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Interim Consolidated Financial Statements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Summary Of Significant Accounting Policy [Line Items]
Tax withholding in financing activities		$ 2,511	$ 2,069
ASU No. 2016-09 [Member]
Summary Of Significant Accounting Policy [Line Items]
Cumulative effect adjustment to increase or (reduce) retained earnings				$ 200
Tax benefit recognized	$ 300	300
Tax withholding in financing activities		$ 2,500
Change in reclassification of tax withholding			$ 2,400
Early Adoption of ASU No. 2016-16 [Member]
Summary Of Significant Accounting Policy [Line Items]
Cumulative effect adjustment to increase or (reduce) retained earnings				$ (500)

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Summary Of Significant Accounting Policy [Line Items]

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Amount of the cumulative effect on retained earnings net of related income tax effect.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 25
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-URI http://asc.fasb.org/extlink&oid=96949009&loc=SL79513924-113897

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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