Year	U.S. dollars (Units)
1980	609.433
1981	510.028
1982	458.113
1983	395.659
1984	310.002
1985	295.810
1986	378.695
1987	430.394
1988	426.027
1989	394.734
1990	435.341
1991	394.900
1992	393.718
1993	343.177
1994	211.016
1995	241.954
1996	243.965
1997	224.475
1998	250.234
1999	231.660
2000	197.275
2001	207.769
2002	227.424
2003	267.410
2004	285.390
2005	320.925
2006	335.336
2007	389.258
2008	477.272
2009	462.269
2010	476.064
2011	511.490
2012	528.921
2013	551.557
2014	562.888
2015	484.173
2016	497.885
2017	517.589
2018	570.983
2019	554.124
2020	568.606
2021	593.802
2022	592.241
2023	610.635
2024	670.104
2025	700.750
2026	731.300
2027	760.263
2028	791.826
2029	824.130