Note 8 - Fair Value - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Securities	$ 42,048	$ 60,193
Fair Value, Inputs, Level 1 [Member]
Securities	0	0
Fair Value, Inputs, Level 2 [Member]
Securities	42,048	60,193
Fair Value, Inputs, Level 3 [Member]
Securities	0	0
Reported Value Measurement [Member]
Cash and cash equivalents	429,665	190,325
Securities	42,048	60,193
Loans receivable, net of allowance for loan losses	1,065,892	1,168,008
FHLB and FRB stock	7,490	7,490
Accrued interest receivable	4,354	4,563
Certificates of deposit	301,351	402,034
Borrowings	4,000	61
Estimate of Fair Value Measurement [Member]
Cash and cash equivalents	429,665	190,325
Securities	42,048	60,193
Loans receivable, net of allowance for loan losses	1,073,308	1,177,459
Accrued interest receivable	4,354	4,563
Certificates of deposit	302,791	402,914
Borrowings	3,997	61
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	13,740	9,785
Securities	0	0
Loans receivable, net of allowance for loan losses	0	0
FHLB and FRB stock	0	0
Accrued interest receivable	0	0
Certificates of deposit	0	0
Borrowings	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	415,925	180,540
Securities	42,048	60,193
Loans receivable, net of allowance for loan losses	0	0
FHLB and FRB stock	0	0
Accrued interest receivable	158	252
Certificates of deposit	302,791	402,914
Borrowings	3,997	61
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0	0
Securities	0	0
Loans receivable, net of allowance for loan losses	1,073,308	1,177,459
FHLB and FRB stock	0	0
Accrued interest receivable	4,196	4,311
Certificates of deposit	0	0
Borrowings	$ 0	$ 0