Note 14 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Cash and due from banks		$ 206,123	$ 225,333
Short-term investments		351,603	374,957
Securities available-for-sale		1,471,584	1,242,509
Loans, net	[1]	14,814,173	13,928,162
Equity securities		32,498	25,098
Investment in Federal Home Loan Bank stock		17,250	17,250
Warrants		1,440	7,810
Deposits		14,417,628	13,754,028
Advances from Federal Home Loan Bank		551,591	529,500
Other borrowings		43,084	34,031
Long-term debt		121,592	132,615
Equity Securities, FV-NI		32,498	25,098
Warrants [Member]
Warrants		44
Warrants			184
Fair Value, Inputs, Level 1 [Member]
Cash and due from banks		206,123	225,333
Short-term investments		351,603	374,957
Securities available-for-sale		49,791	124,751
Loans, net	[1]	0	0
Equity securities		32,498	25,098
Investment in Federal Home Loan Bank stock		0	0
Deposits		0	0
Advances from Federal Home Loan Bank		0	0
Other borrowings		0	0
Long-term debt		0	0
Equity Securities, FV-NI		32,498	25,098
Fair Value, Inputs, Level 1 [Member] | Warrants [Member]
Warrants		0
Warrants			0
Fair Value, Inputs, Level 2 [Member]
Cash and due from banks		0	0
Short-term investments		0	0
Securities available-for-sale		1,421,793	1,117,758
Loans, net	[1]	0	0
Equity securities		0	0
Investment in Federal Home Loan Bank stock		17,250	17,250
Deposits		0	0
Advances from Federal Home Loan Bank		551,591	529,500
Other borrowings		0	0
Long-term debt		121,592	132,615
Equity Securities, FV-NI		0	0
Fair Value, Inputs, Level 2 [Member] | Warrants [Member]
Warrants		0
Warrants			0
Fair Value, Inputs, Level 3 [Member]
Cash and due from banks		0	0
Short-term investments		0	0
Securities available-for-sale		0	0
Loans, net	[1]	14,814,173	13,928,162
Equity securities		0	0
Investment in Federal Home Loan Bank stock		0	0
Deposits		14,417,628	13,754,028
Advances from Federal Home Loan Bank		0	0
Other borrowings		43,084	34,031
Long-term debt		0	0
Equity Securities, FV-NI		0	0
Fair Value, Inputs, Level 3 [Member] | Warrants [Member]
Warrants		$ 44
Warrants			$ 184

[1] In accordance with the prospective adoption of ASU 2016-01, the fair value of loans as of December 31, 2018 was measured using an exit price notion. The fair value of loans as of December 31, 2017 was measured using an entry price notion.