Note 5 - Investments Unrealized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands		Mar. 31, 2018		Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged		$ 28,100
Loaned securities		44,396		$ 27,964
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax				48,778
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax				16,434
Available-for-sale Securities, including Loaned Securities, Amortized Cost Basis				3,617,103
Available-for-sale Securities, including Loaned Securities				3,649,447
US government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged		4,800
Amortized Cost Debt and Equity Securities		65,278		69,667
Available-for-sale Securities		63,656	[1]	69,396
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0		96
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		1,622		367
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Debt and Equity Securities		157,176		156,587
Available-for-sale Securities		159,329		161,722
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		3,882		5,834
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		1,729		699
Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Debt and Equity Securities		1,910,482		1,869,318
Available-for-sale Securities		1,881,117		1,894,886
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		10,525		33,620
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		39,890		8,052
RMBS
Schedule of Available-for-sale Securities [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged		23,300
Amortized Cost Debt and Equity Securities		233,144		189,455
Available-for-sale Securities		228,040	[2]	187,229
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		128		636
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		5,232		2,862
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Debt and Equity Securities		476,601		451,595
Available-for-sale Securities		470,834		453,394
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,085		3,409
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		6,852		1,610
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Debt and Equity Securities		736,967		672,715
Available-for-sale Securities		736,518		674,548
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		1,819		2,655
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		2,268		822
Foreign government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Debt and Equity Securities		32,412		31,417
Available-for-sale Securities		32,396		32,207
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		257		823
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		273		33
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Debt and Equity Securities		3,612,060		3,440,754
Available-for-sale Securities		3,571,890	[3]	3,473,382	[4]
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		17,696		47,073
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		57,866		14,445
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Equity Securities, including Loaned Securities, Amortized Cost Basis	[5]			176,349
Available-for-sale Securities, including Loaned Securities, Equity Securities	[4],[5]			176,065
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	[5]			1,705
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	[5]			1,989
Securities Financing Transaction, Fair Value [Member]
Schedule of Available-for-sale Securities [Line Items]
Loaned securities	[6]	44,396		27,964
Securities Financing Transaction, Fair Value [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Loaned securities		17,200		14,700
Securities Financing Transaction, Fair Value [Member] | Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Loaned securities	[6]	15,508		13,862
Securities Financing Transaction, Fair Value [Member] | Foreign government securities
Schedule of Available-for-sale Securities [Line Items]
Loaned securities	[6]	904		867
Securities Financing Transaction, Fair Value [Member] | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Loaned securities	[6]	$ 27,009		$ 13,235

[1] Includes securities with a fair value of $4.8 million serving as collateral for FHLB advances.

[2] Includes securities with a fair value of $23.3 million serving as collateral for FHLB advances.

[3] Includes $17.2 million of fixed maturity securities loaned to third-party Borrowers under securities lending agreements, classified as other assets in our condensed consolidated balance sheets, as further described below.

[4] Includes $14.7 million of fixed maturity securities and $13.2 million of equity securities loaned to third-party Borrowers under securities lending agreements, classified as other assets in our condensed consolidated balance sheets, as further described below.

[5] Primarily consists of investments in fixed-income and equity exchange-traded funds and publicly-traded business development company equities.

[6] Our securities loaned under securities lending agreements are reported at fair value within other assets in our condensed consolidated balance sheets. All of our securities lending agreements are classified as overnight and revolving. None of the amounts are subject to offsetting.