Note 6 - Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 5,404,119	$ 5,393,623
Debt Securities, Available-for-sale, Allowance for Credit Loss	(638)	(948)
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 \| U.S. government and agencies securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	172,927	176,033
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	323	1,677
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(8,681)	(3,611)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	164,569	174,099
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	151,222	149,258
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	11,326	16,113
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(1,510)	(100)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	161,038	165,271
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	2,938,328	2,832,350
Debt Securities, Available-for-sale, Allowance for Credit Loss	(638)	(948)	$ 0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	145,509	250,771
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(47,600)	(3,758)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	3,035,599	3,078,415
Fixed-maturities available for sale \| RMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	752,109	799,814
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	25,667	34,439
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(3,666)	(314)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	774,110	833,939
Fixed-maturities available for sale \| CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	685,914	645,071
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	27,763	39,495
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(5,330)	(3,301)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	708,347	681,265
Fixed-maturities available for sale \| CLO
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	561,013	569,173
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,183	2,026
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(608)	(2,641)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	562,588	568,558
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	236,464	249,988
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,334	2,901
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(461)	(432)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	238,337	252,457
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	5,102	5,100
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	291	338
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,393	5,438
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	5,503,079	5,426,787
Debt Securities, Available-for-sale, Amortized Cost	5,404,119	5,393,623
Debt Securities, Available-for-sale, Allowance for Credit Loss	(638)	(948)
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	215,396	347,760
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(67,856)	(14,157)
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
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	98,960	33,164
Fixed-maturities available for sale \| Securities Financing Transaction, Fair Value \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Less: loaned securities	$ 96,270	$ 36,102

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

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