Note 6 - Investments - Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Available-for-sale Securities, Amortized Cost
Less: loaned securities	$ 134,304	$ 57,499
Fixed-maturities available for sale—at amortized cost	5,404,119	5,393,623
Available-for-sale Securities, Fair Value
Less: loaned securities	134,304	57,499
Fixed-maturity investments available for sale, Total, Fair Value	5,553,711	5,723,340
Fixed-maturities available for sale \| Non asset-backed securities
Available-for-sale Securities, Amortized Cost
Due in one year or less	132,399
Due after one year through five years	1,154,711
Due after five years through ten years	1,232,690
Due after ten years	747,779
Available-for-sale Securities, Fair Value
Due in one year or less	133,403
Due after one year through five years	1,203,984
Due after five years through ten years	1,278,861
Due after ten years	750,351
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	2,235,500
Available-for-sale Securities, Fair Value
Fixed-maturity investments available for sale, Maturity, without Single Maturity Date, Fair Value	2,283,382
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	5,503,079	5,426,787
Fixed-maturities available for sale—at amortized cost	5,404,119	5,393,623
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,649,981	5,759,442
Fixed-maturity investments available for sale, Total, Fair Value	5,553,711	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	98,960	33,164
Available-for-sale Securities, Fair Value
Less: loaned securities	98,960	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	96,270	36,102
Available-for-sale Securities, Fair Value
Less: loaned securities	$ 96,270	$ 36,102

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