Year	U.S. dollars (Units)
1980	1552.837
1981	1481.175
1982	1005.587
1983	1377.269
1984	1618.263
1985	1344.575
1986	1044.670
1987	1219.750
1988	1217.822
1989	983.644
1990	999.179
1991	1503.376
1992	1778.897
1993	2290.378
1994	2641.040
1995	3109.262
1996	3551.799
1997	4246.445
1998	4618.673
1999	4582.361
2000	4428.662
2001	4349.954
2002	4504.149
2003	4440.345
2004	4630.727
2005	4575.074
2006	4626.820
2007	5207.760
2008	6111.360
2009	7354.971
2010	7761.616
2011	7675.291
2012	7948.646
2013	7928.317
2014	7681.707
2015	7642.960
2016	7617.732
2017	7776.012
2018	8003.824
2019	7421.491
2020	3588.705
2021	3044.801
2022	3283.414