Note 5 - Loans - Credit Quality of Loans (Details) - Loans Collateralizing Asset Backed Securities [Member] - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Recorded investment			$ 1,172,049
Performing Financial Instruments [Member]
Recorded investment			1,170,236
Nonperforming Financial Instruments [Member]
Recorded investment			1,813
Two [Member]
Recorded investment	[1]		1,018,261
Three [Member]
Recorded investment	[1]		132,169
Four [Member]
Recorded investment	[1]		19,806
Five [Member]
Recorded investment	[1]		1,813
Internal Ratings [Member]
Recorded investment	[1]		1,172,049
Baa1 - Baa3 [Member]
Recorded investment			7,300
Ba1 - Ba3 [Member]
Recorded investment			247,686
B1 - B3 [Member]
Recorded investment			856,204
Caa1 - Caa3 [Member]
Recorded investment			59,046
Moody's, Ca Rating [Member]
Recorded investment			1,813
Moodys Credit Rating [Member]
Recorded investment			$ 1,172,049

[1] Loans with an internal rating of 4 or below are reviewed individually to identify loans to be designated for non-accrual status.