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Restricted Stock Units Issued (Detail) - Restricted Stock Units (RSUs)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Restricted Stock Units
Beginning Restricted Stock Units | shares	52,224
Restricted Stock Units Granted | shares	0
Dividend Equivalents Earned | shares	850
Restricted Stock Units Settled | shares	0
Ending Restricted Stock Units | shares	53,074
Weighted-Average Stock Price
Beginning Restricted Stock Units | $ / shares	$ 36.22
Restricted Stock Units Granted | $ / shares	0
Dividend Equivalents Earned | $ / shares	45.05
Restricted Stock Units Settled | $ / shares	0
Ending Restricted Stock Units | $ / shares	$ 36.36

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://fasb.org/us-gaap/role/ref/legacyRef
-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=109197908&loc=d3e5070-113901

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- Definition

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+ References

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- Definition

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- Definition

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- Definition

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