Shareholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																				1 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2013 Accumulated Net Unrealized Gain (Loss) on Available for Sale Securities [Member]		Mar. 31, 2012 Accumulated Net Unrealized Gain (Loss) on Available for Sale Securities [Member]		Mar. 31, 2013 Accumulated Unrealized Gain on AFS Securities Transferred to Investment Securities [Member]		Mar. 31, 2012 Accumulated Unrealized Gain on AFS Securities Transferred to Investment Securities [Member]		Mar. 31, 2013 Accumulated Defined Benefit Plans Adjustment [Member]		Mar. 31, 2012 Accumulated Defined Benefit Plans Adjustment [Member]		Mar. 31, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]		Mar. 31, 2012 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]		Apr. 30, 2013 Dividend Declared [Member]
Dividends declared (in dollars per share)	$ 0.38		$ 0.33																		$ 0.38
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance, Beginning of Period	$ 149,920		$ 128,979		$ 155,553		$ 135,740		$ 3,078		$ 6,673		$ (8,296)		$ (12,742)		$ (415)		$ (692)
Net change in unrealized gain (loss)	(21,359)		55,435		(21,359)		55,726		0		0		0		(291)		0		0
Reclassification Adjustments Included in Earnings [Abstract]
Interest revenue, Investment securities, Taxable securities	(1,148)		(1,788)		0		0		(1,148)		(1,788)		0		0		0		0
Interest Expense, Subordinated Debt	52		52		0		0		0		0		0		0		52		52
Net impairment losses recognized in earnings	247		3,722		247		3,722		0		0		0		0		0		0
Gain on available for sale securities, net	(4,855)		(4,331)		(4,855)		(4,331)		0		0		0		0		0		0
Other comprehensive income (loss), before income taxes	(27,063)		53,090		(25,967)		55,117		(1,148)		(1,788)		0		(291)		52		52
Income tax expense (benefit)	10,526	[1]	(20,651)	[1]	10,100	[1]	(21,441)	[1]	446	[1]	697	[1]	0	[1]	113	[1]	(20)	[1]	(20)	[1]
Other comprehensive income (loss), net of income taxes	(16,537)		32,439		(15,867)		33,676		(702)		(1,091)		0		(178)		32		32
Balance, End of Period	$ 133,383		$ 161,418		$ 139,686		$ 169,416		$ 2,376		$ 5,582		$ (8,296)		$ (12,920)		$ (383)		$ (660)

[1] Calculated using a 39% effective tax rate.