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Schedule of Significant Option Groups Outstanding (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Shares | shares	506
Options Exercisable, Shares | shares	256
Options Outstanding, Weighted-Average Exercise Price	$ 19.06
Options Exercisable, Weighted-Average Exercise Price	$ 8.31
$1.48 - $2.58
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	1 year 2 months 23 days
Options Outstanding, Shares | shares	67
Options Exercisable, Shares | shares	67
Range Of Exercise Prices, Lower Limit	$ 1.48
Range Of Exercise Prices, Upper Limit	2.58
Options Outstanding, Weighted-Average Exercise Price	1.83
Options Exercisable, Weighted-Average Exercise Price	$ 1.83
$2.67 - $3.28
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	2 years 2 months 12 days
Options Outstanding, Shares | shares	103
Options Exercisable, Shares | shares	103
Range Of Exercise Prices, Lower Limit	$ 2.67
Range Of Exercise Prices, Upper Limit	3.28
Options Outstanding, Weighted-Average Exercise Price	2.69
Options Exercisable, Weighted-Average Exercise Price	$ 2.69
$7.71 - $19.43
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	3 years 4 months 28 days
Options Outstanding, Shares | shares	166
Options Exercisable, Shares | shares	68
Range Of Exercise Prices, Lower Limit	$ 7.71
Range Of Exercise Prices, Upper Limit	19.43
Options Outstanding, Weighted-Average Exercise Price	18.59
Options Exercisable, Weighted-Average Exercise Price	$ 18.02
$28.56 - $47.70
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	5 years 7 months 13 days
Options Outstanding, Shares | shares	170
Options Exercisable, Shares | shares	18
Range Of Exercise Prices, Lower Limit	$ 28.56
Range Of Exercise Prices, Upper Limit	47.70
Options Outstanding, Weighted-Average Exercise Price	36.30
Options Exercisable, Weighted-Average Exercise Price	$ 28.56

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

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The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

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Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

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Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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