Goodwill, Core Deposit Premium and Other Intangible Assets (Estimated future amortization expense for amortizable intangible assets) (Details) $ in Thousands	Jun. 30, 2018 USD ($)
Future amortization expense for amortizable intangible assets [Line Items]
Six months ending December 31, 2018	$ 8,525
Year ending December 31,
2019	16,720
2020	14,429
2021	12,223
2022	9,796
2023	8,012
Thereafter	14,989
Total	84,694
Core deposit intangibles
Future amortization expense for amortizable intangible assets [Line Items]
Six months ending December 31, 2018	5,199
Year ending December 31,
2019	9,452
2020	8,230
2021	7,036
2022	5,634
2023	4,934
Thereafter	11,951
Total	52,436
Customer relationship intangibles
Future amortization expense for amortizable intangible assets [Line Items]
Six months ending December 31, 2018	19
Year ending December 31,
2019	38
2020	37
2021	35
2022	35
2023	34
Thereafter	64
Total	262
Mortgage servicing rights
Future amortization expense for amortizable intangible assets [Line Items]
Six months ending December 31, 2018	3,015
Year ending December 31,
2019	6,735
2020	5,773
2021	4,811
2022	3,849
2023	2,886
Thereafter	2,886
Total	29,955
Commercial servicing rights
Future amortization expense for amortizable intangible assets [Line Items]
Six months ending December 31, 2018	292
Year ending December 31,
2019	495
2020	389
2021	341
2022	278
2023	158
Thereafter	88
Total	$ 2,041