Investments - Summarized Fair Value and Gross Unrealized Losses on Available-for-sale Debt Securities (Detail) $ in Thousands	Sep. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Number of issues \| security	60	331
Less than 12 months, Fair value	$ 59,989	$ 279,093
Less than 12 months, Unrealized losses	$ (304)	$ (4,063)
12 months or longer, Number of issues \| security	75	281
12 months or longer, Fair value	$ 117,606	$ 337,226
12 months or longer, Unrealized losses	$ (696)	$ (8,548)
Fixed Maturities [Member] \| U.S. Government Obligations and Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Number of issues \| security	2	0
Less than 12 months, Fair value	$ 3,907	$ 0
Less than 12 months, Unrealized losses	$ (38)	$ 0
12 months or longer, Number of issues \| security	6	13
12 months or longer, Fair value	$ 41,419	$ 56,531
12 months or longer, Unrealized losses	$ (168)	$ (1,039)
Fixed Maturities [Member] \| Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Number of issues \| security	24	228
Less than 12 months, Fair value	$ 24,357	$ 210,152
Less than 12 months, Unrealized losses	$ (115)	$ (3,318)
12 months or longer, Number of issues \| security	22	160
12 months or longer, Fair value	$ 19,923	$ 131,225
12 months or longer, Unrealized losses	$ (83)	$ (3,418)
Fixed Maturities [Member] \| Mortgage-Backed and Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Number of issues \| security	26	36
Less than 12 months, Fair value	$ 30,609	$ 57,487
Less than 12 months, Unrealized losses	$ (139)	$ (196)
12 months or longer, Number of issues \| security	38	103
12 months or longer, Fair value	$ 53,895	$ 148,436
12 months or longer, Unrealized losses	$ (370)	$ (3,959)
Fixed Maturities [Member] \| Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Number of issues \| security	0	6
Less than 12 months, Fair value	$ 0	$ 3,362
Less than 12 months, Unrealized losses	$ 0	$ (43)
12 months or longer, Number of issues \| security	1	0
12 months or longer, Fair value	$ 275	$ 0
12 months or longer, Unrealized losses	$ (5)	$ 0
Fixed Maturities [Member] \| Redeemable Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Number of issues \| security	8	61
Less than 12 months, Fair value	$ 1,116	$ 8,092
Less than 12 months, Unrealized losses	$ (12)	$ (506)
12 months or longer, Number of issues \| security	8	5
12 months or longer, Fair value	$ 2,094	$ 1,034
12 months or longer, Unrealized losses	$ (70)	$ (132)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Publisher FASB
-Name Accounting Standards Codification
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

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-Publisher FASB
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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