Summarize Information relating to Options Outstanding (Detail) (2005 Share Plan, USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding SARS, Weighted average exercise price	$ 7.89	$ 8.89	12.53	13.27
Stock Appreciation Rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding SARS, Number of options	1,818,261	3,151,728	4,318,909	5,030,143
Outstanding SARS, Contractual life	1 year 5 months 23 days	2 years 1 month 2 days
Outstanding SARS, Weighted average exercise price	$ 7.89	$ 8.89
Stock Appreciation Rights \| Range 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding SARS, Price range, lower limit	$ 5.19	$ 5.80
Outstanding SARS, Price range, upper limit	$ 7.35	$ 8.22
Outstanding SARS, Number of options	580,833	873,064
Outstanding SARS, Contractual life	1 year 2 months 19 days	2 years 2 months 19 days
Outstanding SARS, Weighted average exercise price	$ 6.56	$ 7.33
Stock Appreciation Rights \| Range 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding SARS, Price range, lower limit	$ 7.36	$ 8.23
Outstanding SARS, Price range, upper limit	$ 9.51	$ 10.64
Outstanding SARS, Number of options	454,131	1,217,915
Outstanding SARS, Contractual life	3 months 29 days	10 months 24 days
Outstanding SARS, Weighted average exercise price	$ 8.17	$ 9.00
Stock Appreciation Rights \| Range 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding SARS, Price range, lower limit	$ 9.52	$ 10.65
Outstanding SARS, Price range, upper limit	$ 11.68	$ 13.06
Outstanding SARS, Number of options	769,159	1,033,784
Outstanding SARS, Contractual life	2 years 3 months 29 days	3 years 4 months 2 days
Outstanding SARS, Weighted average exercise price	$ 8.94	$ 10.00
Stock Appreciation Rights \| Range 4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding SARS, Price range, lower limit	$ 11.69	$ 13.07
Outstanding SARS, Price range, upper limit	$ 13.84	$ 15.47
Outstanding SARS, Number of options	14,138	26,965
Outstanding SARS, Contractual life	3 years 4 days	4 years 4 days
Outstanding SARS, Weighted average exercise price	$ 10.25	$ 11.46

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Number of options outstanding, including both vested and non-vested options.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)-(ii)

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

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance 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)(i)

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

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- Definition

Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ 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 (e)(1)

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

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- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ 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 (g)

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

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- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ 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 (g)

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

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