Note 9 - Quarterly Results for 2018, 2017, and 2016 (Unaudited) (Details Textual) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense (Benefit), Total	$ 5,000				$ 4,420	$ 9,760	$ 5,260
Tax Adjustments, Settlements, and Unusual Provisions	$ 4,000					$ 4,000
Reclassification from APIC to Income Tax Expense [Member] | Three Months Ended March 31, 2016 [Member]
Prior Period Reclassification Adjustment				$ 200
Reclassification from APIC to Income Tax Expense [Member] | Three Months Ended June 30, 2016 [Member]
Prior Period Reclassification Adjustment			$ 200
Reclassification from APIC to Income Tax Expense [Member] | Three Months Ended September 30, 2016 [Member]
Prior Period Reclassification Adjustment		$ 100