XML 21 R55.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Investments - Investment Securities Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2013 | Dec. 31, 2012
--- | --- | ---
Investment [Line Items] |  |
Fair Value of Investments with Unrealized Losses, Less Than 12 months | $ 207,092 | $ 50,561
Gross Unrealized Loss, Less Than 12 Months | 7,379 | 1,828
Fair Value of Investments with Unrealized Losses, 12 Months or Greater | 9,752 | 2,345
Gross Unrealized Losses | 1,338 | 299
Gross Unrealized Losses, 12 Months or Greater | 2,994 | 181
Fair Value of Investments with Unrealized Losses, Total | 216,844 | 52,906
Gross Unrealized Losses, Total | 10,373 | 2,009
Available-for-sale securities [Member] |  |
Investment [Line Items] |  |
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 138,107 | 27,797
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 6,191 | 1,710
Fair Value of Investments with Unrealized Losses, 12 Months or Greater | 7,525 |
Gross Unrealized Losses, 12 Months or Greater | 2,844 |
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 145,632 | 27,797
Available-for Sale, Gross Unrealized Losses, Total | 9,035 | 1,710
Available-for-sale securities [Member] | Corporate bonds [Member] |  |
Investment [Line Items] |  |
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 29,691 | 6,411
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 361 | 24
Fair Value of Investments with Unrealized Losses, 12 Months or Greater |  |
Gross Unrealized Losses, 12 Months or Greater |  |
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 29,691 | 6,411
Available-for Sale, Gross Unrealized Losses, Total | 361 | 24
Available-for-sale securities [Member] | States and political subdivisions [Member] |  |
Investment [Line Items] |  |
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 101,908 | 6,281
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 4,798 | 142
Fair Value of Investments with Unrealized Losses, 12 Months or Greater | 1,753 |
Gross Unrealized Losses, 12 Months or Greater | 342 |
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 103,661 | 6,281
Available-for Sale, Gross Unrealized Losses, Total | 5,140 | 142
Available-for-sale securities [Member] | U.S. agency-based mortgage-backed securities [Member] |  |
Investment [Line Items] |  |
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 1,303 | 10,919
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 465 | 859
Fair Value of Investments with Unrealized Losses, 12 Months or Greater | 5,772 |
Gross Unrealized Losses, 12 Months or Greater | 2,502 |
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 7,075 | 10,919
Available-for Sale, Gross Unrealized Losses, Total | 2,967 | 859
Available-for-sale securities [Member] | Equity securities [Member] |  |
Investment [Line Items] |  |
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 5,205 | 4,186
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 567 | 685
Fair Value of Investments with Unrealized Losses, 12 Months or Greater |  |
Gross Unrealized Losses, 12 Months or Greater |  |
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 5,205 | 4,186
Available-for Sale, Gross Unrealized Losses, Total | 567 | 685
Held-to-maturity securities [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 68,985 | 22,764
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss | 1,188 | 118
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 2,227 | 2,345
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss | 150 | 181
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 71,212 | 25,109
Gross Unrealized Losses | 1,338 | 299
Held-to-maturity securities [Member] | Corporate bonds [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 14,090 | 10,734
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss | 41 | 12
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  |
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 14,090 | 10,734
Gross Unrealized Losses | 41 | 12
Held-to-maturity securities [Member] | States and political subdivisions [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 54,895 | 11,913
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss | 1,147 | 106
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 311 |
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss | 6 |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 55,206 | 11,913
Gross Unrealized Losses | 1,153 | 106
Held-to-maturity securities [Member] | U.S. agency-based mortgage-backed securities [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | 117
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 68
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss |  | 5
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value |  | 185
Gross Unrealized Losses |  | 5
Held-to-maturity securities [Member] | Asset-backed securities [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  |
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,916 | 2,277
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss | 144 | 176
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 1,916 | 2,277
Gross Unrealized Losses | $ 144 | $ 176

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

X
- Definition Amount of accumulated pre-tax unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months impacting investments. + References No definition available. + Details
Name: | amsf_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsAggregateLossesAccumulatedInInvestments
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Continuous Unrealized Loss Position Greater Than Twelve Months Aggregate Losses + References No definition available. + Details
Name: | amsf_ContinuousUnrealizedLossPositionGreaterThanTwelveMonthsAggregateLosses
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Continuous Unrealized Loss Position Greater Than Twelve Months Fair Value + References No definition available. + Details
Name: | amsf_ContinuousUnrealizedLossPositionGreaterThanTwelveMonthsFairValue
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses + References No definition available. + Details
Name: | amsf_ContinuousUnrealizedLossPositionLessThanTwelveMonthsAggregateLosses
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Continuous Unrealized Loss Position Less Than Twelve Months Fair Value + References No definition available. + Details
Name: | amsf_ContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the excess of amortized cost basis over fair value of securities in a loss position and which are categorized as held-to-maturity. + References No definition available. + Details
Name: | amsf_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for those securities which are categorized as held-to-maturity. + References No definition available. + Details
Name: | amsf_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsAccumulatedLoss
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of accumulated pre-tax unrealized loss on investments in held-to-maturity securities that have been in a loss position for twelve months or longer. + References No definition available. + Details
Name: | amsf_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerAccumulatedLoss
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Securities continuous unrealized loss position aggregate losses. + References No definition available. + Details
Name: | amsf_SecuritiesContinuousUnrealizedLossPositionAggregateLosses
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Securities continuous unrealized loss position fair value. + References No definition available. + Details
Name: | amsf_SecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | amsf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities categorized as held-to-maturity which are in an unrealized loss position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities categorized as held-to-maturity securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant