Commitments, Off-Balance Sheet Arrangements, and Legal Proceedings (Details Textuals)	Jan. 11, 2016 USD ($) loan_production_office branch	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Unfunded commitments		$ 24,000,000	$ 24,000,000
Carrying value of investments		53,000,000	52,000,000
Commitments under unconsolidated projects		62,000,000	61,000,000
Commitment term	3 years
Mortgage loan commitment	$ 196,000,000
Number of branch opening commitments | branch	1
Number of loan production offices | loan_production_office	4
Conciliation agreement cost, commitment term	4 years
Loans repurchased under make whole requests		126,000	3,000,000
Loans sold to outside investors original amount		7,900,000,000
Loans sold to outside investors remaining outstanding amount		5,700,000,000
Residential mortgage loans sold with recourse risk		60,000,000	68,000,000
Residential mortgage loans sold with credit recourse risk		122,000,000	132,000,000
The Official Committee of Unsecured Creditors of World Marketing Chicago LLC v Associated Bank [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Damages sought	$ 6,000,000
Damages sought, cash	4,000,000
Damages sought, indebtedness	1,000,000
American Funds Service Company v Associated Bank [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Damages sought	$ 600,000
Reserve for Off-balance Sheet Activities [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Unfunded commitments		24,400,000	24,400,000	$ 24,900,000
Mortgage Repurchase Reserve [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Unfunded commitments		1,264,000	1,197,000	$ 3,258,000
Standby Letters of Credit [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Lines of Credit, Fair Value Disclosure		$ 3,000,000	$ 3,000,000