Note 6 - Investments - Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale Securities, Amortized Cost
Less: loaned securities	$ 135,058	$ 57,499
Fixed-maturities available for sale—at amortized cost	5,391,584	5,393,623
Available-for-sale Securities, Fair Value
Less: loaned securities	135,058	57,499
Fixed-maturity investments available for sale, Total, Fair Value	5,580,212	5,723,340
Fixed-maturities available for sale \| Non asset-backed securities
Available-for-sale Securities, Amortized Cost
Due in one year or less	194,384
Due after one year through five years	1,113,491
Due after five years through ten years	1,222,598
Due after ten years	769,734
Available-for-sale Securities, Fair Value
Due in one year or less	195,823
Due after one year through five years	1,159,751
Due after five years through ten years	1,276,635
Due after ten years	812,301
Fixed-maturities available for sale \| Asset-backed and other Mortgage Backed securities
Available-for-sale Securities, Amortized Cost
Fixed-maturity investments available for sale, Maturity, without Single Maturity Date, Amortized Cost	2,173,618
Available-for-sale Securities, Fair Value
Fixed-maturity investments available for sale, Maturity, without Single Maturity Date, Fair Value	2,221,777
Fixed-maturities available for sale \| Total fixed-maturities available for sale
Available-for-sale Securities, Amortized Cost
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	5,473,825	5,426,787
Fixed-maturities available for sale—at amortized cost	5,391,584	5,393,623
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,666,287	5,759,442
Fixed-maturity investments available for sale, Total, Fair Value	5,580,212	5,723,340
Fixed-maturities available for sale \| Securities Financing Transaction, Cost \| Total fixed-maturities available for sale
Available-for-sale Securities, Amortized Cost
Less: loaned securities	82,241	33,164
Available-for-sale Securities, Fair Value
Less: loaned securities	82,241	33,164
Fixed-maturities available for sale \| Securities Financing Transaction, Fair Value \| Total fixed-maturities available for sale
Available-for-sale Securities, Amortized Cost
Less: loaned securities	86,075	36,102
Available-for-sale Securities, Fair Value
Less: loaned securities	$ 86,075	$ 36,102

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