Note 5 - Investments Unrealized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 2,487,445	$ 1,893,356
Available-for-sale Securities	2,523,835	1,940,891
Available-for-sale Equity Securities, Amortized Cost Basis	500	75,538
Available-for-sale Securities, Equity Securities	500	75,430
Amortized Cost Debt and Equity Securities	2,487,945	1,968,894
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	50,650	6,297
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	14,760	34,300
US government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	152,233	13,773
Available-for-sale Securities	153,303	13,752
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	1,072	0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	2	21
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	72,249	36,920
Available-for-sale Securities	75,289	37,900
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	3,160	1,100
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	120	120
Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,027,955	815,024
Available-for-sale Securities	1,056,504	802,193
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	34,065	4,460
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	5,516	17,291
RMBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	304,401	226,744
Available-for-sale Securities	307,516	224,905
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	3,227	625
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	112	2,464
CMBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	504,978	415,780
Available-for-sale Securities	509,070	406,910
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	7,926	69
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	3,834	8,939
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	399,936	359,452
Available-for-sale Securities	396,461	355,494
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	968	16
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	4,443	3,974
Foreign government securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	25,693	25,663
Available-for-sale Securities	25,192	24,307
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	232	27
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	733	1,383
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,487,445	1,893,356
Available-for-sale Securities	2,523,335	1,865,461
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	50,650	6,297
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	14,760	34,192
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	500	75,538	[1]
Available-for-sale Securities, Equity Securities	500	75,430	[1]
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	0	0	[1]
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0	$ 108	[1]

[1] Comprising primarily a multi-sector exchange-traded fund.