Shareholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended										0 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Jun. 30, 2011 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Jun. 30, 2012 Accumulated Unrealized Gain on AFS Securities Transferred to Investment Securities [Member]	Jun. 30, 2011 Accumulated Unrealized Gain on AFS Securities Transferred to Investment Securities [Member]	Jun. 30, 2012 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	Jun. 30, 2011 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	Jun. 30, 2012 Accumulated Defined Benefit Plans Adjustment [Member]	Jun. 30, 2011 Accumulated Defined Benefit Plans Adjustment [Member]	Jul. 31, 2012 Dividend Declared [Member]
Dividends declared (in dollars per share)	$ 0.38	$ 0.275	$ 0.71	$ 0.525									$ 0.38
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance at Beginning of Period			$ 128,979	$ 107,839	$ 135,740	$ 122,494	$ 6,673	$ 0	$ (692)	$ (878)	$ (12,742)	$ (13,777)
Net change in unrealized gains (losses) on securities	(15,401)	62,502	40,034	63,943	40,325	63,944	0	0	0	0	(291)	(1)
Credit losses recognized in earnings			4,580	9,423	4,580	9,423	0	0	0	0	0	0
Amortization of unrealized gain on investment securities transferred from AFS			(3,421)		0		(3,421)		0		0
Reclassification adjustment for (gains) losses realized and included in net income	(20,202)	(5,395)	(24,481)	(10,214)	(24,812)	(10,370)	0	0	331	156	0	0
Other Comprehensive Income (Loss), Tax	14,150	(23,989)	(6,501)	(24,736)	(7,816)	(24,676)	1,331	0	(129)	(60)	113	0
Balance at End of Period	$ 139,190	$ 146,255	$ 139,190	$ 146,255	$ 148,017	$ 160,815	$ 4,583	$ 0	$ (490)	$ (782)	$ (12,920)	$ (13,778)