Goodwill, Core Deposit Premium and Other Intangible Assets (Mortgage loans servicing) (Details) (USD $)					3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Mortgage Servicing Rights 15-year Tranche [Member]	Dec. 31, 2012 Mortgage Servicing Rights 15-year Tranche [Member]	Mar. 31, 2013 Mortgage Servicing Rights 30-year Tranche [Member]	Dec. 31, 2012 Mortgage Servicing Rights 30-year Tranche [Member]
Goodwill and Intangible Assets Disclosure [Abstract]
Mortgage loans serviced for others	$ 2,350,000,000	$ 2,200,000,000
Valuation allowance	0	496,000
Valuation servicing rights in tranches [Line Items]
Servicing asset at amortized value	19,400,000	16,000,000			3,700,000	3,300,000	15,700,000	12,600,000
Servicing asset, agreement term					15 years	15 years	30 years
Servicing asset at amortized cost	$ 17,633,000	$ 15,653,000	$ 11,556,000	$ 11,276,000	$ 3,100,000	$ 3,000,000	$ 14,500,000	$ 12,600,000