Stock Options and Restricted Stock - Restricted Stock Activity (Detail) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
2005 Incentive Plan [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Nonvested outstanding, Beginning balance		800	1,600
Shares, Vested		(800)	(800)
Shares, Nonvested outstanding, Ending balance			800
Weighted-Average Grant-Date Fair Value per Share, Beginning balance		$ 27.35	$ 27.35
Weighted-Average Grant-Date Fair Value per Share, Vested		$ 27.35	27.35
Weighted-Average Grant-Date Fair Value per Share, Ending balance			$ 27.35
2012 Incentive Plan [Member] \| Common and Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Nonvested outstanding, Beginning balance	60,879	76,392	77,528
Shares, Granted	3,304	9,326	27,077
Shares, Vested	(24,608)	(24,839)	(26,294)
Shares, Forfeited			(1,919)
Shares, Nonvested outstanding, Ending balance	39,575	60,879	76,392
Weighted-Average Grant-Date Fair Value per Share, Beginning balance	$ 45.71	$ 43.91	$ 40.57
Weighted-Average Grant-Date Fair Value per Share, Granted	59.16	55.58	54.44
Weighted-Average Grant-Date Fair Value per Share, Vested	44.31	43.89	45.18
Weighted-Average Grant-Date Fair Value per Share, Ending balance	$ 48.93	$ 45.71	$ 43.91
Non-Employee Director Restricted Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Nonvested outstanding, Beginning balance	6,454	5,576	7,112
Shares, Granted	5,761	6,454	5,952
Shares, Vested	(6,454)	(5,576)	(7,488)
Shares, Nonvested outstanding, Ending balance	5,761	6,454	5,576
Weighted-Average Grant-Date Fair Value per Share, Beginning balance	$ 54.20	$ 64.50	$ 44.26
Weighted-Average Grant-Date Fair Value per Share, Granted	60.75	54.20	63.57
Weighted-Average Grant-Date Fair Value per Share, Vested	54.20	64.50	44.54
Weighted-Average Grant-Date Fair Value per Share, Ending balance	$ 60.75	$ 54.20	$ 64.50

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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-Paragraph 2
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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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-Publisher FASB
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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

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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-Publisher FASB
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- Definition

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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No definition available.

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