XML 28 R35.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2014 | Dec. 31, 2013
--- | --- | ---
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | $ 332,104 | $ 257,770
Equity securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 3,598 | 9,302
Other investments [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 11,228 | 10,591
Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 332,104 | 257,770
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 317,278 | 237,877
Fair Value, Measurements, Recurring [Member] | Other investments [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 11,228 | 10,591
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Equity securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 3,598 | 9,302
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 156,789 | 150,375
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 152,670 | 80,428
Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 7,819 | 7,074
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 3,598 | 9,302
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Equity securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 3,598 | 9,302
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 317,278 | 237,877
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 317,278 | 237,877
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 156,789 | 150,375
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 152,670 | 80,428
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 7,819 | 7,074
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 11,228 | 10,591
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other investments [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | $ 11,228 | $ 10,591

X
- Details
Name: | amsf_FairValueMeasurementsDisclosureLineItems
Namespace Prefix: | amsf_
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