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Investment Securities AFS and HTM Gross Unrealized Losses (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Unrealized losses and fair value of available for sale securities , by investment category and time length    
Unrealized losses on available for sale securities, less than 12 months $ (910)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss $ (3,189)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
Unrealized losses on available for sale securities, 12 months or more (25,436)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss (53,343)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
Total unrealized losses on available for sale securities (26,346)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss (56,532)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
Fair value of unrealized losses on available for sale securities, less than 12 months 305,776us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue 669,839us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Fair value of unrealized losses on available for sale securities, 12 months or more 1,516,536us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue 1,719,118us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Total fair value of unrealized losses on available for sale securities 1,822,312us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue 2,388,957us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]    
Unrealized losses on held to maturity securities, less than 12 months (568)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss (216)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
Unrealized losses on held to maturity securities, 12 months or more (264)asb_Heldtomaturitysecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss (616)asb_Heldtomaturitysecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
Total unrealized losses on held to maturity securities (832)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionaccumulatedloss (832)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionaccumulatedloss
Fair value of unrealized losses on held to maturity securities, less than 12 months 73,163us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue 31,924us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Fair value of unrealized losses on held to maturity securities, 12 months or more 9,552us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue 38,915us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Total fair value of unrealized losses on held to maturity securities 82,715us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue 70,839us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
US Treasury Securities [Member]    
Unrealized losses and fair value of available for sale securities , by investment category and time length    
Unrealized losses on available for sale securities, less than 12 months   (1)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Unrealized losses on available for sale securities, 12 months or more   0asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Total unrealized losses on available for sale securities   (1)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Fair value of unrealized losses on available for sale securities, less than 12 months   998us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Fair value of unrealized losses on available for sale securities, 12 months or more   0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Total fair value of unrealized losses on available for sale securities   998us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Number of available for sale securities in a continuous unrealized loss position less than twelve months   1us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Number of available for sale securities in a continuous unrealized loss position for twelve months or more   0us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Obligations of state and political subdivisions (municipal securities) [Member]    
Unrealized losses and fair value of available for sale securities , by investment category and time length    
Unrealized losses on available for sale securities, less than 12 months (1)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
(9)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Unrealized losses on available for sale securities, 12 months or more (3)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
(20)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Total unrealized losses on available for sale securities (4)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
(29)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair value of unrealized losses on available for sale securities, less than 12 months 629us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
3,374us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair value of unrealized losses on available for sale securities, 12 months or more 186us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
2,133us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Total fair value of unrealized losses on available for sale securities 815us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
5,507us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Number of available for sale securities in a continuous unrealized loss position less than twelve months 2us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
6us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Number of available for sale securities in a continuous unrealized loss position for twelve months or more 1us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
6us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]    
Unrealized losses on held to maturity securities, less than 12 months (568)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
(216)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Unrealized losses on held to maturity securities, 12 months or more (264)asb_Heldtomaturitysecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
(616)asb_Heldtomaturitysecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Total unrealized losses on held to maturity securities (832)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
(832)asb_Heldtomaturitysecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair value of unrealized losses on held to maturity securities, less than 12 months 73,163us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
31,924us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair value of unrealized losses on held to maturity securities, 12 months or more 9,552us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
38,915us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Total fair value of unrealized losses on held to maturity securities 82,715us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
70,839us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Obligations of state and political subdivisions (municipal securities) [Member] | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]    
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]    
Number of held to maturity securities in a continuous unrealized loss position 163us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ asb_LengthoftimeheldtomaturitysecuritiesareincontinuousunrealizedlosspositionAxis
= asb_HeldtomaturitysecuritiesinunrealizedlosspositionsqualitativedisclosurenumberofpositionslessthanoneyearMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
74us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ asb_LengthoftimeheldtomaturitysecuritiesareincontinuousunrealizedlosspositionAxis
= asb_HeldtomaturitysecuritiesinunrealizedlosspositionsqualitativedisclosurenumberofpositionslessthanoneyearMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Obligations of state and political subdivisions (municipal securities) [Member] | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]    
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]    
Number of held to maturity securities in a continuous unrealized loss position 21us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ asb_LengthoftimeheldtomaturitysecuritiesareincontinuousunrealizedlosspositionAxis
= asb_HeldtomaturitysecuritiesinunrealizedlosspositionsqualitativedisclosurenumberofpositionsgreaterthanorequaltooneyearMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
85us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ asb_LengthoftimeheldtomaturitysecuritiesareincontinuousunrealizedlosspositionAxis
= asb_HeldtomaturitysecuritiesinunrealizedlosspositionsqualitativedisclosurenumberofpositionsgreaterthanorequaltooneyearMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Government-Sponsored Enterprise (GSE) [Member]    
Unrealized losses and fair value of available for sale securities , by investment category and time length    
Unrealized losses on available for sale securities, less than 12 months (805)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
(1,404)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Unrealized losses on available for sale securities, 12 months or more (10,452)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
(29,146)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Total unrealized losses on available for sale securities (11,257)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
(30,550)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Fair value of unrealized losses on available for sale securities, less than 12 months 204,345us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
333,713us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Fair value of unrealized losses on available for sale securities, 12 months or more 1,060,452us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
1,256,533us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Total fair value of unrealized losses on available for sale securities 1,264,797us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
1,590,246us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Number of available for sale securities in a continuous unrealized loss position less than twelve months 22us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
16us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Number of available for sale securities in a continuous unrealized loss position for twelve months or more 43us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
56us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Private Label [Member]    
Unrealized losses and fair value of available for sale securities , by investment category and time length    
Unrealized losses on available for sale securities, less than 12 months (9)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
(9)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Unrealized losses on available for sale securities, 12 months or more (1)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
(1)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Total unrealized losses on available for sale securities (10)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
(10)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Fair value of unrealized losses on available for sale securities, less than 12 months 1,750us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
1,772us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Fair value of unrealized losses on available for sale securities, 12 months or more 24us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
27us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Total fair value of unrealized losses on available for sale securities 1,774us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
1,799us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Number of available for sale securities in a continuous unrealized loss position less than twelve months 1us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
1us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Number of available for sale securities in a continuous unrealized loss position for twelve months or more 2us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
2us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
GSE commercial mortgage-related securities [Member]    
Unrealized losses and fair value of available for sale securities , by investment category and time length    
Unrealized losses on available for sale securities, less than 12 months (95)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
(1,766)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionlessthan12monthsaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Unrealized losses on available for sale securities, 12 months or more (14,980)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
(24,176)asb_Availableforsalesecuritiescontinuousunrealizedlossposition12monthsorlongeraccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Total unrealized losses on available for sale securities (15,075)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
(25,942)asb_Availableforsalesecuritiescontinuousunrealizedlosspositionaccumulatedloss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Fair value of unrealized losses on available for sale securities, less than 12 months 99,052us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
329,982us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Fair value of unrealized losses on available for sale securities, 12 months or more 455,874us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
460,425us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Total fair value of unrealized losses on available for sale securities $ 554,926us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
$ 790,407us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Number of available for sale securities in a continuous unrealized loss position less than twelve months 4us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
9us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Number of available for sale securities in a continuous unrealized loss position for twelve months or more 20us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
20us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember