Stock and Incentive Programs for Employees and Directors - Stock Options - Narrative (Detail) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options exercised	0
Unrecognized share-based compensation cost	$ 14,000,000
Stock options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	0	0
Intrinsic value of options exercised		$ 300,000	$ 800,000
Unrecognized share-based compensation cost	$ 0
Cash proceeds received from option exercises		$ 1,100,000	$ 1,800,000

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Net number of share options (or share units) granted during the period.

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Number of share options (or share units) exercised during the current period.

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