GOODWILL, CORE DEPOSIT PREMIUM AND OTHER INTANGIBLE ASSETS (Carrying amount of intangible assets (incl accumulated amortization) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 110,229	$ 133,879
Accumulated Amortization	50,331	55,328
Net Carrying Amount	59,898	78,551
Core deposit intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	95,033	83,640
Accumulated Amortization	42,539	36,403
Net Carrying Amount	52,494	47,237
Customer relationship intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,177	1,177
Accumulated Amortization	953	935
Net Carrying Amount	224	242
Mortgage servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,112	42,228
Accumulated Amortization	1,311	12,865
Net Carrying Amount	5,801	29,363
Commercial servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,907	6,834
Accumulated Amortization	5,528	5,125
Net Carrying Amount	$ 1,379	$ 1,709