XML 75 R56.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Investments (Details 5) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2012 | Sep. 30, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2011 | Sep. 30, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Major categories of the Company's net investment income |  |  |  |  |  |  |  |  |  |  |
Total gross investment income |  |  |  |  |  |  |  |  | $ 28,102 | $ 27,540 | $ 27,461
Investment expenses |  |  |  |  |  |  |  |  | (1,084) | (1,200) | (1,219)
Net investment income | 6,698 | 6,801 | 6,605 | 6,914 | 6,702 | 6,495 | 6,597 | 6,546 | 27,018 | 26,340 | 26,242
Fixed Maturity Securities Available for Sale [Member] |  |  |  |  |  |  |  |  |  |  |
Major categories of the Company's net investment income |  |  |  |  |  |  |  |  |  |  |
Total gross investment income |  |  |  |  |  |  |  |  | 27,167 | 26,769 | 26,571
Short-term Investments [Member] |  |  |  |  |  |  |  |  |  |  |
Major categories of the Company's net investment income |  |  |  |  |  |  |  |  |  |  |
Total gross investment income |  |  |  |  |  |  |  |  | 489 | 590 | 819
Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Major categories of the Company's net investment income |  |  |  |  |  |  |  |  |  |  |
Total gross investment income |  |  |  |  |  |  |  |  | $ 446 | $ 181 | $ 71

X
- Definition Gross investment income. + References No definition available. + Details
Name: | amsf_GrossInvestmentIncome
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Total expenses related to the generation of investment income in debt and equity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.9) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 + Details
Name: | us-gaap_InvestmentIncomeInvestmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The income earned from investments in securities and property, equipment and other capital assets. It includes rent from property and equipment, dividends from shares in corporations, and interest from bonds, loans, mortgages, derivatives, commercial paper, bank accounts, certificates of deposits, treasuries, and other financial securities. It does not include realized gains and losses on investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.2) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 2 -Article 7 + Details
Name: | us-gaap_NetInvestmentIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_NetInvestmentIncomeAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration