Note 5 - Investments Schedule of Contractual Maturities (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
Available-for-sale Securities, Amortized Cost
Available-for-sale Debt Securities, Amortized Cost Basis		3,594,591	$ 3,426,217
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Securities		3,554,734	3,458,719
FHLB advances		25,550	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]	3,612,060
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Securities	[1]	3,571,890
Assets Held by Insurance Regulators		14,900	$ 11,800
Non Asset Backed Security Investments, Contractual Maturities
Available-for-sale Securities, Amortized Cost
Due in one year or less	[2]	35,241
Due after one year through five years	[2]	745,894
Due after five years through ten years	[2]	1,016,043
Due after ten years	[2]	368,170
Available-for-sale Securities, Fair Value
Due in one year or less	[2]	35,146
Due after one year through five years	[2]	735,622
Due after five years through ten years	[2]	989,756
Due after ten years	[2]	375,974
RMBS
Available-for-sale Securities, Amortized Cost
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	[3]	233,144
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	[3]	228,040
CMBS
Available-for-sale Securities, Amortized Cost
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	[3]	476,601
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	[3]	470,834
Other ABS
Available-for-sale Securities, Amortized Cost
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	[3]	736,967
Available-for-sale Securities, Fair Value
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	[3]	$ 736,518

[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.