Note 19 - Business Segments - Revenues as Reported in the Geographic Area (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Revenues		$ 190,465	$ 166,480	$ 178,299	$ 184,023	$ 166,365	$ 157,185	$ 179,364	$ 189,898	$ 719,267	[1]	$ 692,812	[1]	$ 662,591	[1]
UNITED STATES
Revenues	[1]									328,606	[2]	301,132		307,025
INDONESIA
Revenues	[1]									4,379		28,968		100,856
KENYA
Revenues	[1]									119,094		110,243		109,270
TURKEY
Revenues	[1]									168,699		125,166		46,270
CHILE
Revenues	[1]									980		8,895		58,032
GUATEMALA
Revenues	[1]									27,975		27,991		30,086
NEW ZEALAND
Revenues	[1]									10,451		33,395
Other Foreign Countries [Member]
Revenues	[1]									$ 59,083		$ 57,022		$ 11,052

[1] Revenues as reported in the geographic area in which they originate.

[2] Electricity segment revenues in the United States are all accounted under ASC 840, Leases, except for $26.9 million for the year ended December 31, 2018 that are accounted under ASC 606 starting in 2018. Product and Other segment revenues in the United States are accounted under ASC 606, as further described under Note 1 to the consolidated financial statements.