Note 10 - Accumulated Other Comprehensive Loss - Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Balance beginning of period			$ 461,215
Balance at end of period	$ 506,253		506,253
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Balance beginning of period	(2,841)	$ (9,568)	(5,234)	$ (10,753)
Other comprehensive income (loss) before reclassifications	(3,518)	2,164	(1,125)	3,349
Amounts reclassified from accumulated other comprehensive loss
Net current-period other comprehensive income (loss)	(3,518)	2,164	(1,125)	3,349
Balance at end of period	$ (6,359)	$ (7,404)	$ (6,359)	$ (7,404)