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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax Contingency [Line Items] |  |  |
Uncertain tax positions at beginning of year | $ 33,681 | $ 33,487 | $ 30,456
Additions for tax positions relating to current-year operations | 0 | 4,332 | 1,304
Additions for tax positions relating to prior tax years | 1,660 | 1,398 | 1,997
Subtractions for tax positions relating to prior tax years | (1,984) | (5,101) | (270)
Reductions in balance due to settlements | 0 | (435) | 0
Uncertain tax positions at end of year | $ 33,357 | $ 33,681 | $ 33,487

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 10B -URI http://asc.fasb.org/extlink&oid=84176650&loc=SL37586934-109318 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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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