Note 6 - Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 57,499	$ 66,442
Fixed-maturities available for sale—amortized cost	5,393,623	4,549,534
Fixed-maturities available for sale—at fair value	5,723,340	4,688,911
Allowance for Credit Losses	(948)
Fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Allowance for Credit Losses	(948)
Fixed-maturities available for sale \| US government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	176,033	198,613
Available-for-sale Securities, Debt Securities, Including Loaned Securities	174,099	199,928
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,677	2,048
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(3,611)	(733)
Fixed-maturities available for sale \| State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	149,258	112,003
Available-for-sale Securities, Debt Securities, Including Loaned Securities	165,271	119,994
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	16,113	8,032
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(100)	(41)
Allowance for Credit Losses	0
Fixed-maturities available for sale \| Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	2,832,350	2,136,819
Available-for-sale Securities, Debt Securities, Including Loaned Securities	3,078,415	2,241,280
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	250,771	106,189
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(3,758)	(1,728)
Allowance for Credit Losses	948	0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Not Previously Recorded	1,254
Debt Securities, Available-for-sale, Allowance for Credit Loss, Recovery	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	(306)
Fixed-maturities available for sale \| RMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	799,814	766,429
Available-for-sale Securities, Debt Securities, Including Loaned Securities	833,939	779,354
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	34,439	14,452
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(314)	(1,527)
Allowance for Credit Losses	0
Fixed-maturities available for sale \| CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	645,071	574,037
Available-for-sale Securities, Debt Securities, Including Loaned Securities	681,265	588,420
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	39,495	14,993
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(3,301)	(610)
Allowance for Credit Losses	0
Fixed-maturities available for sale \| Other ABS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	249,988	314,946
Available-for-sale Securities, Debt Securities, Including Loaned Securities	252,457	316,163
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,901	1,789
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(432)	(572)
Allowance for Credit Losses	0
Fixed-maturities available for sale \| Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	5,100	5,091
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,438	5,224
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	338	133
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Allowance for Credit Losses	0
Fixed-maturities available for sale \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	5,426,787	4,573,387
Fixed-maturities available for sale—amortized cost	5,393,623	4,549,534
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,759,442	4,712,924
Fixed-maturities available for sale—at fair value	5,723,340	4,688,911
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	347,760	147,865
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(14,157)	(8,328)
Allowance for Credit Losses	948
Fixed-maturities available for sale \| US Government Corporations and Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Allowance for Credit Losses	0
Fixed-maturities available for sale \| CLO
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	569,173	465,449
Available-for-sale Securities, Debt Securities, Including Loaned Securities	568,558	462,561
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,026	229
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(2,641)	(3,117)
Allowance for Credit Losses	0
Fixed-maturities available for sale \| Securities Financing Transaction, Amortized Cost \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	33,164	23,853
Fixed-maturities available for sale \| Securities Financing Transaction, Fair Value
Debt Securities, Available-for-sale [Line Items]
Loaned securities	36,100
Fixed-maturities available for sale \| Securities Financing Transaction, Fair Value \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 36,102	$ 24,013

Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities

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Available-for-sale Securities, Debt Securities, Including Loaned Securities

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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).

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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded.

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Amount of increase in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), from recovery.

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This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.

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Amount of asset associated with securities loaned to entities in exchange for collateral.

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