Note 2 - Significant Accounting Policies and Consolidated Financial Statement Components (Details Textual) $ in Thousands	1 Months Ended									3 Months Ended			9 Months Ended		12 Months Ended
	Nov. 13, 2020 USD ($)	Oct. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)	Nov. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Nov. 30, 2018 USD ($)	Jul. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Payments to Acquire Loans and Leases Held-for-investment, Total										$ 47,100	$ 45,400		$ 139,700	$ 138,600
Loans and Leases Receivable, Deferred Income, Total										42,120			$ 42,120		$ 42,120	$ 90,307
Weighted Average Remaining Accretion Period of Deferred Revenue (Month)													1 year 60 days			330 days
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total										$ 31,100			$ 31,100		$ 31,100	$ 48,100
Percentage of Financing Receivable, Short-term Payment Deferral										5.20%			5.20%		5.20%
Percentage of Financing Receivable, Short-term Payment Deferral, Actively Enrolled										1.40%			1.40%		1.40%
Financing Receivable, Short-term Payment Deferral										$ 19,100			$ 19,100		$ 19,100
Financing Receivable, Modifications, Number of Contracts															66,667		24,831
Financing Receivable, Troubled Debt Restructuring										$ 78,200	$ 36,400		$ 78,200	$ 36,400	$ 78,200		$ 36,400
Effective Income Tax Rate Reconciliation, Percent, Total										19.60%	21.10%		18.90%	20.00%
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total										$ 0			$ 100
Income Tax Settlement Amount with Taxing Authority									$ 7,400
Tax Adjustments, Settlements, and Unusual Provisions								$ 3,700
Payment of Income Tax Settlement							$ 5,400					$ 500				$ 700
Abatement Sought for Failure-to-pay Penalties										$ 900			900		$ 900
Proceeds from Issuance of Long-term Debt, Total			$ 100,000	$ 200,000	$ 200,000	$ 167,300							$ 249,353	$ 527,866
Subsequent Event [Member]
Proceeds from Dividends Received	$ 2,000
Proceeds from Issuance of Long-term Debt, Total		$ 250,000
Other Income [Member]
Reduction in Accruals											$ 26,700			$ 68,100
Minimum [Member]
Accounts Payable, Extension of Payment Terms (Month)													300 days
Maximum [Member]
Accounts Payable, Extension of Payment Terms (Month)													3 years 30 days