Fair Value Measurements Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financial assets
Cash and due from banks	$ 303,701	$ 444,113
Cash and due from banks, Fair Value	303,701	444,113
Interest-bearing deposits in other financial institutions	70,023	571,924
Interest-bearing deposits in other financial institutions, Fair value	70,023	571,924
Federal funds sold and securities purchased under agreements to resell	36,490	16,030
Federal funds sold and securities purchased under agreements to resell, Fair value	36,490	16,030
Investment securities held to maturity, carrying amount	604,799	404,455
Fair value	613,372	413,067
Investment securities available for sale, at fair value	5,403,656	5,396,812
Investment securities available for sale, fair value	5,403,656	5,396,812
Federal Home Loan Bank and Federal Reserve Bank stocks, carrying amount	160,871	189,107
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	160,871	189,107
Loans held for sale	105,144	154,935
Loans held for sale, fair value	106,276	156,423
Loans, net	18,262,237	17,327,544
Loans, net Fair value	18,435,809	17,427,647
Bank owned life insurance, carrying amount	580,289	574,154
Bank owned life insurance, Fair value	580,289	574,154
Accrued interest receivable, carrying amount	70,977	67,573
Accrued interest receivable, Fair value	70,977	67,573
Interest rate-related agreements, carrying amount	42,593	33,023
Interest rate-related agreements, fair value	42,593	33,023
Foreign currency exchange forwards	1,159	2,140
Foreign currency exchange forwards, Fair value	1,159	2,140
Interest rate lock commitments to originate residential mortgage loans held for sale	2,584	1,947
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	2,584	1,947
Purchased options (time deposit), carrying value	2,915	6,054
Purchased options (time deposit), fair value	2,915	6,054
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits	18,936,600	17,192,049
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	18,936,600	17,192,049
Brokered CDs and other time deposits	1,621,795	1,571,455
Brokered CDs and other time deposits, Fair value	1,632,811	1,571,455
Short-term funding	1,022,335	1,068,288
Short-term funding, Fair value	1,022,335	1,068,288
Long-term funding	2,679,542	3,930,117
Long-term funding, fair value	2,740,335	3,975,605
Accrued interest payable	6,888	9,530
Accrued interest payable, Fair value	6,888	9,530
Interest rate-related agreements	44,857	35,372
Interest rate-related agreements, Fair value	44,857	35,372
Foreign currency exchange forwards	960	1,957
Foreign currency exchange forwards, Fair value	960	1,957
Standby letters of credit, carrying amount	3,164	3,542
Standby letters of credit, Fair value	3,164	3,542
Forward commitments to sell residential mortgage loans	1,982	2,435
Forward commitments to sell residential mortgage loans, fair value	1,982	2,435
Written options (time deposit), carrying value	2,915	6,054
Written option (time deposit), fair value	2,915	6,054
Fair Value, Inputs, Level 1 [Member]
Financial assets
Cash and due from banks, Fair Value	303,701	444,113
Interest-bearing deposits in other financial institutions, Fair value	70,023	571,924
Federal funds sold and securities purchased under agreements to resell, Fair value	36,490	16,030
Fair value	0	0
Investment securities available for sale, fair value	4,505	3,957
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	0	0
Loans held for sale, fair value	0	0
Loans, net Fair value	0	0
Bank owned life insurance, Fair value	0	0
Accrued interest receivable, Fair value	70,977	67,573
Interest rate-related agreements, fair value	0	0
Foreign currency exchange forwards, Fair value	0	0
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	0	0
Purchased options (time deposit), fair value	0	0
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	0	0
Brokered CDs and other time deposits, Fair value	0	0
Short-term funding, Fair value	0	0
Long-term funding, fair value	0	0
Accrued interest payable, Fair value	6,888	9,530
Interest rate-related agreements, Fair value	0	0
Foreign currency exchange forwards, Fair value	0	0
Standby letters of credit, Fair value	0	0
Forward commitments to sell residential mortgage loans, fair value	0	0
Written option (time deposit), fair value	0	0
Fair Value, Inputs, Level 2 [Member]
Financial assets
Cash and due from banks, Fair Value	0	0
Interest-bearing deposits in other financial institutions, Fair value	0	0
Federal funds sold and securities purchased under agreements to resell, Fair value	0	0
Fair value	613,372	413,067
Investment securities available for sale, fair value	5,398,951	5,392,655
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	160,871	189,107
Loans held for sale, fair value	106,276	156,423
Loans, net Fair value	0	0
Bank owned life insurance, Fair value	580,289	574,154
Accrued interest receivable, Fair value	0	0
Interest rate-related agreements, fair value	42,593	33,023
Foreign currency exchange forwards, Fair value	1,159	2,140
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	0	0
Purchased options (time deposit), fair value	2,915	6,054
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	0	0
Brokered CDs and other time deposits, Fair value	1,632,811	1,571,455
Short-term funding, Fair value	1,022,335	1,068,288
Long-term funding, fair value	2,740,335	3,975,605
Accrued interest payable, Fair value	0	0
Interest rate-related agreements, Fair value	44,857	35,372
Foreign currency exchange forwards, Fair value	960	1,957
Standby letters of credit, Fair value	3,164	3,542
Forward commitments to sell residential mortgage loans, fair value	0	0
Written option (time deposit), fair value	2,915	6,054
Fair Value, Inputs, Level 3 [Member]
Financial assets
Cash and due from banks, Fair Value	0	0
Interest-bearing deposits in other financial institutions, Fair value	0	0
Federal funds sold and securities purchased under agreements to resell, Fair value	0	0
Fair value	0	0
Investment securities available for sale, fair value	200	200
Federal Home Loan Bank and Federal Reserve Bank stocks, Fair value	0	0
Loans held for sale, fair value	0	0
Loans, net Fair value	18,435,809	17,427,647
Bank owned life insurance, Fair value	0	0
Accrued interest receivable, Fair value	0	0
Interest rate-related agreements, fair value	0	0
Foreign currency exchange forwards, Fair value	0	0
Interest rate lock commitments to originate residential mortgage loans held for sale, fair value	2,584	1,947
Purchased options (time deposit), fair value	0	0
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, Fair value	18,936,600	17,192,049
Brokered CDs and other time deposits, Fair value	0	0
Short-term funding, Fair value	0	0
Long-term funding, fair value	0	0
Accrued interest payable, Fair value	0	0
Interest rate-related agreements, Fair value	0	0
Foreign currency exchange forwards, Fair value	0	0
Standby letters of credit, Fair value	0	0
Forward commitments to sell residential mortgage loans, fair value	1,982	2,435
Written option (time deposit), fair value	$ 0	$ 0

Accrued interest receivable fair value disclosure.

No definition available.

Name:	asb_AccruedInterestReceivableFairValueDisclosure
Namespace Prefix:	asb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References

No definition available.