Note 6 - Investments Available for Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 66,442	$ 27,860
Fixed-maturities available for sale—amortized cost	4,549,534	4,098,962
Fixed-maturities available for sale—at fair value	4,688,911	4,021,575
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	198,613	85,532
Available-for-sale Securities, Debt Securities, Including Loaned Securities	199,928	84,070
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,048	46
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	733	1,508
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	112,003	138,022
Available-for-sale Securities, Debt Securities, Including Loaned Securities	119,994	138,313
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	8,032	2,191
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	41	1,900
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	2,136,819	2,288,720
Available-for-sale Securities, Debt Securities, Including Loaned Securities	2,241,280	2,229,885
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	106,189	5,053
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,728	63,888
Fixed-maturities available for sale \| RMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	766,429	334,843
Available-for-sale Securities, Debt Securities, Including Loaned Securities	779,354	332,142
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	14,452	1,785
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,527	4,486
Fixed-maturities available for sale \| CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	593,647	546,729
Available-for-sale Securities, Debt Securities, Including Loaned Securities	608,015	539,915
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	14,993	544
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	625	7,358
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	760,785	712,748
Available-for-sale Securities, Debt Securities, Including Loaned Securities	759,129	704,662
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,018	814
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3,674	8,900
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	5,091
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,224
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	133
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	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	4,573,387	4,106,594
Fixed-maturities available for sale—amortized cost	4,549,534	4,098,962
Available-for-sale Securities, Debt Securities, Including Loaned Securities	4,712,924	4,028,987
Fixed-maturities available for sale—at fair value	4,688,911	4,021,575
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	147,865	10,433
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	8,328	88,040
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	23,853	7,632
Fixed-maturities available for sale \| Securities Financing Transaction, Fair Value
Debt Securities, Available-for-sale [Line Items]
Loaned securities	24,000
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	$ 24,013	$ 7,412

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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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