Long-Term Debt and Credit Facilities (Details) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Debt
Principal	$ 1,354,900,000	$ 1,371,800,000
Carrying Value	1,041,653,000	1,052,936,000
AGUS (Consolidated)
Debt
Principal	522,500,000	522,500,000
Carrying Value	519,200,000	518,400,000
AGUS (Consolidated) | 7.0% Senior Notes
Debt
Principal	200,000,000	200,000,000
Carrying Value	197,600,000	197,600,000
Interest rate of debt (as a percent)	7.00%	7.00%
AGUS (Consolidated) | 8.50% Senior Notes
Debt
Principal	172,500,000	172,500,000
Carrying Value	171,800,000	171,000,000
Interest rate of debt (as a percent)	8.50%	8.50%
AGUS (Consolidated) | Series A Enhanced Junior Subordinated Debentures
Debt
Principal	150,000,000	150,000,000
Carrying Value	149,800,000	149,800,000
AGMH (Consolidated)
Debt
Principal	730,000,000	730,000,000
Carrying Value	413,200,000	407,500,000
AGMH (Consolidated) | 6 7/8% QUIBS
Debt
Principal	100,000,000	100,000,000
Carrying Value	67,300,000	67,000,000
Interest rate of debt (as a percent)	6.875%	6.875%
AGMH (Consolidated) | 6.25% Notes
Debt
Principal	230,000,000	230,000,000
Carrying Value	135,700,000	135,000,000
Interest rate of debt (as a percent)	6.25%	6.25%
AGMH (Consolidated) | 5.60% Notes
Debt
Principal	100,000,000	100,000,000
Carrying Value	53,400,000	53,000,000
Interest rate of debt (as a percent)	5.60%	5.60%
AGMH (Consolidated) | Junior Subordinated Debentures
Debt
Principal	300,000,000	300,000,000
Carrying Value	156,800,000	152,500,000
AGM Consolidated [Member]
Debt
Principal	102,400,000	119,300,000
Carrying Value	109,300,000	127,000,000
AGM Consolidated [Member] | Notes Payable.
Debt
Principal	102,400,000	119,300,000
Carrying Value	$ 109,300,000	$ 127,000,000