For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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

+ References

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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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No definition available.

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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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No definition available.

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

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No definition available.

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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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No definition available.

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

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Stockholders' Equity - Summary of Stock Option Activity (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Number of Shares Subject to Options
Number of Shares, Beginning balance (shares)			1,172,000
Number of Shares, Options granted (shares)	0	0	0	0
Number of Shares, Options exercised (shares)			(426,000)
Number of Shares, Options cancelled / forfeited / expired (shares)			(59,000)
Number of Shares, Ending balance (shares)	687,000		687,000
Weighted Average Exercise Price Per Share
Weighted Average Exercise Price Per Share, Beginning balance (usd per share)			$ 24.06
Weighted Average Exercise Price Per Share, Options granted (usd per share)			0.00
Weighted Average Exercise Price Per Share, Options exercised (usd per share)			18.76
Weighted Average Exercise Price Per Share, Options cancelled / forfeited / expired (usd per share)			35.21
Weighted Average Exercise Price Per Share, Ending balance (usd per share)	$ 26.39		$ 26.39