Note 4 - Loans and Allowance for Loan Losses - Retail Credit Exposure (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans	$ 2,558,552,000	$ 2,378,620,000
Retail Portfolio Segment [Member]
Loans	354,984,000	313,273,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Loans	100,425,000	118,047,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Loans	254,559,000	195,226,000
Originated Loan [Member]
Loans	2,169,957,000	1,884,548,000	$ 1,616,587,000
Originated Loan [Member] | Retail Portfolio Segment [Member]
Loans	235,729,000	155,650,000	$ 123,071,000
Originated Loan [Member] | Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Loans	69,675,000	69,831,000
Originated Loan [Member] | Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Loans	166,054,000	85,819,000
Acquired Loan [Member]
Loans	388,595,000	494,072,000
Acquired Loan [Member] | Retail Portfolio Segment [Member]
Loans	119,255,000	157,623,000
Acquired Loan [Member] | Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Loans	30,750,000	48,216,000
Acquired Loan [Member] | Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Loans	$ 88,505,000	$ 109,407,000