Goodwill, Core Deposit Premium and Other Intangible Assets (Carrying amount of intangible assets (incl accumulated amortization) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 134,232	$ 112,043
Accumulated Amortization	52,122	50,983
Net Carrying Amount	82,110	61,060
Core deposit intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	83,639	62,008
Accumulated Amortization	33,820	27,086
Net Carrying Amount	49,819	34,922
Customer relationship intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,177	1,177
Accumulated Amortization	925	896
Net Carrying Amount	252	281
Mortgage servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	42,616	42,139
Accumulated Amortization	12,445	18,891
Net Carrying Amount	30,171	23,248
Commercial servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,800	6,719
Accumulated Amortization	4,932	4,110
Net Carrying Amount	$ 1,868	$ 2,609