XML 31 R28.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Investments - Gross Unrealized Gains and Losses and Cost or Amortized Cost and Fair Value of Investments Classified as Available-for-sale (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
--- | --- | ---
Investment [Line Items] |  |
Cost or Amortized Cost | $ 229,184 | $ 151,514
Gross Unrealized Gains | 3,036 | 6,101
Gross Unrealized Losses | (6,988) | (1,710)
Fair Value | 225,232 | 155,905
States and political subdivisions [Member] |  |
Investment [Line Items] |  |
Cost or Amortized Cost | 133,239 | 93,362
Gross Unrealized Gains | 1,694 | 5,022
Gross Unrealized Losses | (4,375) | (142)
Fair Value | 130,558 | 98,242
Corporate bonds [Member] |  |
Investment [Line Items] |  |
Cost or Amortized Cost | 63,876 | 39,211
Gross Unrealized Gains | 471 | 623
Gross Unrealized Losses | (245) | (24)
Fair Value | 64,102 | 39,810
U.S. agency-based mortgage-backed securities [Member] |  |
Investment [Line Items] |  |
Cost or Amortized Cost | 10,082 | 11,941
Gross Unrealized Gains |  | 5
Gross Unrealized Losses | (2,041) | (859)
Fair Value | 8,041 | 11,087
Total fixed maturity [Member] |  |
Investment [Line Items] |  |
Cost or Amortized Cost | 207,197 | 144,514
Gross Unrealized Gains | 2,165 | 5,650
Gross Unrealized Losses | (6,661) | (1,025)
Fair Value | 202,701 | 149,139
Other Investments [Member] |  |
Investment [Line Items] |  |
Cost or Amortized Cost | 10,000 |
Gross Unrealized Gains | 271 |
Gross Unrealized Losses |  |
Fair Value | 10,271 |
Equity Securities [Member] |  |
Investment [Line Items] |  |
Cost or Amortized Cost | 11,987 | 7,000
Gross Unrealized Gains | 600 | 451
Gross Unrealized Losses | (327) | (685)
Fair Value | $ 12,260 | $ 6,766

X
- Definition Amount of accumulated pre-tax unrealized gain before deducting pre-tax unrealized losses on investments in available-for-sale securities impacting investments. + References No definition available. + Details
Name: | amsf_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated pre-tax unrealized loss before deducting pre-tax unrealized gain on investments in available-for-sale securities impacting investments. + References No definition available. + Details
Name: | amsf_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | invest_InvestmentLineItems
Namespace Prefix: | invest_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
Name: | us-gaap_AvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant