Goodwill, Core Deposit Premium and Other Intangible Assets (Estimated future amortization expense for amortizable intangible assets) (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2018	$ 4,374
Year ending December 31,
2019	17,107
2020	14,759
2021	12,496
2022	10,014
2023	8,178
Thereafter	15,182
Total	82,110
Core deposit intangibles
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2018	2,583
Year ending December 31,
2019	9,452
2020	8,230
2021	7,036
2022	5,634
2023	4,933
Thereafter	11,951
Total	49,819
Customer relationship intangibles
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2018	10
Year ending December 31,
2019	38
2020	37
2021	35
2022	34
2023	34
Thereafter	64
Total	252
Mortgage servicing rights
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2018	1,642
Year ending December 31,
2019	7,132
2020	6,113
2021	5,094
2022	4,076
2023	3,057
Thereafter	3,057
Total	30,171
Commercial servicing rights
Future amortization expense for amortizable intangible assets [Line Items]
Three months ending December 31, 2018	139
Year ending December 31,
2019	485
2020	379
2021	331
2022	270
2023	154
Thereafter	110
Total	$ 1,868