Note 7 - Asset-backed Securities Issued - Asset-backed Securities Issued - CLO III, CLO IV, and CLO V (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Mar. 31, 2019
Notes Originally Issued		$ 86,000
Less: Debt issuance costs	$ (2,428)	$ (2,325)
Total asset-backed securities issued	1,112,342
Unsecured Subordinated Notes [Member]
Notes Originally Issued	$ 7,221
Weighted average remaining maturity (Year)	11 years
Unsecured Subordinated Notes [Member] \| Minimum [Member]
Interest Rate Spread to LIBOR	6.90%
Unsecured Subordinated Notes [Member] \| Maximum [Member]
Interest Rate Spread to LIBOR	11.00%
CLO III, CLO IV, and CLOV [Member]
Notes Originally Issued	$ 1,114,100
Less: Debt issuance costs	(8,979)
CLO III, CLO IV, and CLOV [Member] \| Class A Senior Secured [Member]
Notes Originally Issued	$ 769,750
CLO III, CLO IV, and CLOV [Member] \| Class A Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Weighted average remaining maturity (Year)	10 years 14 days
CLO III, CLO IV, and CLOV [Member] \| Class A Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Interest Rate Spread to LIBOR	0.85%
CLO III, CLO IV, and CLOV [Member] \| Class A Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member]
Interest Rate Spread to LIBOR	1.37%
CLO III, CLO IV, and CLOV [Member] \| Class B Senior Secured [Member]
Notes Originally Issued	$ 143,700
CLO III, CLO IV, and CLOV [Member] \| Class B Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Weighted average remaining maturity (Year)	10 years 14 days
CLO III, CLO IV, and CLOV [Member] \| Class B Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Interest Rate Spread to LIBOR	1.30%
CLO III, CLO IV, and CLOV [Member] \| Class B Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member]
Interest Rate Spread to LIBOR	1.90%
CLO III, CLO IV, and CLOV [Member] \| Class C Senior Secured [Member]
Notes Originally Issued	$ 71,500
CLO III, CLO IV, and CLOV [Member] \| Class C Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Weighted average remaining maturity (Year)	9 years 361 days
CLO III, CLO IV, and CLOV [Member] \| Class C Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Interest Rate Spread to LIBOR	1.80%
CLO III, CLO IV, and CLOV [Member] \| Class C Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member]
Interest Rate Spread to LIBOR	2.65%
CLO III, CLO IV, and CLOV [Member] \| Class D Senior Secured [Member]
Notes Originally Issued	$ 68,350
CLO III, CLO IV, and CLOV [Member] \| Class D Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Weighted average remaining maturity (Year)	10 years 3 days
CLO III, CLO IV, and CLOV [Member] \| Class D Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Interest Rate Spread to LIBOR	2.60%
CLO III, CLO IV, and CLOV [Member] \| Class D Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member]
Interest Rate Spread to LIBOR	4.15%
CLO III, CLO IV, and CLOV [Member] \| Class E Senior Secured [Member]
Notes Originally Issued	$ 60,800
CLO III, CLO IV, and CLOV [Member] \| Class E Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Weighted average remaining maturity (Year)	10 years 10 days
CLO III, CLO IV, and CLOV [Member] \| Class E Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Interest Rate Spread to LIBOR	5.70%
CLO III, CLO IV, and CLOV [Member] \| Class E Senior Secured [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member]
Interest Rate Spread to LIBOR	6.80%

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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