Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Undisbursed loans and unused lines of credit
Financial Instruments with Off-Balance Sheet Risk
Allowance for credit losses	$ 3.3	$ 4.6
Commitments to extend credit
Financial Instruments with Off-Balance Sheet Risk
Financial instruments with off-balance sheet risk	1,580.0	$ 1,830.0
Undisbursed Commitments For C&I Loans
Financial Instruments with Off-Balance Sheet Risk
Financial instruments with off-balance sheet risk	$ 1,100.0

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant