Derivatives (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Credit default swap, notional value	$ 33,100,000		$ 33,100,000
Credit default swap, exposure to loss, maximum per reference entity	20,000,000
Credit default swap, fair value	18,300,000		29,300,000
Gain on derivative instrument recognized in earnings	$ 11,100,000	$ 1,700,000
Weighted average expected default rate	5.00%		9.00%
Weighted average expected recovery rate	39.00%		39.00%
Minimum [Member]
Derivatives, Fair Value [Line Items]
Expected default rate	1.00%		2.00%
Credit derivative expected recovery rate	19.00%		19.00%
Maximum [Member]
Derivatives, Fair Value [Line Items]
Expected default rate	37.00%		37.00%
Credit derivative expected recovery rate	52.00%		52.00%