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Stock-Based Compensation - Performance-Based Restricted Stock Activity (Detail) - Performance-Based Restricted Stock and Performance-Based Restricted Stock Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Restricted Stock Activity [Line Items]
Nonvested, Shares, Beginning Balance	123,656	182,412	233,316
Performance-based Restricted Stock, Granted	78,404	164,270	161,140
Performance-based Restricted Stock, Vested	(128,762)	(222,004)	(212,044)
Performance-based Restricted Stock, Forfeited	(728)	(1,022)
Nonvested, Shares, Ending Balance	72,570	123,656	182,412
Nonvested, Weighted-Average Grant Price Per Share, Beginning Balance	$ 30.67	$ 18.43	$ 12.93
Weighted-Average Grant Price Per Share, Granted	39.60	23.82	17.63
Weighted-Average Grant Price Per Share, Vested	28.87	15.55	11.76
Weighted-Average Grant Price Per Share, Forfeited	41.12	29.23
Nonvested, Weighted-Average Grant Price Per Share, Ending Balance	$ 43.42	$ 30.67	$ 18.43

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Schedule of restricted stock activity.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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