GOODWILL, CORE DEPOSIT PREMIUM AND OTHER INTANGIBLE ASSETS (Carrying amount of intangible assets (incl accumulated amortization) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 110,730	$ 133,879
Accumulated Amortization	54,640	55,328
Net Carrying Amount	56,090	78,551
Core deposit intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	95,033	83,640
Accumulated Amortization	45,428	36,403
Net Carrying Amount	49,605	47,237
Customer relationship intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,177	1,177
Accumulated Amortization	963	935
Net Carrying Amount	214	242
Mortgage servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,584	42,228
Accumulated Amortization	2,562	12,865
Net Carrying Amount	5,022	29,363
Commercial servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,936	6,834
Accumulated Amortization	5,687	5,125
Net Carrying Amount	$ 1,249	$ 1,709