Note 5 - Investments Schedule of Contractual Maturities (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged		$ 122,800
Available-for-sale Securities, Amortized Cost
Available-for-sale Debt Securities, Amortized Cost Basis		3,659,311	$ 3,426,217
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Securities		3,586,055	3,458,719
FHLB advances		115,308	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held		0	0
Debt Securities
Available-for-sale Securities, Amortized Cost
Available-for-sale Debt Securities, Amortized Cost Basis	[1]	3,675,725
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Securities	[1]	3,602,052
Assets Held by Insurance Regulators		15,400	$ 11,800
Non Asset Backed Security Investments, Contractual Maturities
Available-for-sale Securities, Amortized Cost
Due in one year or less	[2]	45,836
Due after one year through five years	[2]	789,095
Due after five years through ten years	[2]	1,012,314
Due after ten years	[2]	396,485
Available-for-sale Securities, Fair Value
Due in one year or less	[2]	45,694
Due after one year through five years	[2]	774,712
Due after five years through ten years	[2]	973,838
Due after ten years	[2]	393,834
RMBS
Available-for-sale Securities, Amortized Cost
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	[3]	249,577
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	[3]	243,659
CMBS
Available-for-sale Securities, Amortized Cost
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	[3]	487,805
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	[3]	477,751
Other ABS
Available-for-sale Securities, Amortized Cost
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	[3]	694,613
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	[3]	$ 692,564

[1] Includes securities loaned under securities lending agreements.

[2] Actual maturities may differ as a result of calls before scheduled maturity.

[3] RMBS, CMBS and Other ABS are shown separately, as they are not due at a single maturity date.