Special Purpose Entities, Including Variable Interest Entities (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended				6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Entity	Jun. 30, 2011	Dec. 31, 2011	Mar. 31, 2011	Jun. 30, 2012 Asset Backed Securities and Utility Obligations [Member]	Jun. 30, 2011 Asset Backed Securities and Utility Obligations [Member]	Jun. 30, 2012 Asset Backed Securities and Utility Obligations [Member]	Jun. 30, 2012 Sponsored Variable Interest Entities [Member] Transactions	Dec. 31, 2011 Sponsored Variable Interest Entities [Member]	Jun. 30, 2012 Financial Guarantee [Member]	Jun. 30, 2011 Financial Guarantee [Member]	Jun. 30, 2012 Financial Guarantee [Member]	Jun. 30, 2011 Financial Guarantee [Member]	Jun. 30, 2012 Variable Interest Entity [Member]	Dec. 31, 2011 Variable Interest Entity [Member]	Jun. 30, 2012 Consolidated Entities [Member] Entity	Dec. 31, 2011 Consolidated Entities [Member] Entity	Jun. 30, 2012 Unconsolidated Variable Interest Entities [Member]	Jun. 30, 2011 Unconsolidated Variable Interest Entities [Member]	Jun. 30, 2012 Unconsolidated Variable Interest Entities [Member]	Jun. 30, 2011 Unconsolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Debt outstanding to third parties under this secured borrowing transaction																$ 24,964	$ 35,600
Securities fair value	193,346		193,346		172,880											193,346	172,880
Number of individual transactions with special purpose entities										15
Number of transactions were outstanding with special purpose entities										5
Total principal amount of debt outstanding										574,509	578,562
Average rating of assets held by sponsored special purpose entities			no longer than 90 days						BBB+
Weighted average life									8 years 1 month 6 days
Value of assets sold to special purpose entities
Earned fees for providing other services under its financial guarantee policies												11	12	22	23
Number of consolidated entities																		18	19
Income (loss) on variable interest entities																				0	0	0	0
Special Purpose Entities, Including Variable Interest Entities (Textual) [Abstract]
Number of special purpose entities sponsored by Ambac			2
Fair value of special purpose entities	15,792		15,792		16,779
Change in fair value of special purpose entities	(231)	(554)	(987)	542
Earned premiums for issuing the financial guarantee policies on the assets, MTNs and derivative contracts	110	191	255	427
Claims paid to entities under its financial guarantee policies
Amount paid under derivative contracts	0	0
Amount received under derivative contracts	3,886	4,206	3,747	4,075
Consolidated VIE assets	16,620,359		16,620,359		16,543,207
VIE - Derivative liabilities, Fair value	16,444,608		16,444,608		16,379,386
Intangible assets recorded at fair value						326,342
Accumulated amortization on the intangible assets		8,162		8,162
Amortization expense for intangible assets		$ 8,162		$ 8,162
Weighted average amortization period			28 years