Risk Concentrations (Schedule of Foreign Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Revenues	$ 549,480	$ 619,467	$ 570,222	$ 555,183	$ 650,963	$ 633,180	$ 592,349	$ 575,295	$ 2,294,352	$ 2,451,787	$ 2,324,623
Europe
Concentration Risk [Line Items]
Revenues									537,117	559,165	388,926
Asia
Concentration Risk [Line Items]
Revenues									322,029	452,711	264,503
Central and South America
Concentration Risk [Line Items]
Revenues									82,476	79,085	30,982
Africa
Concentration Risk [Line Items]
Revenues									18,698	17,567	14,901
Brokered Sales
Concentration Risk [Line Items]
Revenues									0	2,372	3,150
Foreign Countries
Concentration Risk [Line Items]
Revenues									$ 960,320	$ 1,110,900	$ 702,462