Note 10 - Accumulated Other Comprehensive Loss - Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Balance beginning of period			$ 461,215
Balance at end of period	$ 531,206		531,206
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Balance beginning of period	(6,359)	$ (7,404)	(5,234)	$ (10,753)
Other comprehensive income (loss) before reclassifications	(879)	1,655	(2,004)	5,004
Amounts reclassified from accumulated other comprehensive loss
Net current-period other comprehensive income (loss)	(879)	1,655	(2,004)	5,004
Balance at end of period	$ (7,238)	$ (5,749)	$ (7,238)	$ (5,749)