Operating Segments (Schedule Of Sales And Long-Lived Assets By Country) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Sales and other operating revenues	$ 671,723	$ 636,107	$ 539,604	$ 379,719	$ 607,496	$ 653,581	$ 488,248	$ 284,622	$ 2,227,153	$ 2,033,947	$ 2,071,218
Long-Lived Assets	400,488				422,721				400,488	422,721	416,228
Belgium [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									390,433	339,391	320,735
United States [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									227,771	249,281	320,731
Long-Lived Assets	81,270				88,196				81,270	88,196	85,145
China [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									115,174	120,859	137,855
Germany [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									166,397	114,386	123,649
Poland
Segment Reporting Information [Line Items]
Sales and other operating revenues									145,478	110,445	94,681
Indonesia (Member)
Segment Reporting Information [Line Items]
Sales and other operating revenues									104,268	73,544	57,206
Philippines
Segment Reporting Information [Line Items]
Sales and other operating revenues									69,820	52,902	92,288
Mexico
Segment Reporting Information [Line Items]
Sales and other operating revenues									64,700	62,891	50,540
Brazil [Member]
Segment Reporting Information [Line Items]
Long-Lived Assets	139,624				141,087				139,624	141,087	134,074
Mozambique [Member]
Segment Reporting Information [Line Items]
Long-Lived Assets	45,051				47,800				45,051	47,800	50,311
All Other Countries [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									943,112	910,248	873,533
Long-Lived Assets	$ 134,543				$ 145,638				$ 134,543	$ 145,638	$ 146,698