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Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Securities transactions income tax expense	$ 171,000	$ 10,000	$ 1,400,000
Change in income tax expense (benefit) due to write down of net deferred tax asset resulting from federal tax rate change			$ 4,300,000
Federal tax rate, percentage	21.00%	21.00%	35.00%
Recognition of interest and penalties related to unrecognized tax benefits	$ 0	$ 0	$ 0
Earliest Tax Year [Member]
Income Taxes [Line Items]
Year under examination	2016	2013
Latest Tax Year [Member]
Income Taxes [Line Items]
Year under examination	2018	2015

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- Definition

Income tax expense (benefit) on securities transaction.

+ References

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Income taxes.

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- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
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Tax year that remains open to examination under enacted tax laws, in CCYY format.

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Amount of income tax expense (benefit) for remeasurement of deferred tax from change in tax rate pursuant to Tax Cuts and Jobs Act.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-Topic 740
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- Definition

Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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