Year	U.S. dollars (Units)
1980	684.569
1981	584.519
1982	541.617
1983	513.524
1984	490.137
1985	482.697
1986	629.744
1987	741.276
1988	772.133
1989	731.080
1990	868.945
1991	895.707
1992	955.474
1993	916.695
1994	660.355
1995	806.805
1996	789.145
1997	714.272
1998	701.452
1999	703.067
2000	628.071
2001	675.050
2002	757.399
2003	949.680
2004	1055.357
2005	1085.659
2006	1110.984
2007	1251.857
2008	1403.796
2009	1351.145
2010	1322.638
2011	1450.159
2012	1403.417
2013	1500.731
2014	1505.178
2015	1231.135
2016	1256.035
2017	1300.566
2018	1386.014
2019	1359.750
2020	1357.291
2021	1381.767
2022	1281.795
2023	1352.918
2024	1384.485
2025	1421.304
2026	1460.721
2027	1493.222
2028	1522.976
2029	1552.404