Shareholders' Equity (Details) (USD $) In Thousands, except Per Share data	1 Months Ended	3 Months Ended				6 Months Ended
	Jul. 26, 2011	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Shareholders' Equity [Abstract]
Dividends declared (in dollars per share)	$ 0.275	$ 0.275		$ 0.25		$ 0.525		$ 0.49
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance at Beginning of Period	$ 146,255					$ 107,839		$ (10,740)
Net change in unrealized gains (losses) on securities						64,018		207,888
Unrealized loss on newly identified other-than-temporary securities								0
Credit losses recognized in earnings						9,349		6,871
Transfer from non-credit related unrealized losses on OTTI securities to unrealized gain on available for sale securities						0
Tax benefit (expense) on unrealized gains (losses)						(28,710)		(83,045)
Reclassification adjustment for (gains) losses realized and included in net income						(10,214)		(12,409)
Reclassification adjustment for tax expense (benefit)on realized gains (losses)						3,973		4,833
Unrealized gains on employee benefit plans						0		373
Balance at End of Period		146,255		113,771		146,255		113,771
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance at Beginning of Period						157,770		59,772
Net change in unrealized gains (losses) on securities						73,466		195,882
Unrealized loss on newly identified other-than-temporary securities								20,667
Credit losses recognized in earnings						0		0
Transfer from non-credit related unrealized losses on OTTI securities to unrealized gain on available for sale securities						180
Tax benefit (expense) on unrealized gains (losses)						(29,372)		(83,845)
Reclassification adjustment for (gains) losses realized and included in net income						(10,370)		(12,545)
Reclassification adjustment for tax expense (benefit)on realized gains (losses)						4,034		4,886
Unrealized gains on employee benefit plans						0		0
Balance at End of Period		195,708		184,817		195,708		184,817
Accumulated Other-than-Temporary Impairment [Member]
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance at Beginning of Period						(35,276)	[1]	(53,000)	[1]
Net change in unrealized gains (losses) on securities						(9,448)	[1]	12,006	[1]
Unrealized loss on newly identified other-than-temporary securities								(20,667)	[1]
Credit losses recognized in earnings						9,349	[1]	6,871	[1]
Transfer from non-credit related unrealized losses on OTTI securities to unrealized gain on available for sale securities						(180)	[1]
Tax benefit (expense) on unrealized gains (losses)						662	[1]	945	[1]
Reclassification adjustment for (gains) losses realized and included in net income						0	[1]	0	[1]
Reclassification adjustment for tax expense (benefit)on realized gains (losses)						0	[1]	0	[1]
Unrealized gains on employee benefit plans						0	[1]	0	[1]
Balance at End of Period		(34,893)	[1]	(53,845)	[1]	(34,893)	[1]	(53,845)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance at Beginning of Period						(878)		(1,039)
Net change in unrealized gains (losses) on securities						0		0
Unrealized loss on newly identified other-than-temporary securities								0
Credit losses recognized in earnings						0		0
Transfer from non-credit related unrealized losses on OTTI securities to unrealized gain on available for sale securities						0
Tax benefit (expense) on unrealized gains (losses)						0		0
Reclassification adjustment for (gains) losses realized and included in net income						156		136
Reclassification adjustment for tax expense (benefit)on realized gains (losses)						(61)		(53)
Unrealized gains on employee benefit plans						0		0
Balance at End of Period		(783)		(956)		(783)		(956)
Accumulated Defined Benefit Plans Adjustment [Member]
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance at Beginning of Period						(13,777)		(16,473)
Net change in unrealized gains (losses) on securities						0		0
Unrealized loss on newly identified other-than-temporary securities								0
Credit losses recognized in earnings						0		0
Transfer from non-credit related unrealized losses on OTTI securities to unrealized gain on available for sale securities						0
Tax benefit (expense) on unrealized gains (losses)						0		(145)
Reclassification adjustment for (gains) losses realized and included in net income						0		0
Reclassification adjustment for tax expense (benefit)on realized gains (losses)						0		0
Unrealized gains on employee benefit plans						0		373
Balance at End of Period		$ (13,777)		$ (16,245)		$ (13,777)		$ (16,245)

[1] Represents changes in unrealized losses recognized in AOCI on available for sale securities for which an other-than-temporary impairment ("OTTI") was recorded in earnings.