Loans, Allowance for Loan Losses, and Credit Quality Impaired Loans Recorded Investment, Unpaid Principal Balance, Related Allowance, Average Recorded Investment, and Interest Income Recognized (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	$ 275,629	$ 309,413
Unpaid Principal Balance	310,811	361,694
Related Allowance	50,431	51,875
Average Recorded Investment	290,370	328,022
Interest Income Recognized	9,384	10,137
FairValueMark	72.00%asb_Fairvaluemark	71.00%asb_Fairvaluemark
Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	232,166	250,263
Unpaid Principal Balance	253,186	283,066
Related Allowance	50,431	51,875
Average Recorded Investment	242,219	264,784
Interest Income Recognized	8,797	9,186
Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	43,463	59,150
Unpaid Principal Balance	57,625	78,628
Related Allowance	0	0
Average Recorded Investment	48,151	63,238
Interest Income Recognized	587	951
Commercial And Industrial Financing Receivable [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	83,555	70,236
Unpaid Principal Balance	93,048	84,999
Related Allowance	16,467	11,917
Average Recorded Investment	88,855	75,291
Interest Income Recognized	3,221	2,047
Commercial And Industrial Financing Receivable [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	76,433	57,857
Unpaid Principal Balance	80,414	65,443
Related Allowance	16,467	11,917
Average Recorded Investment	80,004	61,000
Interest Income Recognized	3,139	1,741
Commercial And Industrial Financing Receivable [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	7,122	12,379
Unpaid Principal Balance	12,634	19,556
Related Allowance	0	0
Average Recorded Investment	8,851	14,291
Interest Income Recognized	82	306
Commercial Real Estate Owner Occupied Portfolio [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	36,279	42,673
Unpaid Principal Balance	40,826	47,903
Related Allowance	3,221	2,955
Average Recorded Investment	38,848	45,151
Interest Income Recognized	900	1,310
Commercial Real Estate Owner Occupied Portfolio [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	19,839	22,651
Unpaid Principal Balance	21,807	25,072
Related Allowance	3,221	2,955
Average Recorded Investment	20,878	24,549
Interest Income Recognized	681	995
Commercial Real Estate Owner Occupied Portfolio [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	16,440	20,022
Unpaid Principal Balance	19,019	22,831
Related Allowance	0	0
Average Recorded Investment	17,970	20,602
Interest Income Recognized	219	315
Finance Leases Financing Receivable [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,801	69
Unpaid Principal Balance	1,801	69
Related Allowance	574	29
Average Recorded Investment	2,009	76
Interest Income Recognized	0	0
Finance Leases Financing Receivable [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,801	69
Unpaid Principal Balance	1,801	69
Related Allowance	574	29
Average Recorded Investment	2,009	76
Interest Income Recognized	0	0
Finance Leases Financing Receivable [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Commercial And Business Lending [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	121,635	112,978
Unpaid Principal Balance	135,675	132,971
Related Allowance	20,262	14,901
Average Recorded Investment	129,712	120,518
Interest Income Recognized	4,121	3,357
Commercial And Business Lending [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	98,073	80,577
Unpaid Principal Balance	104,022	90,584
Related Allowance	20,262	14,901
Average Recorded Investment	102,891	85,625
Interest Income Recognized	3,820	2,736
Commercial And Business Lending [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	23,562	32,401
Unpaid Principal Balance	31,653	42,387
Related Allowance	0	0
Average Recorded Investment	26,821	34,893
Interest Income Recognized	301	621
Commercial Real Estate Investor Portfolio Segment [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	45,812	82,542
Unpaid Principal Balance	54,905	93,677
Related Allowance	3,587	7,895
Average Recorded Investment	48,671	88,130
Interest Income Recognized	1,383	2,865
Commercial Real Estate Investor Portfolio Segment [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	36,841	64,647
Unpaid Principal Balance	40,869	68,228
Related Allowance	3,587	7,895
Average Recorded Investment	38,657	68,776
Interest Income Recognized	1,250	2,735
Commercial Real Estate Investor Portfolio Segment [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	8,971	17,895
Unpaid Principal Balance	14,036	25,449
Related Allowance	0	0
Average Recorded Investment	10,014	19,354
Interest Income Recognized	133	130
Commercial Real Estate Construction Financing Receivable [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	6,126	10,260
Unpaid Principal Balance	9,725	14,388
Related Allowance	1,095	2,416
Average Recorded Investment	7,059	11,372
Interest Income Recognized	105	249
Commercial Real Estate Construction Financing Receivable [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	3,043	8,815
