Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Calculations for basic and diluted earnings per common share
Net income	$ 190,509us-gaap_NetIncomeLoss	$ 188,692us-gaap_NetIncomeLoss	$ 178,973us-gaap_NetIncomeLoss
Preferred stock dividends and discount accretion	(5,002)	(5,158)	(5,200)
Net income (loss) available to common equity	185,507	183,534	173,773
Common shareholder dividends	(58,123)us-gaap_DividendsCommonStock	(54,505)us-gaap_DividendsCommonStock	(39,462)us-gaap_DividendsCommonStock
Unvested share-based payment awards	(587)asb_UnvestedShareBasedPaymentAwards	(486)asb_UnvestedShareBasedPaymentAwards	(172)asb_UnvestedShareBasedPaymentAwards
Undistributed earnings	126,797us-gaap_UndistributedEarnings	128,543us-gaap_UndistributedEarnings	134,139us-gaap_UndistributedEarnings
Undistributed earnings allocated to common shareholders	125,646	127,592	133,549
Undistributed earnings allocated to unvested share-based payment awards	1,151	951	590
Undistributed earnings	126,797us-gaap_UndistributedEarnings	128,543us-gaap_UndistributedEarnings	134,139us-gaap_UndistributedEarnings
Basic
Distributed earnings to common shareholders	58,123	54,505	39,462
Undistributed earnings to common shareholders Basic	125,646asb_Undistributedearningsbasic	127,592asb_Undistributedearningsbasic	133,549asb_Undistributedearningsbasic
Common Shareholders Earnings Basic	183,769asb_CommonShareholdersEarningsBasic	182,097asb_CommonShareholdersEarningsBasic	173,011asb_CommonShareholdersEarningsBasic
Diluted
Distributed earnings to common shareholders	58,123	54,505	39,462
Undistributed earnings to common shareholders Diluted	125,646us-gaap_UndistributedEarningsDiluted	127,592us-gaap_UndistributedEarningsDiluted	133,549us-gaap_UndistributedEarningsDiluted
Common Shareholders Earnings Diluted	$ 183,769asb_CommonShareholdersEarningsDiluted	$ 182,097asb_CommonShareholdersEarningsDiluted	$ 173,011asb_CommonShareholdersEarningsDiluted
Weighted average common shares outstanding	157,286	165,584	172,255
Effect of dilutive common stock awards	968	218	102
Diluted weighted average common shares outstanding	158,254	165,802	172,357
Basic earnings (loss) per common share	$ 1.17us-gaap_EarningsPerShareBasic	$ 1.10us-gaap_EarningsPerShareBasic	$ 1.00us-gaap_EarningsPerShareBasic
Diluted earnings (loss) per common share	$ 1.16us-gaap_EarningsPerShareDiluted	$ 1.10us-gaap_EarningsPerShareDiluted	$ 1.00us-gaap_EarningsPerShareDiluted

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Undistributed earnings allocated to common shareholders

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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