Regulatory Requirements and Subsidiary Dividend Restrictions Regulatory Requirements and Subsidiary Dividend Restrictions - Customer Reserve Requirements (Details) $ in Millions	Sep. 30, 2019 USD ($)
Customer Reserve Requirement [Member] [Member]
Cash Reserve Deposit Required	$ 19.4
Cash Reserve Deposit Required and Made	21.4
PAB Reserve Requirement [Member]
Cash Reserve Deposit Required	2.6
Cash Reserve Deposit Required and Made	$ 3.6

Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 305
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6478312&loc=d3e61473-112792

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