Other-Than-Temporary Impairment (Rollforward) (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 328,937,000		$ 312,891,000	$ 322,589,000		$ 317,344,000
Credit losses for which OTTI was not previously recognized	0		0	74,000		659,000
Additional OTTI credit losses for which an OTTI charge was previously recognized	186,000	[1]	6,173,000	10,950,000	[1]	36,870,000
Securities sold and matured during the period	265,000		0	265,000		(30,687,000)
Increases in cash flows expected to be collected, recognized over the remaining life of the securities	(2,209,000)	[2]	(2,110,000)	(6,699,000)	[2]	7,232,000
Ending balance	$ 327,179,000		$ 316,954,000	$ 327,179,000		$ 316,954,000

[1] For the three months ended September 30, 2012 and 2011, OTTI "previously recognized" represents securities that were impaired prior to July 1, 2012 and 2011. For the nine months ended September 30, 2012 and 2011, OTTI "previously recognized" represents securities that were impaired prior to January 1, 2012 and 2011

[2] This activity represents the increase in cash flows recognized in interest income during the period.