Note 12 - Employee Benefit Plan (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	60.00%
Defined Contribution Plan, Cost	$ 7.3	$ 5.9	$ 4.8
Amount Contributed on Percentage of Pay, Tier One [Member] | The 401(k) Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	100.00%	100.00%	100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	4.00%	3.00%	3.00%
Amount Contributed on Percentage of Pay, Tier Two [Member] | The 401(k) Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%	50.00%	50.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	1.00%	2.00%	2.00%