Note 6 - Investments - Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Available-for-sale Securities, Amortized Cost
Less: loaned securities	$ 130,850	$ 57,499
Fixed-maturities available for sale—at amortized cost	5,349,405	5,393,623
Available-for-sale Securities, Fair Value
Less: loaned securities	130,850	57,499
Fixed-maturity investments available for sale, Total, Fair Value	5,572,813	5,723,340
Fixed-maturities available for sale \| Non asset-backed securities
Available-for-sale Securities, Amortized Cost
Due in one year or less	187,546
Due after one year through five years	1,130,214
Due after five years through ten years	1,242,012
Due after ten years	710,171
Available-for-sale Securities, Fair Value
Due in one year or less	189,292
Due after one year through five years	1,182,709
Due after five years through ten years	1,308,582
Due after ten years	762,433
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	2,177,564
Available-for-sale Securities, Fair Value
Fixed-maturity investments available for sale, Maturity, without Single Maturity Date, Fair Value	2,230,665
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	5,447,507	5,426,787
Fixed-maturities available for sale—at amortized cost	5,349,405	5,393,623
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,673,681	5,759,442
Fixed-maturity investments available for sale, Total, Fair Value	5,572,813	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	98,102	33,164
Available-for-sale Securities, Fair Value
Less: loaned securities	98,102	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	100,868	36,102
Available-for-sale Securities, Fair Value
Less: loaned securities	$ 100,868	$ 36,102

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