Stock-Based Compensation - Summary of Stock-Based Compensation Grants (Detail) (USD $)	6 Months Ended
Jun. 30, 2013
Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted	60,306
Weighted-Average Grant Price Per Share	$ 43.87
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted	39,660
Weighted-Average Grant Price Per Share	$ 43.88

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).

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

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration