Unvested Restricted Stock Grants Outstanding (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance	626,812	587,629	526,972
Granted	288,130	269,926	244,060
Vested	(183,716)	(133,482)	(138,321)
Forfeited	(12,334)	(97,261)	(45,082)
Ending balance	718,892	626,812	587,629
Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	228,607	114,463	97,145
Performance Based Shares \| Earned
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested		(15,714)
Performance Based Shares \| Unearned
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested	(93,453)	(57,585)	(46,998)
Non Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	59,523	155,463	146,915
Vested	(90,263)	(60,183)	(91,323)

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

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)(iv)(3)

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

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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://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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(2)

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

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