Investments - Amortized Cost and Fair Value of Investments With Contractual Maturities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Fixed Maturities Securities Available for Sale, Due in one year or less, Amortized cost	$ 55,635
Fixed Maturities Securities Available for Sale, Due after one year through five years, Amortized cost	233,199
Fixed Maturities Securities Available for Sale, Due after five years through ten years, Amortized cost	41,299
Fixed Maturities Securities Available for Sale, Due after ten years, Amortized cost	56,869
Fixed Maturities Securities Available for Sale, Perpetual Maturity, Amortized Cost	13,727
Fixed Maturities Securities Available for Sale, Amortized cost, Total	611,773
Fixed Maturities Securities Available for Sale, Due in one year or less, Fair Value	55,622
Fixed Maturities Securities Available for Sale, Due after one year through five years, Fair Value	233,244
Fixed Maturities Securities Available for Sale, Due after five years through ten years, Fair Value	41,295
Fixed Maturities Securities Available for Sale, Due after ten years, Fair Value	55,493
Fixed Maturities Securities Available for Sale, Perpetual Maturity, Fair Value	14,487
Fixed Maturities Securities Available for Sale, Fair Value, Total	609,909	$ 589,363
Mortgage-Backed and Asset-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fixed Maturities Securities Available for Sale, Mortgage-backed Securities, Amortized cost	211,044
Fixed Maturities Securities Available for Sale, Mortgage-backed Securities, Fair Value	$ 209,768

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of available-for-sale debt securities at cost, net of adjustments, that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the cost over several maturity groupings. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the fair value over several maturity groupings.

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Amount of available for sale securities with contractual maturities.

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Amount of available-for-sale debt securities at cost, net of adjustments, that do not have a maturity date.

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Amount of available-for-sale debt securities at fair value, that do not have a maturity date.

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