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Stock-Based Compensation - Schedule of Restricted Stock Unit Programs Outstanding (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity Classified RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding, Beginning Balance	367,726	181,732	184,084
Granted	320,131	208,458	20,940
Dividend equivalents	1,895	2,022	946
Redeemed	(84,322)	(24,486)	(24,238)
Number of options outstanding, Ending Balance	605,430	367,726	181,732
Liability Classified RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding, Beginning Balance	29,806	34,242	12,272
Granted	15,364	4,150	26,000
Dividend equivalents	1,133	946	391
Redeemed	(26,204)	(9,532)	(4,421)
Number of options outstanding, Ending Balance	20,099	29,806	34,242
Liability Classified DSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding, Beginning Balance	198,446	186,348	153,013
Granted	37,456	22,669	40,954
Dividend equivalents	5,145	4,696	1,758
Redeemed	(34,124)	(15,267)	(9,377)
Number of options outstanding, Ending Balance	206,923	198,446	186,348
Release of restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding, Beginning Balance	595,978	402,322	349,369
Granted	372,951	235,277	87,894
Dividend equivalents	8,173	7,664	3,095
Redeemed	(144,650)	(49,285)	(38,036)
Number of options outstanding, Ending Balance	832,452	595,978	402,322

X

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options dividend equivalents in period.

+ References

No definition available.

+ Details

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X

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options redeemed in period.

+ References

No definition available.

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X

- 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

-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=6415400&loc=d3e5070-113901



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(c)

-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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X

- 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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(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.



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(a)

-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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