Note 4 - Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Available for sale, amortized cost	$ 281,794	$ 209,263
Available for sale, gross unrealized gains	1,080	1,731
Available for sale, gross unrealized losses	(1,292)	(127)
Available for sale	281,582	210,867
Held to maturity (fair value of $7,020 and $7,603 at March 31, 2021 and December 31, 2020, respectively)	6,668	7,174
Held to maturity, gross unrealized gains	352	429
Held to maturity, gross unrealized losses	0	0
Securities held to maturity, fair value	7,020	7,603
US Government Agencies Debt Securities [Member]
Available for sale, amortized cost	1,088	1,257
Available for sale, gross unrealized gains	20	37
Available for sale, gross unrealized losses	0	0
Available for sale	1,108	1,294
Small Business Administration Agency Securities [Member]
Available for sale, amortized cost	4,017	4,125
Available for sale, gross unrealized gains	138	269
Available for sale, gross unrealized losses	0	0
Available for sale	4,155	4,394
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available for sale, amortized cost	30,651	17,415
Available for sale, gross unrealized gains	166	270
Available for sale, gross unrealized losses	(325)	(8)
Available for sale	30,492	17,677
Collateralized Mortgage Obligations [Member]
Available for sale, amortized cost	88,552	48,476
Available for sale, gross unrealized gains	244	491
Available for sale, gross unrealized losses	(470)	(93)
Available for sale	88,326	48,874
Commercial Paper [Member]
Available for sale, amortized cost	119,210	102,462
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	(16)	(14)
Available for sale	119,194	102,448
Corporate Debt Securities [Member]
Available for sale, amortized cost	36,657	33,907
Available for sale, gross unrealized gains	512	662
Available for sale, gross unrealized losses	(426)	(6)
Available for sale	36,743	34,563
Municipal Bonds [Member]
Available for sale, amortized cost	1,619	1,621
Available for sale, gross unrealized gains	0	2
Available for sale, gross unrealized losses	(55)	(6)
Available for sale	1,564	1,617
Held to maturity (fair value of $7,020 and $7,603 at March 31, 2021 and December 31, 2020, respectively)	4,761	4,767
Held to maturity, gross unrealized gains	236	290
Held to maturity, gross unrealized losses	0	0
Securities held to maturity, fair value	4,997	5,057
Taxable Municipal Bonds [Member]
Held to maturity (fair value of $7,020 and $7,603 at March 31, 2021 and December 31, 2020, respectively)	1,907	2,407
Held to maturity, gross unrealized gains	116	139
Held to maturity, gross unrealized losses	0	0
Securities held to maturity, fair value	$ 2,023	$ 2,546

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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