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Financial Instruments - Summary of Bond Activity (Detail) - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended
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Jun. 30, 2018 | Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract] |  |
Fair value at beginning of period | $ 51,101 | $ 44,573
Purchases | 10,345 | 15,546
Redemptions | (1,098) | (940)
Maturities | (6,175) | (7,845)
Decrease in bond premium | (48) | (160)
Fair market value adjustment | (451) | (73)
Fair value at end of period | $ 53,674 | $ 51,101

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- Definition Financial instruments owned corporate debt maturities. + References No definition available. + Details
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- Definition Financial instrument purchases of corporate and municipal debt. + References No definition available. + Details
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- Definition Financial instruments owned corporate debt redemptions. + References No definition available. + Details
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- Definition Increase (Decrease) in bond premium. + References No definition available. + Details
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- References No definition available. + Details
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- Definition Fair value of firm holdings in corporate fixed income securities. Includes pledged and unpledged holdings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
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