Earnings per Share - Composition of Weighted-Average Common Shares (Denominator) Used in Basic and Diluted Earnings Per Share (Detail) - shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Weighted Average Number of Shares, Deferred Compensation Plans	37,411	37,411	0
Weighted average common shares issued	113,914,902	111,809,880	105,563,455
Average treasury shares	(14,747,687)	(16,463,079)	(16,605,461)
Average unearned nonvested shares	(93,641)	(89,334)	(106,421)
Weighted average common shares and common stock equivalents used to calculate basic earnings per share	99,036,163	95,220,056	88,851,573
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share	149,939	73,570	0
Weighted average common shares and common stock equivalents used to calculate diluted earnings per share	99,223,513	95,331,037	88,851,573
Weighted Average Number Of Additional Shares Deferred Compensation Plan	37,411	37,411	0

Weighted Average Number Of Additional Shares Deferred Compensation Plan

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Weighted average number of additional shares non vested.

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Weighted average number of shares issued, basic and diluted.

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Weighted Average Number of Shares, Deferred Compensation Plans

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- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1505-109256

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Shares issuable for little or no cash consideration upon the satisfaction of certain conditions (contingently issuable shares) are considered outstanding common shares and included in the computation of basic Earnings Per Share as of the date that all necessary conditions have been satisfied (in essence, when issuance of the shares is no longer contingent). Outstanding common shares that are contingently returnable (that is, subject to recall) are treated in the same manner as contingently issuable shares. Contingently issuable shares include shares that (a) will be issued in the future upon the satisfaction of specified conditions, (b) have been placed in escrow and all or part must be returned if specified conditions are not met, or (c) have been issued but the holder must return all or part if specified conditions are not met. The number of contingently issuable shares is determined by relating the portion of time within a reporting period that these shares have been outstanding to the total time in that period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 13
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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 10
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- Definition

Number of shares of treasury stock determined by relating the portion of time within a reporting period that treasury shares have been outstanding to the total time in that period. Treasury stock is stock that the Entity has issued but subsequently reacquired.

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