Note 5 - Investments Available for Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 4,564,616	$ 4,549,534
Loaned securities	47,520	66,442
Debt Securities, Available-for-sale	4,603,613	4,688,911
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
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	4,569,995
Available-for-sale Securities, Debt Securities, Including Loaned Securities	4,607,397
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	148,382	198,613
Available-for-sale Securities, Debt Securities, Including Loaned Securities	159,240	199,928
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	10,858	2,048
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	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	111,831	112,003
Available-for-sale Securities, Debt Securities, Including Loaned Securities	116,975	119,994
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	5,462	8,032
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	318	41
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	2,239,543	2,136,819
Available-for-sale Securities, Debt Securities, Including Loaned Securities	2,268,850	2,241,280
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	77,884	106,189
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	48,577	1,728
Fixed-maturities available for sale \| RMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	747,271	766,429
Available-for-sale Securities, Debt Securities, Including Loaned Securities	779,590	779,354
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	33,122	14,452
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	803	1,527
Fixed-maturities available for sale \| CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	609,518	593,647
Available-for-sale Securities, Debt Securities, Including Loaned Securities	610,877	608,015
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	13,356	14,993
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	11,997	625
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	708,357	760,785
Available-for-sale Securities, Debt Securities, Including Loaned Securities	666,918	759,129
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,251	2,018
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	42,690	3,674
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	5,093
Available-for-sale Securities, Debt Securities, Including Loaned Securities	4,947
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	146
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	4,569,995	4,573,387
Debt Securities, Available-for-sale, Amortized Cost	4,564,616	4,549,534
Available-for-sale Securities, Debt Securities, Including Loaned Securities	4,607,397	4,712,924
Debt Securities, Available-for-sale	4,603,613	4,688,911
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	141,933	147,865
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	104,531	8,328
Fixed-maturities available for sale \| Securities Financing Transaction, Cost \| Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Securities Loaned, Asset, Amortized Cost Basis	5,379	23,853
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	$ 3,784	$ 24,013

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