Commitments and Contingent Liabilities - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Unfunded commitments - LLC Investments	$ 37.5	$ 20.3

Unused amount of commitments to extend credit to customers.

No definition available.

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