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Financial Instruments - Summary of Bond Activity (Detail) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
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Sep. 30, 2018 | Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract] |  |
Fair value at beginning of period | $ 51,101 | $ 44,573
Purchases | 10,745 | 15,546
Redemptions | (1,331) | (940)
Maturities | (7,370) | (7,845)
Decrease in bond premium | (219) | (160)
Fair market value adjustment | (538) | (73)
Fair value at end of period | $ 52,388 | $ 51,101

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- Definition Fair market value adjustment of bonds. + References No definition available. + Details
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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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