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Schedule of Weighted-Average Information by Range of Exercise Prices for Stock Options Outstanding and Exercisable (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding at December 31, 2017 | shares	2,263,126
Options Exercisable at December 31, 2017 | shares	1,387,259
$4.75 to $11.50
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, minimum	$ 4.75
Range of Exercise Prices, maximum	$ 11.50
Options Outstanding at December 31, 2017 | shares	414,134
Options Outstanding, Weighted-Average Exercise Price	$ 9.56
Weighted Average Remaining Contractual Life, in Years	4 years
Options Exercisable at December 31, 2017 | shares	414,134
Options Exercisable, Weighted-Average Exercise Price	$ 9.56
$17.46 to $25.34
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, minimum	17.46
Range of Exercise Prices, maximum	$ 25.34
Options Outstanding at December 31, 2017 | shares	556,847
Options Outstanding, Weighted-Average Exercise Price	$ 20.58
Weighted Average Remaining Contractual Life, in Years	7 years
Options Exercisable at December 31, 2017 | shares	556,847
Options Exercisable, Weighted-Average Exercise Price	$ 20.58
$26.47 to $50.16
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, minimum	26.47
Range of Exercise Prices, maximum	$ 50.16
Options Outstanding at December 31, 2017 | shares	1,292,145
Options Outstanding, Weighted-Average Exercise Price	$ 36.63
Weighted Average Remaining Contractual Life, in Years	8 years
Options Exercisable at December 31, 2017 | shares	416,278
Options Exercisable, Weighted-Average Exercise Price	$ 31.20

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The ceiling 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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