Year	U.S. dollars (Units)
1980	4157.553
1981	4608.557
1982	3743.307
1983	2041.642
1984	1929.090
1985	1873.063
1986	2312.365
1987	2876.920
1988	2958.929
1989	3101.177
1990	3588.340
1991	4299.367
1992	4911.064
1993	5683.683
1994	6557.811
1995	7207.021
1996	7612.913
1997	7959.731
1998	8364.608
1999	7847.880
2000	7432.339
2001	6803.597
2002	4441.095
2003	3941.678
2004	4476.943
2005	5663.499
2006	6377.451
2007	7622.824
2008	9857.304
2009	10232.122
2010	12943.943
2011	15341.308
2012	16325.410
2013	18271.525
2014	18109.936
2015	16791.911
2016	16544.810
2017	18626.981
2018	18645.281
2019	17686.109
2020	15198.839
2021	17149.709
2022	19737.342
2023	21656.979
2024	23087.682
2025	24044.448
2026	25033.016
2027	26088.201
2028	27229.474
2029	28431.828