Goodwill, Core Deposit Premium and Other Intangible Assets (Carrying amount of intangible assets (incl accumulated amortization) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 37,804	$ 35,737
Accumulated Amortization	17,538	17,251
Net Carrying Amount	20,266	18,486
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	11,668	11,668
Accumulated Amortization	9,515	9,327
Net Carrying Amount	2,153	2,341
Mortgage Servicing Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,959	22,892
Accumulated Amortization	7,326	7,239
Net Carrying Amount	17,633	15,653
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,177	1,177
Accumulated Amortization	697	685
Net Carrying Amount	$ 480	$ 492