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Statutory Accounting and Regulatory Requirements - Insurance Subsidiaries (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Insurance [Abstract] |  |  |
Capital and surplus | $ 377,742 us-gaap_StatutoryAccountingPracticesStatutoryCapitalAndSurplusBalance | $ 354,293 us-gaap_StatutoryAccountingPracticesStatutoryCapitalAndSurplusBalance | $ 323,932 us-gaap_StatutoryAccountingPracticesStatutoryCapitalAndSurplusBalance
Net income | 50,205 us-gaap_StatutoryAccountingPracticesStatutoryNetIncomeAmount | 44,751 us-gaap_StatutoryAccountingPracticesStatutoryNetIncomeAmount | 31,059 us-gaap_StatutoryAccountingPracticesStatutoryNetIncomeAmount
Realized investment gains (losses) | $ 693 amsf_StatutoryAccountingPracticesStatutoryRealizedInvestmentGainsLosses | $ (1,214)amsf_StatutoryAccountingPracticesStatutoryRealizedInvestmentGainsLosses | $ 2,958 amsf_StatutoryAccountingPracticesStatutoryRealizedInvestmentGainsLosses

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- Definition Statutory Accounting Practices Statutory Realized Investment Gains Losses + References No definition available. + Details
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- Details
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- Definition The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.23(c)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 24 -Subparagraph c -Article 7 + Details
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- Definition Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.23(c)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 24 -Subparagraph c -Article 7 + Details
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