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Changes in Liability for Unrecognized Gross Tax Benefits (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Tax Contingency [Line Items] |  |  |
Uncertain tax positions at beginning of year | $ 33,487 | $ 30,456 | $ 24,779
Additions for tax positions relating to current-year operations | 4,332 | 1,304 | 3,827
Additions for tax positions relating to prior tax years | 1,398 | 1,997 | 2,935
Subtractions for tax positions relating to prior tax years | (5,101) | (270) | (963)
Reductions in balance due to settlements | (435) |  | (122)
Uncertain tax positions at end of year | $ 33,681 | $ 33,487 | $ 30,456

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- Definition Amount of increase decrease in unrecognized tax benefits resulting from settlements with taxing authorities. + References No definition available. + Details
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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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