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Investments - A Summary of the Company's Realized Gains and Losses on Sales, Calls or Redemptions of Investments (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
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Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales |  |  |  |  |  |  |  |  | $ 4,432 | $ 10,548 | $ 10,990
Gross realized investment gains |  |  |  |  |  |  |  |  | 177 | 750 | 1,354
Gross realized investment (losses) |  |  |  |  |  |  |  |  | (162) | (451) | (471)
Net realized investment gains |  |  |  |  |  |  |  |  | 15 | 299 | 883
Impairments |  |  |  |  |  |  |  |  | (2,653) | (222) | (2,229)
Other, including gains on calls and redemptions |  |  |  |  |  |  |  |  | 144 | 620 | 135
Net realized gains (losses) on investments | $ 24 | $ 40 | $ (2,617) | $ 59 | $ 516 | $ (152) | $ 232 | $ 101 | (2,494) | 697 | (1,211)
Fixed Maturity Securities Available for Sale [Member] |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales |  |  |  |  |  |  |  |  | 4,432 | 768 | 2,090
Gross realized investment gains |  |  |  |  |  |  |  |  | 177 | 1 | 90
Gross realized investment (losses) |  |  |  |  |  |  |  |  | (162) |  |
Net realized investment gains |  |  |  |  |  |  |  |  | 15 | 1 | 90
Impairments |  |  |  |  |  |  |  |  | (2,653) | (222) |
Other, including gains on calls and redemptions |  |  |  |  |  |  |  |  | 102 | 244 | 38
Net realized gains (losses) on investments |  |  |  |  |  |  |  |  | (2,536) | 23 | 128
Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales |  |  |  |  |  |  |  |  |  | 9,780 | 8,900
Gross realized investment gains |  |  |  |  |  |  |  |  |  | 749 | 1,264
Gross realized investment (losses) |  |  |  |  |  |  |  |  |  | (451) | (471)
Net realized investment gains |  |  |  |  |  |  |  |  |  | 298 | 793
Impairments |  |  |  |  |  |  |  |  |  |  | (2,229)
Net realized gains (losses) on investments |  |  |  |  |  |  |  |  |  | 298 | (1,436)
Other [Member] |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Other, including gains on calls and redemptions |  |  |  |  |  |  |  |  | 42 | 376 | 97
Net realized gains (losses) on investments |  |  |  |  |  |  |  |  | $ 42 | $ 376 | $ 97

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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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