Share-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	831,183
Granted awards, shares	953
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 2,200
SICP Awards to Non-employee directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amortization of expense equally over a service period	1 year
Unrecognized compensation expense related to the awards to Non employee directors	$ 180
Granted awards, shares	8,577	14,484
Weighted average grant-date fair value of awards granted	$ 62.90	$ 45.54	$ 41.60
SICP Awards to Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted awards, shares	46,571	33,719
Number of shares withheld	12,031	12,620	12,687
Payments of employees' tax obligations to taxing authorities	$ 770	$ 592	$ 503
Weighted average grant-date fair value of awards granted	$ 67.90	$ 47.65	$ 39.99
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Nonvested	$ 7,700	$ 6,300	$ 6,100
Additional Paid-In Capital [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	$ (285)	$ 297	$ 398
Stock and Incentive Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	539,374

Period for amortization of share based expenses.

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- Definition

Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 740
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65880886&loc=d3e23524-113945

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

+ References

No definition available.

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- Definition

Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
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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://www.xbrl.org/2003/role/presentationRef
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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
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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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- Definition

Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

+ References

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- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

+ References

No definition available.

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