Stock Compensation Plans - Information Regarding Activity in Stock Option Plans (Detail) - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Number of Options, Outstanding Beginning Balance	9,338,648	8,794,952	8,183,430
Number of Options, Granted	943,000	1,417,500	1,710,500
Number of Options, Exercised	(924,019)	(832,467)	(983,370)
Number of Options, Forfeited	(93,167)	(41,337)	(114,967)
Number of Options, Expired			(641)
Number of Options, Outstanding Ending Balance	9,264,462	9,338,648	8,794,952
Number of Options, Exercisable	6,946,677	6,347,470	5,250,338
Weighted-Average Exercise Price Per Share, Outstanding Beginning Balance	$ 14.95	$ 14.57	$ 14.69
Weighted-Average Exercise Price Per Share, Granted	17.58	16.44	13.64
Weighted-Average Exercise Price Per Share, Exercised	14.45	13.44	13.91
Weighted-Average Exercise Price Per Share, Forfeited	15.43	14.97	15.30
Weighted-Average Exercise Price Per Share, Expired			14.00
Weighted-Average Exercise Price Per Share, Outstanding Ending Balance	15.26	14.95	14.57
Weighted-Average Exercise Price Per Share, Exercisable	$ 14.90	$ 14.77	$ 14.42

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ References

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-Publisher FASB
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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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