Goodwill, Core Deposit Premium and Other Intangible Assets (Carrying amount of intangible assets (incl accumulated amortization) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 97,569	$ 89,724
Accumulated Amortization	36,149	32,779
Net Carrying Amount	61,420	56,945
Core deposit intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	43,504	37,118
Accumulated Amortization	17,345	15,460
Net Carrying Amount	26,159	21,658
Mortgage servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	46,818	45,744
Accumulated Amortization	16,368	15,430
Net Carrying Amount	30,450	30,314
Customer relationship intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,176	1,177
Accumulated Amortization	825	815
Net Carrying Amount	351	362
Commercial servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,071	5,685
Accumulated Amortization	1,611	1,074
Net Carrying Amount	$ 4,460	$ 4,611