Regulatory - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Regulatory Capital Requirements [Abstract]
Description of minimum net capital requirements	The greater of $5,000 or 1/15 of aggregate indebtedness
Minimum net capital requirements (greater than $5,000 or 1/15 of aggregate indebtedness)	$ 5,000
Minimum net capital requirements (greater than $5,000 or 1/15 of aggregate indebtedness)	6.67%
Net capital	$ 5,000,000	$ 7,300,000
Excess net capital	$ 4,000,000	$ 5,900,000
Aggregate indebtedness to net capital ratio	3.03	2.80

Minimum Net Capital Required For Broker Dealer Subsidiary, Percent of Aggregate Indebtedness

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- Definition

Describes the capital requirements for trusts assets under management.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65217-112826

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- Definition

The amount of net capital in excess of the minimum required net capital.

+ References

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

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- Definition

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

+ References

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

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- Definition

Net capital is equal to the net worth of the broker dealer, less certain items such as exchange memberships, carrying value of securities not readily marketable, haircuts on marketable securities in proprietary accounts, furniture and equipment and other illiquid assets as defined.

+ References

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

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- Definition

Indebtedness divided by net capital.

+ References

No definition available.

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- References

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