Operating Segments (Schedule Of Sales And Long-Lived Assets By Country) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Sales and other operating revenues	$ 632,094	$ 505,049	$ 475,921	$ 296,915	$ 671,723	$ 636,107	$ 539,604	$ 379,719	$ 1,909,979	$ 2,227,153	$ 2,033,947
Long-Lived Assets	459,840				400,488				459,840	400,488	422,721
Belgium [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									361,889	390,433	339,391
United States [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									221,428	227,771	249,281
Long-Lived Assets	145,764				81,270				145,764	81,270	88,196
China [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									105,683	115,174	120,859
Germany [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									104,525	166,397	114,386
Poland
Segment Reporting Information [Line Items]
Sales and other operating revenues									84,011	145,478	110,445
Indonesia (Member)
Segment Reporting Information [Line Items]
Sales and other operating revenues									80,891	104,268	73,544
Philippines
Segment Reporting Information [Line Items]
Sales and other operating revenues									68,143	69,820	52,902
Brazil [Member]
Segment Reporting Information [Line Items]
Long-Lived Assets	138,157				139,624				138,157	139,624	141,087
Mozambique [Member]
Segment Reporting Information [Line Items]
Long-Lived Assets	42,964				45,051				42,964	45,051	47,800
All Other Countries [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									883,409	1,007,812	973,139
Long-Lived Assets	$ 132,955				$ 134,543				$ 132,955	$ 134,543	$ 145,638