Unpaid Principal Balance	5,910	12,535
Related Allowance	1,095	2,416
Average Recorded Investment	3,818	9,796
Interest Income Recognized	105	236
Commercial Real Estate Construction Financing Receivable [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	3,083	1,445
Unpaid Principal Balance	3,815	1,853
Related Allowance	0	0
Average Recorded Investment	3,241	1,576
Interest Income Recognized	0	13
Commercial Real Estate Lending [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	51,938	92,802
Unpaid Principal Balance	64,630	108,065
Related Allowance	4,682	10,311
Average Recorded Investment	55,730	99,502
Interest Income Recognized	1,488	3,114
Commercial Real Estate Lending [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	39,884	73,462
Unpaid Principal Balance	46,779	80,763
Related Allowance	4,682	10,311
Average Recorded Investment	42,475	78,572
Interest Income Recognized	1,355	2,971
Commercial Real Estate Lending [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	12,054	19,340
Unpaid Principal Balance	17,851	27,302
Related Allowance	0	0
Average Recorded Investment	13,255	20,930
Interest Income Recognized	133	143
Commercial Financing Receivable [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	173,573	205,780
Unpaid Principal Balance	200,305	241,036
Related Allowance	24,944	25,212
Average Recorded Investment	185,442	220,020
Interest Income Recognized	5,609	6,471
Commercial Financing Receivable [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	137,957	154,039
Unpaid Principal Balance	150,801	171,347
Related Allowance	24,944	25,212
Average Recorded Investment	145,366	164,197
Interest Income Recognized	5,175	5,707
Commercial Financing Receivable [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	35,616	51,741
Unpaid Principal Balance	49,504	69,689
Related Allowance	0	0
Average Recorded Investment	40,076	55,823
Interest Income Recognized	434	764
Home Equity [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	31,807	34,800
Unpaid Principal Balance	35,533	40,436
Related Allowance	13,015	13,989
Average Recorded Investment	33,226	36,717
Interest Income Recognized	1,528	1,520
Home Equity [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	31,021	34,707
Unpaid Principal Balance	34,727	40,344
Related Allowance	13,015	13,989
Average Recorded Investment	32,375	36,623
Interest Income Recognized	1,510	1,518
Home Equity [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	786	93
Unpaid Principal Balance	806	92
Related Allowance	0	0
Average Recorded Investment	851	94
Interest Income Recognized	18	2
Installment and Credit Cards [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,587	1,360
Unpaid Principal Balance	1,795	1,676
Related Allowance	308	487
Average Recorded Investment	1,736	1,753
Interest Income Recognized	58	100
Installment and Credit Cards [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	1,587	1,360
Unpaid Principal Balance	1,795	1,676
Related Allowance	308	487
Average Recorded Investment	1,736	1,753
Interest Income Recognized	58	100
Installment and Credit Cards [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Residential, Prime, Financing Receivable [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	68,662	67,473
Unpaid Principal Balance	73,178	78,546
Related Allowance	12,164	12,187
Average Recorded Investment	69,966	69,532
Interest Income Recognized	2,189	2,046
Residential, Prime, Financing Receivable [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	61,601	60,157
Unpaid Principal Balance	65,863	69,699
Related Allowance	12,164	12,187
Average Recorded Investment	62,742	62,211
Interest Income Recognized	2,054	1,861
Residential, Prime, Financing Receivable [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	7,061	7,316
Unpaid Principal Balance	7,315	8,847
Related Allowance	0	0
Average Recorded Investment	7,224	7,321
Interest Income Recognized	135	185
Consumer Loan [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	102,056	103,633
Unpaid Principal Balance	110,506	120,658
Related Allowance	25,487	26,663
Average Recorded Investment	104,928	108,002
Interest Income Recognized	3,775	3,666
Consumer Loan [Member] \| Loans With Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	94,209	96,224
Unpaid Principal Balance	102,385	111,719
Related Allowance	25,487	26,663
Average Recorded Investment	96,853	100,587
Interest Income Recognized	3,622	3,479
Consumer Loan [Member] \| Loans With No Related Allowance [Member]
Summarize of nonaccrual loans, accruing loans past due 90 days or more, and restructured loans
Recorded Investment	7,847	7,409
Unpaid Principal Balance	8,121	8,939
Related Allowance	0	0
Average Recorded Investment	8,075	7,415
Interest Income Recognized	$ 153	$ 187

Loans, Allowance for Loan Losses, and Credit Quality Impaired Loans Recorded Investment, Unpaid Principal Balance, Related Allowance, Average Recorded Investment, and Interest Income Recognized (Details) (USD $)
In Thousands, unless otherwise specified