Income Taxes (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	$ 25,600
Income tax expense (benefit), intraperiod tax allocation	$ 31,420	$ 14,522	$ 14,802
Effective tax rate, Statutory federal tax	21.00%	21.00%	21.00%
Income tax expense	$ 31,406	$ 14,447	$ 14,759
Effective tax rate, Share-based compensation	(0.30%)	(7.00%)	(2.60%)
Maryland State [Member]
Tax Credit Carryforward [Line Items]
Operating loss carryforwards expiration year	2029

Operating loss carryforwards expiration year.

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

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of income tax expense (benefit) for continuing operations, discontinued operations, other comprehensive income, and items charged (credited) directly to shareholders' equity.

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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