Note 5 - Investments Available for Sale Securities (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 4,804,453			$ 4,804,453				$ 4,549,534
Debt Securities, Available-for-sale, Allowance for Credit Loss	(2,476)			(2,476)
Loaned securities	16,332			16,332				66,442
Fixed-maturities available for sale—at fair value, net of allowance for credit losses of $2,476 as of June 30, 2020 (amortized cost of $4,804,453 and $4,549,534)	5,070,091			5,070,091				4,688,911
Current provision for securities without prior allowance	2,782		$ 0	2,782		$ 0
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, Accumulated Gross Unrealized Gain, before Tax								133
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax								0
Available-for-sale Securities, Debt Securities, Including Loaned Securities								5,224
Total fixed-maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	4,806,448			4,806,448
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,072,210			5,072,210
Securities Financing Transaction, Fair Value | Corporate bonds and notes | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Securities Loaned, Asset, Amortized Cost Basis	1,995			1,995				23,853
Loaned securities	2,119	[1]		2,119	[1]			3,669	[2]
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	122,956			122,956				198,613
Debt Securities, Available-for-sale, Allowance for Credit Loss	0			0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	10,087			10,087				2,048
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0			0				(733)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	133,043			133,043				199,928
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	109,106			109,106				112,003
Debt Securities, Available-for-sale, Allowance for Credit Loss	0			0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	14,102			14,102				8,032
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(91)			(91)				(41)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	123,117			123,117				119,994
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	2,455,572			2,455,572				2,136,819
Debt Securities, Available-for-sale, Allowance for Credit Loss	(2,476)			(2,476)
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	201,051			201,051				106,189
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(3,572)			(3,572)				(1,728)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	2,650,575			2,650,575				2,241,280
Accumulated Allowance for Credit Loss, Available-for-sale Debt Securities	2,476			2,476			$ 0	0
Reduction for securities sold	(306)			(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	798,750			798,750				766,429
Debt Securities, Available-for-sale, Allowance for Credit Loss	0			0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	37,101			37,101				14,452
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(82)			(82)				(1,527)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	835,769			835,769				779,354
Fixed-maturities available for sale | CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Including Loaned Securities	614,556			614,556				593,647
Debt Securities, Available-for-sale, Allowance for Credit Loss	0			0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	31,600			31,600				14,993
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(8,665)			(8,665)				(625)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	637,491			637,491				608,015
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	700,412			700,412				760,785
Debt Securities, Available-for-sale, Allowance for Credit Loss	0			0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,962			1,962				2,018
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(15,499)			(15,499)				(3,674)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	686,875			686,875				759,129
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	5,096			5,096
Debt Securities, Available-for-sale, Allowance for Credit Loss	0			0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	244			244
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0			0
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,340			5,340
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	4,806,448			4,806,448				4,573,387
Debt Securities, Available-for-sale, Amortized Cost	4,804,453			4,804,453				4,549,534
Debt Securities, Available-for-sale, Allowance for Credit Loss	(2,476)			(2,476)
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	296,147			296,147				147,865
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(27,909)			(27,909)				(8,328)
Available-for-sale Securities, Debt Securities, Including Loaned Securities	5,072,210			5,072,210				4,712,924
Fixed-maturities available for sale—at fair value, net of allowance for credit losses of $2,476 as of June 30, 2020 (amortized cost of $4,804,453 and $4,549,534)	$ 5,070,091			$ 5,070,091				4,688,911
Fixed-maturities available for sale | Securities Financing Transaction, Fair Value | Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Loaned securities								$ 24,013

[1] Securities loaned to third-party borrowers under securities lending agreements are classified as other assets in our condensed consolidated balance sheets. See Note 5 for more information.

[2] Securities loaned to third-party borrowers under securities lending agreements are classified as other assets in our condensed consolidated balance sheets. See Note 5 for more information.