Year	U.S. dollars (Units)
1980	460.392
1981	447.790
1982	416.180
1983	419.657
1984	400.328
1985	358.713
1986	354.471
1987	327.758
1988	354.718
1989	384.328
1990	420.593
1991	523.591
1992	422.469
1993	483.263
1994	278.145
1995	319.894
1996	512.064
1997	583.417
1998	373.078
1999	368.272
2000	352.650
2001	338.478
2002	384.137
2003	345.163
2004	365.696
2005	377.042
2006	400.898
2007	432.115
2008	504.650
2009	571.113
2010	623.414
2011	695.331
2012	506.300
2013	446.999
2014	484.322
2015	497.737
2016	415.016
2017	466.559
2018	501.113
2019	543.685
2020	567.590
2021	580.967
2022	566.790
2023	577.538
2024	480.727
2025	471.082
2026	472.643
2027	485.061
2028	498.686
2029	513.443