Note 6 - Accumulated Other Comprehensive Loss - Disclosure of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Balance	$ 761,261		$ 554,320		$ 397,179
Net current-period other comprehensive income (loss)	(1,104)		(2,615)		18,965
Balance	1,032,851		761,261		554,320
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Balance	(18,832)		(12,856)
Other comprehensive income (loss) before reclassifications	2,210		(5,976)
Amounts reclassified from AOCL	0		0
Net current-period other comprehensive income (loss)	2,210		(5,976)
Balance	(16,622)		(18,832)		(12,856)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance	(10,541)		(10,978)
Other comprehensive income (loss) before reclassifications	1,474	[1]	(156)	[2]
Amounts reclassified from AOCL	9,067	[3]	593	[4]
Net current-period other comprehensive income (loss)	10,541		437
Balance	0		(10,541)		(10,978)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Balance	5,560		2,636
Other comprehensive income (loss) before reclassifications	(13,855)	[5]	2,924	[6]
Amounts reclassified from AOCL	0		0
Net current-period other comprehensive income (loss)	(13,855)		2,924
Balance	(8,295)		5,560		2,636
AOCI Attributable to Parent [Member]
Balance	(23,813)		(21,198)		(40,163)
Other comprehensive income (loss) before reclassifications	(10,171)		(3,208)
Amounts reclassified from AOCL	9,067		593
Net current-period other comprehensive income (loss)	(1,104)		(2,615)
Balance	$ (24,917)		$ (23,813)		$ (21,198)

[1] Represents unrecognized actuarial gains of $1,992 net of tax effect of $(518), included in the computation of net periodic pension cost for the year ended December 31, 2019. Refer to Note 16, "Benefit Plans," to the consolidated financial statements for additional information.

[2] Represents unrecognized actuarial losses of $(211), net of tax benefit of $55, included in the computation of net periodic pension cost for the year ended December 31, 2018. Refer to Note 16, "Benefit Plans," to the consolidated financial statements for additional information.

[3] Details of reclassifications from AOCL during 2019 are as follows: Amounts reclassified from AOCL Loss on pension settlement $ 10,920 Amortization of net loss 843 Total before tax 11,763 Income tax impact (2,696 ) Amounts reclassified from AOCL $ 9,067

[4] Represents actuarial losses of $802, net of tax effect of $(209), amortized to net periodic pension cost for the year ended December 31, 2018. Refer to Note 16, "Benefit Plans," to the consolidated financial statements for additional information.

[5] Represents unrealized losses of $(18,732), net of tax effect of $4,877 for the year ended December 31, 2019.

[6] Represents unrealized gains of $3,951, net of tax effect of $(1,027) for the year ended December 31, 2018.