Summary of Investments - Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available-For-Sale, Amortized Cost
Due in one year or less	$ 55,041
Due after one year through five years	469,238
Due after five years through 10 years	353,810
Due after 10 years	455,832
Available-For-Sale, Fair Value
Due in one year or less	55,699
Due after one year through five years	492,892
Due after five years through 10 years	373,415
Due after 10 years	481,679
Fair Value	1,727,601	$ 1,825,438
Asset-backed securities
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	322
Amortized Cost	322	314
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	908
Fair Value	908	926
Mortgage-backed securities
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	22,251
Amortized Cost	22,251	20,305
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	22,373
Fair Value	22,373	$ 20,577
Collateralized mortgage obligations
Available-For-Sale, Amortized Cost
Securities not categorized by contractual maturity	298,734
Available-For-Sale, Fair Value
Securities not categorized by contractual maturity	300,635
Fixed maturities
Available-For-Sale, Amortized Cost
Amortized Cost	1,655,228
Available-For-Sale, Fair Value
Fair Value	$ 1,727,601

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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