Stock Option Activity (Detail)	6 Months Ended
Jun. 30, 2018 $ / shares shares
Shares
Outstanding at beginning of period \| shares	6,037,150
Exercised \| shares	(40,000)
Expired \| shares	(496,000)
Outstanding at end of period \| shares	5,501,150
Exercisable at end of year \| shares	5,206,454
Weighted Average Exercise Price Per Share
Outstanding at beginning of period \| $ / shares	$ 20.35
Exercised \| $ / shares	12.12
Expired \| $ / shares	29.01
Outstanding at end of period \| $ / shares	19.63
Exercisable at end of year \| $ / shares	$ 19.69

No definition available.

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- Definition

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.

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

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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- Definition

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

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- Definition

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

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