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Summary of Significant Accounting Policies - Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands | Sep. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Dec. 31, 2016
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Cash and Cash Equivalents [Line Items] |  |  |  |  |  |
Cash and cash equivalents | $ 113,524 | $ 120,357 | $ 138,285 | $ 91,532 | $ 99,565 | $ 112,183
Cash equivalents | 55,200 |  | 7,100 |  |  |
Domestic Bank Accounts |  |  |  |  |  |
Cash and Cash Equivalents [Line Items] |  |  |  |  |  |
Cash and cash equivalents | 79,300 |  | 83,100 |  |  |
Foreign Bank Accounts |  |  |  |  |  |
Cash and Cash Equivalents [Line Items] |  |  |  |  |  |
Cash and cash equivalents | 34,200 |  | 55,200 |  |  |
Investments in Joint Ventures |  |  |  |  |  |
Cash and Cash Equivalents [Line Items] |  |  |  |  |  |
Cash and cash equivalents | 12,400 |  | 16,700 |  |  |
Domestic Joint Ventures |  |  |  |  |  |
Cash and Cash Equivalents [Line Items] |  |  |  |  |  |
Cash and cash equivalents | $ 11,900 |  | $ 10,000 |  |  |

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- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3044-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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