Income Taxes (Narrative) (Detail) - USD ($)		12 Months Ended
Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	35.00%
Deferred tax adjustment related to reduction in U.S. federal statutory income tax rate		$ 0	$ (231,000)	$ (4,047,000)
Correction for prior year tax-exempt interest		0	0	(2,906,000)
Valuation allowance		0	0	0
Unrecognized tax benefits		$ 0	$ 0	$ 0

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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

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Amount of income tax expense (benefit) from continuing operations attributable to an adjustment of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to revisions of previously reported income tax expense (benefit).

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Amount of unrecognized tax benefits.

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