Note 4 - Loans and Allowance for Loan Losses (Details Textual)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Loans and Leases Receivable, Gross	$ 6,225,000,000		$ 6,225,000,000			$ 5,633,000,000
Impaired Financing Receivable, Recorded Investment	57,126,000		57,126,000			43,696,000
Impaired Financing Receivable, Related Allowance	5,524,000		5,524,000			680,000
Impaired Financing Receivable, Interest Income, Accrual Method	376,000	$ 449,000	700,000	$ 800,000
Impaired Financing Receivable, Average Recorded Investment	57,256,000	38,777,000	52,736,000	31,914,000
Financing Receivable, Specific Reserve	0		33,000	$ 324,000
Financing Receivable, Modifications, Subsequent Default, Number of Contracts				0
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 41,000	$ 1,395,000	$ 8,629,000	$ 10,361,000
Financing Receivable, Modifications, Number of Contracts	4	18	12	46
Mortgage Loans in Process of Foreclosure, Amount	$ 1,321,000		$ 1,321,000			1,714,000
Real Estate Acquired Through Foreclosure	26,012,000		26,012,000			26,895,000
Loans and Leases Receivable Classified	33,200,000		33,200,000			47,800,000
Loans and Leases Receivable, Allowance	41,379,000		41,379,000			36,286,000
Provision for Loan and Lease Losses	7,023,000	$ 4,616,000	11,330,000	$ 7,439,000
Risk Ratings 6,7, and 8 [Member]
Loans and Leases Receivable Classified	156,100,000		156,100,000			166,000,000
Substandard [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	8,400,000		8,400,000			17,800,000
OREO Secured by Residential Real Estate Properties [Member]
Real Estate Acquired Through Foreclosure	2,648,000		2,648,000			5,094,000
Acquired Loans [Member]
Loans and Leases Receivable, Gross	1,224,739,000		1,224,739,000			1,305,683,000
Provision for Loan and Lease Losses	714,000	307,000	1,464,000	307,000
Allowance for Loan and Lease Losses, Write-offs	758,000		2,000,000	307,000
Loans and Leases Receivable, Allowance, Covered	391,000	954,000	391,000	954,000	$ 435,000	954,000	$ 954,000
Loans, Including Acquired Loans [Member]
Loans and Leases Receivable, Allowance	41,770,000	34,477,000	41,770,000	34,477,000	$ 38,300,000	37,240,000	$ 33,635,000	$ 32,305,000
OREO Received in Full or Partial Satisfaction of Loans [Member] | Commercial Real Estate and Residential Real Estate [Member]
Financing Receivable, Modifications, Pre-Modification Recorded Investment			117,000	166,500
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable, Gross	3,562,015,000		3,562,015,000			3,028,079,000
Impaired Financing Receivable, Recorded Investment	35,851,000		35,851,000			30,001,000
Impaired Financing Receivable, Related Allowance	1,888,000		1,888,000			417,000
Impaired Financing Receivable, Interest Income, Accrual Method	249,000	391,000	464,000	693,000
Impaired Financing Receivable, Average Recorded Investment	37,987,000	34,097,000	$ 35,325,000	27,737,000
Financing Receivable, Modifications, Subsequent Default, Number of Contracts			1
Financing Receivable, Modifications, Pre-Modification Recorded Investment		$ 966,000	$ 7,818,000	$ 9,758,000
Financing Receivable, Modifications, Number of Contracts		8	3	34
Commercial Real Estate Portfolio Segment [Member] | Acquired Loans [Member]
Loans and Leases Receivable, Gross	$ 1,068,842,000		$ 1,068,842,000			$ 1,170,871,000