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Restricted Stock Units Issued (Detail) - Restricted Stock Units (RSUs) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Restricted Stock Units
Beginning Restricted Stock Units	23,576	14,903
Restricted Stock Units Granted	8,965	9,078
Dividend Equivalents Earned	1,047	701
Restricted Stock Units Settled		(1,106)
Ending Restricted Stock Units	33,588	23,576
Weighted-Average Stock Price
Beginning Restricted Stock Units	$ 29.90	$ 28.90
Restricted Stock Units Granted	36.54	31.23
Dividend Equivalents Earned	35.01	33.18
Restricted Stock Units Settled		29.49
Ending Restricted Stock Units	$ 31.83	$ 29.90

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

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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