Fair Value (Quantitative Information About Level 3 Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified																			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Level 3	Dec. 31, 2012 Recurring Basis Level 3	Dec. 31, 2011 Recurring Basis Level 3	Dec. 31, 2012 Nonrecurring Basis Level 3		Dec. 31, 2011 Nonrecurring Basis Level 3	Dec. 31, 2012 Agricultural and Agricultural Real Estate Nonrecurring Basis Level 3		Dec. 31, 2012 Residential Real Estate Nonrecurring Basis Level 3		Dec. 31, 2012 Consumer Nonrecurring Basis Level 3		Dec. 31, 2012 Commercial Nonrecurring Basis Level 3		Dec. 31, 2012 Commercial Real Estate Commercial Nonrecurring Basis Level 3		Dec. 31, 2012 Z-Tranche Securities Recurring Basis Level 3	Dec. 31, 2012 Z-Tranche Securities Weighted Average Recurring Basis Level 3	Dec. 31, 2012 Z-Tranche Securities Minimum Recurring Basis Level 3	Dec. 31, 2012 Z-Tranche Securities Maximum Recurring Basis Level 3	Dec. 31, 2012 Mortgage Servicing Rights Weighted Average Recurring Basis Level 3	Dec. 31, 2012 Mortgage Servicing Rights Minimum Recurring Basis Level 3	Dec. 31, 2012 Mortgage Servicing Rights Maximum Recurring Basis Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	$ 1,506,075	$ 4,340	$ 4,340	$ 3,243														$ 4,340
Collateral dependent impaired loans					78,952		94,961	16,019	[1]	6,660	[1]	4,121	[1]	7,681	[1]	44,471	[1]
Other real estate owned					35,822	[1]	44,387
Mortgage servicing rights					$ 15,956		$ 11,505
Pretax discount rate																				8.00%	10.00%
Actual defaults																			15.52%	13.94%	20.94%
Actual deferrals																			11.32%	6.30%	23.71%	18.05%	12.99%	18.71%

[1] Not Meaningful. Third party appraisals are obtained as to the value of the underlying asset, but disclosure of this information would not provide meaningful information, as the range will vary widely from loan to loan. Types of discounts considered included age of the appraisal, local market conditions, current condition of the property, and estimated sales costs. These discounts will also vary from loan to loan, thus providing range would not be meaningful.