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Summary Selected Quarterly Financial Data - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017
Research Services [Member] |  |  |
Quantifying Misstatement In Current Year Financial Statements [Line Items] |  |  |
Out-of-period correction revenue | $ 1.0 |  |
Out-of-period correction revenue, after tax | $ 0.7 |  |
Understatement of Revenue from Reprint Product Line [Member] |  |  |
Quantifying Misstatement In Current Year Financial Statements [Line Items] |  |  |
Out-of-period correction revenue |  | $ 0.8 | $ 0.2
Out-of-period correction revenue, after tax |  | $ 0.5 | $ 0.1

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- Definition Amount of each individual error being corrected in the correcting adjustment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 1.N) -URI http://asc.fasb.org/extlink&oid=112272810&loc=d3e30840-122693 + Details
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