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Investments - Summary of Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended | 8 Months Ended | 4 Months Ended | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2013 Successor Ambac [Member] | Apr. 30, 2013 Predecessor Ambac [Member] | Dec. 31, 2012 Predecessor Ambac [Member]
Investment [Line Items] |  |  |  |
Fixed income securities |  | $ 147,014 | $ 118,097 | $ 386,385
Short-term investments |  | 1,528 | 677 | 1,405
Loans |  | 306 | 146 | 714
Investment expense |  | (5,982) | (2,549) | (5,602)
Securities available-for-sale and short-term |  | 142,866 | 116,371 | 382,902
Other investments | 0 | 3,580 | 369 |
Total net investment income |  | $ 146,446 | $ 116,740 | $ 382,902

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- Definition Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.2) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 2 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24721-111560 + Details
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