Net Capital Requirements - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($)
Net Capital Requirements [Abstract]
Percentage of aggregate debit items arising from customer transactions to maintain minimum net capital requirements	2.00%
Minimum net capital requirements	$ 250,000

Minimum amount of net capital required to be maintained by entity's broker-dealer subsidiary to engage in securities transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

Name:	us-gaap_MinimumNetCapitalRequiredForBrokerDealerSubsidiary1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant