Fair Value, Assets, Level 3 to Level 2 Transfers, Amount

No definition available.

Name:	asb_FairValueAssetsLevel3toLevel2TransfersAmount
Namespace Prefix:	asb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Net Mortgage Derivative Gain (Loss) Included In Earnings.

+ References

No definition available.

+ Details

Name:	asb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetNetMortgageDerivativeGainLossIncludedInEarnings
Namespace Prefix:	asb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19279-110258

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_SecuritiesAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=asb_DerivativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value Measurements, Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Investment Securities Available for Sale
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Fair Value, Assets, Level 3 to Level 2 Transfers, Amount			$ (200)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Assets, Level 3 to Level 2 Transfers, Amount			$ 200
Derivative Financial Instruments
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Mortgage derivative gain (loss)	$ (1,085)	$ (1,889)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	1,225	3,114
Mortgage derivative gain (loss)	(1,085)	(1,889)
Ending Balance	140	1,225
Available-for-sale Securities [Member]
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Beginning Balance	0	(200)
Mortgage derivative gain (loss)	0	0
Ending Balance	0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Mortgage derivative gain (loss)	$ 0	0
Fair Value, Measurements, Recurring [Member] \| Derivative Financial Instruments
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Fair Value, Assets, Level 3 to Level 2 Transfers, Amount		0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Assets, Level 3 to Level 2 Transfers, Amount		0
Fair Value, Measurements, Recurring [Member] \| Available-for-sale Securities [Member]
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Fair Value, Assets, Level 3 to Level 2 Transfers, Amount		(200)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Assets, Level 3 to Level 2 Transfers, Amount		$ 200