Note 20 - Business Segments - Revenue From Major Customers (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues		$ 662,591	$ 594,644	$ 559,524
Southern California Edison Company [Member]
Revenues	[1]	$ 33,552	$ 56,026	$ 75,803
Percentage of revenues	[1]	5.10%	9.40%	13.50%
Southern California Public Power Authority [Member]
Revenues		$ 67,566	$ 30,947	$ 21,799
Percentage of revenues		10.20%	5.20%	3.90%
Sierra Pacific Power Company And Nevada Power Company [Member]
Revenues	[1],[2]	$ 127,226	$ 115,876	$ 92,580
Percentage of revenues	[1],[2]	19.20%	19.50%	16.50%
Hyundai [Member]
Revenues	[3]	$ 100,856	$ 93,131	$ 38,174
Percentage of revenues	[3]	15.20%	15.70%	6.80%
Kenya Power And Lighting Co LTD [Member]
Revenues	[1]	$ 109,270	$ 86,545	$ 86,074
Percentage of revenues	[1]	16.50%	14.60%	15.40%

[1] Revenues reported in Electricity segment.

[2] Subsidiaries of NV Energy, Inc.

[3] Revenues related to the Sarulla project that are reported in Products segment.