Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets:
Fixed income securities, at fair value (amortized cost of $6,121,910 in 2014 and $5,927,254 in 2013)	$ 6,168,689	$ 5,885,316
Fixed income securities pledged as collateral, at fair value (amortized cost of $125,090 in 2014 and $126,196 in 2013)	125,123	126,223
Short-term investments, at fair value (amortized cost of $215,103 in 2014 and $271,118 in 2013)	215,103	271,119
Other investments, at fair value	240,530	241,069
Total investments	6,749,445	6,523,727
Cash	31,700	77,370
Receivable for securities	36,447	14,450
Investment income due and accrued	34,641	37,663
Premium receivables	1,418,114	1,453,021
Reinsurance recoverable on paid and unpaid losses	111,442	121,249
Deferred ceded premium	142,280	145,529
Subrogation recoverable	512,235	498,478
Loans	6,250	6,179
Derivative assets	81,911	77,711
Insurance intangible asset	1,570,070	1,597,965
Goodwill	514,511	514,511
Other assets	72,865	35,927
Variable interest entity assets:
Fixed income securities, at fair value	6,168,689	5,885,316
Investment income due and accrued	34,641	37,663
Other assets	72,865	35,927
Total assets	27,114,248	27,092,477
Liabilities:
Unearned premiums	2,167,764	2,255,680
Losses and loss expense reserve	5,826,168	5,968,712
Ceded premiums payable	69,892	70,962
Obligations under investment agreements	359,993	359,070
Deferred taxes	2,202	2,199
Current taxes	3,761	738
Long-term debt	972,147	963,178
Accrued interest payable	317,052	294,817
Derivative liabilities	300,840	253,898
Other liabilities	58,819	67,377
Payable for securities purchased	79,697	4,654
Variable interest entity liabilities:
Accrued interest payable	317,052	294,817
Long-term debt, at fair value	972,147	963,178
Derivative liabilities	300,840	253,898
Other liabilities	58,819	67,377
Total liabilities	25,885,437	26,114,055
Stockholders’ equity:
Preferred stock, par value $0.01 per share; authorized shares—20,000,000; issued and outstanding shares—none	0	0
Common stock, par value $0.01 per share; authorized shares—130,000,000; issued and outstanding shares—45,003,512 at March 31, 2014 and 45,003,461 at December 31, 2013	450	450
Additional paid-in capital	187,210	185,672
Accumulated other comprehensive income	104,417	11,661
Accumulated earnings	661,161	505,219
Common stock held in treasury at cost, 937 shares at March 31, 2014 and December 31, 2013	(19)	(19)
Total Ambac Financial Group, Inc. stockholders’ equity	953,219	702,983
Noncontrolling interest	275,592	275,439
Total stockholders’ equity	1,228,811	978,422
Total liabilities and stockholders’ equity	27,114,248	27,092,477
Variable Interest Entity [Member]
Assets:
Fixed income securities, at fair value (amortized cost of $6,121,910 in 2014 and $5,927,254 in 2013)	2,546,762	2,475,182
Investment income due and accrued	4,247	1,365
Other assets	3,324	19,617
Variable interest entity assets:
Fixed income securities, at fair value	2,546,762	2,475,182
Restricted cash	8,552	17,498
Investment income due and accrued	4,247	1,365
Loans, at fair value	13,269,452	13,398,895
Intangible assets	0	76,140
Other assets	3,324	19,617
Liabilities:
Long-term debt	13,878,577	14,091,753
Accrued interest payable	3,569	722
Derivative liabilities	1,844,690	1,772,306
Other liabilities	266	7,989
Variable interest entity liabilities:
Accrued interest payable	3,569	722
Long-term debt, at fair value	13,878,577	14,091,753
Derivative liabilities	1,844,690	1,772,306
Other liabilities	$ 266	$ 7,989