Investments - Below investment grade securities (Details) (USD $)						9 Months Ended
Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Private label residential mortgage backed securities	Dec. 31, 2011 Private label residential mortgage backed securities	Sep. 30, 2012 Below investment grade Private label residential mortgage backed securities	Sep. 30, 2012 PHHAM Below investment grade Private label residential mortgage backed securities	Sep. 30, 2012 CWALT ONE Below investment grade Private label residential mortgage backed securities	Sep. 30, 2012 CWALT TWO Below investment grade Private label residential mortgage backed securities	Sep. 30, 2012 FHAMS Below investment grade Private label residential mortgage backed securities	Sep. 30, 2012 BAALT Below investment grade Private label residential mortgage backed securities	Sep. 30, 2012 ABFS Below investment grade Private label residential mortgage backed securities	Sep. 30, 2012 CONHE Below investment grade Private label residential mortgage backed securities
Schedule of Available-for-sale Securities
Debt Securities, Amortized Cost			$ 6,728,000	$ 8,408,000	$ 5,177,000	$ 1,984,000	$ 690,000	$ 310,000	$ 1,799,000	$ 93,000	$ 255,000	$ 46,000
Available-for-sale Securities	364,808,000	328,413,000			4,964,000	1,841,000	648,000	264,000	1,873,000	60,000	208,000	70,000
Unrealized Gain (Loss)	$ 13,771,000	$ 7,008,000	$ 50,000		$ (213,000)	$ (143,000)	$ (42,000)	$ (46,000)	$ 74,000	$ (33,000)	$ (47,000)	$ 24,000
12 Month Historical Prepayment Rates %						11.39%	12.77%	12.37%	12.46%	11.09%	8.28%	13.00%
Projected Default Rates %						21.60%	26.80%	28.70%	17.80%	11.70%	8.85%	6.12%
Projected Severity Rates %						51.00%	58.20%	58.50%	47.80%	51.00%	65.00%	67.33%
Original Purchase Price %						97.25%	100.73%	101.38%	95.00%	97.24%	97.46%	86.39%
Current Credit Enhancement %						0.00%	3.23%	(0.58%)	(0.43%)	3.14%	0.00%	0.00%

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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