Borrowed Funds - Components of Long-Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2020
Marquette Capital Trust I Subordinated Debentures 1.57% due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	1.57%
Debt instrument, maturity year	2036
Marquette Capital Trust II Subordinated Debentures 1.57% due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	1.57%
Debt instrument, maturity year	2036
Marquette Capital Trust III Subordinated Debentures 1.74% due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	1.74%
Debt instrument, maturity year	2036
Marquette Capital Trust IV Subordinated Debentures 1.82% due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	1.82%
Debt instrument, maturity year	2036
Subordinated notes 3.70% due 2030, net of issuance costs [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	3.70%
Debt instrument, maturity year	2030