GOODWILL, CORE DEPOSIT PREMIUM AND OTHER INTANGIBLE ASSETS (Estimated future amortization expense for amortizable intangible assets) (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2019	$ 3,478
Year ending December 31,
2020	11,643
2021	9,747
2022	7,986
2023	6,860
2024	5,552
Thereafter	10,824
Total	56,090
Core Deposit Intangibles
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2019	2,908
Year ending December 31,
2020	10,159
2021	8,462
2022	6,898
2023	6,019
2024	4,945
Thereafter	10,214
Total	49,605
Customer Relationship Intangibles
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2019	9
Year ending December 31,
2020	36
2021	35
2022	35
2023	34
2024	33
Thereafter	32
Total	214
Mortgage Servicing Rights
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2019	472
Year ending December 31,
2020	1,137
2021	975
2022	813
2023	649
2024	488
Thereafter	488
Total	5,022
Commercial Servicing Rights
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2019	89
Year ending December 31,
2020	311
2021	275
2022	240
2023	158
2024	86
Thereafter	90
Total	$ 1,249