Note 19 - Business Segments (Details) - Summarized Financial Information Concerning Reportable Segments (USD $) In Thousands, unless otherwise specified	3 Months Ended							12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Mar. 31, 2013
Segment Reporting Information [Line Items]
Net revenues from external customers	$ 130,905		$ 130,749	$ 152,679	$ 132,297	$ 126,708	$ 132,352	$ 533,239		$ 501,773		$ 425,456
Intersegment revenues								533,239	[1]	501,773	[1]	425,456	[1]
Depreciation and amortization expense								92,932		99,484		93,534
Operating income	21,615		29,797	37,862	12,065	24,383	25,742	96,958		(159,896)		61,555
Segment assets at period end *	2,159,433	[2]						2,159,433	[2]	2,087,523	[2]	2,314,718	[2]	2,133,925
Expenditures for long-lived assets								204,628		233,020		269,677
* Including unconsolidated investments	7,076							7,076		3,757		2,591
Electricity Member
Segment Reporting Information [Line Items]
Net revenues from external customers								329,747		314,894		312,296
Depreciation and amortization expense								88,853		95,927		90,464
Operating income								54,265		(189,994)		42,926
Segment assets at period end *	2,017,838	[2]						2,017,838	[2]	1,990,490	[2]	2,222,836	[2]
Expenditures for long-lived assets								203,047		228,289		266,258
* Including unconsolidated investments	7,076							7,076		2,215		2,591
Product Segment [Member]
Segment Reporting Information [Line Items]
Net revenues from external customers								203,492		186,879		113,160
Intersegment revenues								37,248		48,315		80,712
Depreciation and amortization expense								4,079		3,557		3,070
Operating income								42,693		30,098		18,629
Segment assets at period end *	141,595	[2]						141,595	[2]	97,033	[2]	91,882	[2]
Expenditures for long-lived assets								1,581		4,731		3,419
* Including unconsolidated investments										1,542
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Intersegment revenues								$ 37,248		$ 48,315		$ 80,712

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

[2] Including unconsolidated investments