Fair Value Measurements - Summary of Carrying Values and Corresponding Fair Values for Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	$ 619,400	$ 629,668
Fixed maturity securities-held-to-maturity	620,936	639,309
Fixed maturity securities-available-for-sale	459,264	465,594
Equity securities	11,425	9,282
Short-term investments	44,704	25,770
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	620,936	639,309
Fixed maturity securities-available-for-sale	459,264	465,594
Equity securities	11,425	9,282
Short-term investments	44,704	25,770
Cash and cash equivalents	36,072	55,559
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-available-for-sale	459,264	465,594
Equity securities	11,425	9,282
Short-term investments	44,704	25,770
Cash and cash equivalents	$ 36,072	$ 55,559

Amount of debt securities categorized neither as held-to-maturity nor trading.

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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Fair value portion 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.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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