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Summary of Significant Accounting Policies - Income Taxes (Detail) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Income Tax Examination [Line Items] |  |  |  |
Total amount of unrecognized tax benefits relating to uncertain tax positions | $ 36,229 | $ 35,240 | $ 54,541 | $ 50,668
Amount of unrecognized tax benefits increase | 1,000 |  |  |
Unrecognized tax benefits, increase from current period tax positions | 7,040 | 4,227 | 5,340 |
Unrecognized tax benefits, increase from prior year tax positions | 2,200 |  |  |
Unrecognized tax benefits, decrease resulting from expiration of statute of limitations | 8,252 | 23,448 | 282 |
Maximum |  |  |  |
Income Tax Examination [Line Items] |  |  |  |
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months | $ 13,655 | $ 12,332 | $ 27,485 |

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- Definition Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d)(3) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + 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 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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