Note 5 - Investments Available for Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 65,444	$ 27,860
Debt Securities, Available-for-sale, Amortized Cost	4,369,273	4,098,962
Debt Securities, Available-for-sale	4,527,223	4,021,575
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	4,403,293
Available-for-sale Securities, Debt Securities, Including Loaned Securities	4,561,841
Fixed maturities \| US government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	176,682	85,532
Available-for-sale Securities, Debt Securities, Including Loaned Securities	182,415	84,070
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	5,839	46
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	106	1,508
Fixed maturities \| State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	100,070	138,022
Available-for-sale Securities, Debt Securities, Including Loaned Securities	110,981	138,313
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	10,911	2,191
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	1,900
Fixed maturities \| Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	2,254,627	2,288,720
Available-for-sale Securities, Debt Securities, Including Loaned Securities	2,362,004	2,229,885
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	108,541	5,053
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,164	63,888
Fixed maturities \| RMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	605,687	334,843
Available-for-sale Securities, Debt Securities, Including Loaned Securities	619,935	332,142
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	15,286	1,785
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,038	4,486
Fixed maturities \| CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	542,284	546,729
Available-for-sale Securities, Debt Securities, Including Loaned Securities	563,338	539,915
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	21,966	544
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	912	7,358
Fixed maturities \| Other ABS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	718,854	712,748
Available-for-sale Securities, Debt Securities, Including Loaned Securities	717,986	704,662
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,394	814
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3,262	8,900
Fixed maturities \| Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	5,089
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,182
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	93
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0
Fixed maturities \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	4,403,293	4,106,594
Debt Securities, Available-for-sale, Amortized Cost	4,369,273	4,098,962
Available-for-sale Securities, Debt Securities, Including Loaned Securities	4,561,841	4,028,987
Debt Securities, Available-for-sale	4,527,223	4,021,575
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	165,030	10,433
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6,482	88,040
Fixed maturities \| Securities Financing Transaction, Cost \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	34,020	7,632
Fixed maturities \| Securities Financing Transaction, Fair Value \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Loaned securities	$ 34,618	$ 7,412

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