Share-based Compensation - Summary of Information Activity on SARs Settled in Stock (Detail) (USD $)	1 Months Ended	12 Months Ended
Sep. 06, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested stock Options, Balance, beginning of year		412,943	447,693	518,275
Stock-settled SARs Outstanding, Granted				62,475
Stock-settled SARs Outstanding, Exercised	18,333	28,999	14,000	16,408
Stock-settled SARs Outstanding, Forfeited or expired		(16,038)	(20,750)	(116,649)
Non-vested stock Options, Balance, end of year		367,906	412,943	447,693
Stock-settled SARs exercisable, end of year		312,020	295,168	249,177
Weighted Average Exercise Price, Balance, beginning of year		$ 13.74	$ 13.61	$ 13.85
Weighted Average Exercise Price, Granted				$ 11.30
Weighted Average Exercise Price, Exercised		$ 6.83	$ 6.38	$ 6.37
Weighted Average Exercise Price, Forfeited or expired		$ 16.86	$ 15.81	$ 14.46
Weighted Average Exercise Price, Balance, end of year		$ 14.15	$ 13.74	$ 13.61
Weighted Average Exercise Price, Option exercisable, end of year		$ 14.60	$ 14.36	$ 14.15
Stock-settled SARs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested stock Options, Balance, beginning of year		405,340	460,915	401,188
Stock-settled SARs Outstanding, Granted				130,499
Stock-settled SARs Outstanding, Exercised
Stock-settled SARs Outstanding, Forfeited or expired		(18,268)	(55,575)	(70,772)
Non-vested stock Options, Balance, end of year		387,072	405,340	460,915
Stock-settled SARs exercisable, end of year		309,980	247,930	183,330
Weighted Average Exercise Price, Balance, beginning of year		$ 13.71	$ 13.75	$ 14.63
Weighted Average Exercise Price, Granted				$ 11.29
Weighted Average Exercise Price, Exercised
Weighted Average Exercise Price, Forfeited or expired		$ 13.07	$ 14.06	$ 14.22
Weighted Average Exercise Price, Balance, end of year		$ 13.74	$ 13.71	$ 13.75
Weighted Average Exercise Price, Option exercisable, end of year		$ 14.28	$ 14.80	$ 15.64

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option 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)(1)(iii)

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(1)(c), d(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option 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)(1)(iii)

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- Definition

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

+ References

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- Definition

Weighted average price of options that were either forfeited or expired.

+ References

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- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

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- Definition

The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(1)(b)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

+ References

No definition available.

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance on stock options awarded.

+ References

No definition available.

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Number of share options (or share units) exercised during the current period.

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