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Fair Value measurements - Summary of Carrying Values and Associated Fair Values of Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017
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Carrying Value [Member] |  |
Financial assets: |  |
Investments | $ 20,312 | $ 30,053
Level 2 [Member] |  |
Financial assets: |  |
Investments | $ 20,294 | $ 30,038

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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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