Loans, Allowance for Credit Losses and Impaired Loans - Concentration Risk (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Loans, Allowance for Credit Losses and Impaired Loans
Commitments to loan additional funds	$ 0.0	$ 0.0

Reflects the carrying amount of loans and leases for which agreements to acquire or dispose exist.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 825
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=108315417&loc=d3e61044-112788

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 825
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=108315417&loc=d3e61082-112788

Name:	us-gaap_LoansAndLeasesReceivableCommitmentsToPurchaseOrSell
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration