Shareholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended																				1 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013 Accumulated Net Unrealized Gain (Loss) on Available for Sale Securities [Member]		Jun. 30, 2012 Accumulated Net Unrealized Gain (Loss) on Available for Sale Securities [Member]		Jun. 30, 2013 Accumulated Unrealized Gain on Investment Securities Transferred from AFS [Member]		Jun. 30, 2012 Accumulated Unrealized Gain on Investment Securities Transferred from AFS [Member]		Jun. 30, 2013 Accumulated Unrealized Gain (Loss) on Employee Benefit Plans [Member]		Jun. 30, 2012 Accumulated Unrealized Gain (Loss) on Employee Benefit Plans [Member]		Jun. 30, 2013 Accumulated Loss on Effective Cash Flow Hedges [Member]		Jun. 30, 2012 Accumulated Loss on Effective Cash Flow Hedges [Member]		Apr. 30, 2013 Dividend Declared [Member]
Dividends declared (in dollars per share)	$ 0.38	$ 0.38	$ 0.76		$ 0.71																		$ 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)	(183,186)	(15,401)	(204,545)		40,034		(204,545)		40,325		0		0		0		(291)		0		0
Reclassification Adjustments Included in Earnings [Abstract]
Interest revenue, Investment securities, Taxable securities	(873)	(1,633)	(2,021)		(3,421)		0		0		(2,021)		(3,421)		0		0		0		0
Interest Expense, Subordinated debentures	72	279	124		331		0		0		0		0		0		0		124		331
Net impairment losses recognized in earnings	552	858	799		4,580		799		4,580		0		0		0		0		0		0
Gain on available for sale securities, net	(3,753)	(20,481)	(8,608)		(24,812)		(8,608)		(24,812)		0		0		0		0		0		0
Other comprehensive income (loss), before income taxes	(187,188)	(36,378)	(214,251)		16,712		(212,354)		20,093		(2,021)		(3,421)		0		(291)		124		331
Income tax benefit (expense)	72,819	14,150	83,345	[1]	(6,501)	[1]	82,605	[1]	(7,816)	[1]	788	[1]	1,331	[1]	0	[1]	113	[1]	(48)	[1]	(129)	[1]
Other comprehensive income (loss), net of income taxes	(114,369)	(22,228)	(130,906)		10,211		(129,749)		12,277		(1,233)		(2,090)		0		(178)		76		202
Balance, End of Period	$ 19,014	$ 139,190	$ 19,014		$ 139,190		$ 25,804		$ 148,017		$ 1,845		$ 4,583		$ (8,296)		$ (12,920)		$ (339)		$ (490)

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