Investment Securities - Additional disclosures (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Additional disclosures
Carrying value of investment securities pledged to secure public funds deposits and for other purposes required and permitted by law	$ 726.1	$ 888.8
Carrying amount of the securities pledged to collateralize repurchase agreements	$ 242.2	$ 205.3

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Name:	us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesForRepurchaseAgreements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant