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Insurance Activity - Components of Liability for Losses and Loss Adjustment Reserves (Detail) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Effects of Reinsurance [Line Items] |  |  |  |
Total losses and loss adjustment reserves | $ 408 | $ 474 | [1] | $ 811
Case-basis reserves [Member] |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Total losses and loss adjustment reserves | 12 | 151 |  |
IBNR reserves [Member] |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Total losses and loss adjustment reserves | 1 | 1 |  |
Premium deficiency reserves [Member] |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Total losses and loss adjustment reserves | $ 395 | $ 322 |  |
[1] | Balances derived from audited financial statements as of December 31, 2017.

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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
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