Year	U.S. dollars (Units)
1980	599.371
1981	534.073
1982	522.936
1983	498.801
1984	404.876
1985	383.873
1986	427.478
1987	307.636
1988	297.420
1989	288.402
1990	347.714
1991	280.355
1992	311.649
1993	331.998
1994	279.380
1995	295.539
1996	368.663
1997	309.351
1998	310.104
1999	292.558
2000	307.335
2001	350.500
2002	334.838
2003	387.055
2004	298.635
2005	335.388
2006	355.397
2007	459.855
2008	561.654
2009	488.901
2010	492.670
2011	553.450
2012	538.541
2013	560.939
2014	548.905
2015	481.807
2016	489.439
2017	528.379
2018	535.948
2019	531.750
2020	477.375
2021	516.529
2022	527.757
2023	529.224
2024	538.176
2025	569.802
2026	596.180
2027	625.025
2028	665.639
2029	709.544