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value			167,105
Commercial Loan [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net			39,070
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value			37,804
Single Family Residential Real Estate [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net			38,304
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value			37,367
Construction Development Land [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net			20,546
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value			18,108
Consumer And Other Loans [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net			3,385
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value			3,110
Purchased Credit Impaired [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net			6,186
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value			$ 2,643
BMO Harris Bank [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net		$ 64,043
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value		62,671
BMO Harris Bank [Member] | Commercial Real Estate [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net		31,564
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value		31,200
BMO Harris Bank [Member] | Commercial Loan [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net		32,479
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value		31,471
BMO Harris Bank [Member] | Purchased Credit Impaired [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net		0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value		$ 0
Gulf Shore Banc shares Inc [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	$ 256,876
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	250,884
Gulf Shore Banc shares Inc [Member] | Commercial Real Estate [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	106,729
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	103,908
Gulf Shore Banc shares Inc [Member] | Commercial Loan [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	32,137
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	32,252
Gulf Shore Banc shares Inc [Member] | Single Family Residential Real Estate [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	101,281
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	99,598
Gulf Shore Banc shares Inc [Member] | Construction Development Land [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	13,175
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	11,653
Gulf Shore Banc shares Inc [Member] | Consumer And Other Loans [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	3,554
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	3,473
Gulf Shore Banc shares Inc [Member] | Purchased Credit Impaired [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	$ 0