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Employee Benefits - Summary of Nonvested Common Stock Awards and Changes During Period (Detail)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Retirement Benefits [Abstract]
Nonvested common stock awards, Beginning balance | shares	161,174
Granted | shares	101,241
Vested | shares	(57,816)
Forfeited | shares	(1,157)
Nonvested common stock awards, Ending balance | shares	203,442
Nonvested common stock awards, Beginning balance | $ / shares	$ 26.36
Granted | $ / shares	52.00
Vested | $ / shares	26.30
Forfeited | $ / shares	31.13
Nonvested common stock awards, Ending balance | $ / shares	$ 39.11

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ 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 (d)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Number of non-vested options outstanding.

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Number of non-vested options forfeited.

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Weighted average grant-date fair value of non-vested options forfeited.

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Weighted average grant-date fair value of non-vested options outstanding.

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