Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Settlement days of bond transaction	within one to two trading days
Collateral deposits	$ 4.1	$ 1.1

Carrying value of amounts transferred to third parties for security purposes that are expected to be returned or applied towards payment in the future.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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