Year	US Dollars
1972	2990
1973	4000
1974	4970
1975	4980
1976	4680
1977	4560
1978	5220
1979	6570
1980	7680
1981	8260
1982	7780
1983	7330
1984	6990
1985	6940
1986	7920
1987	9680
1988	12440
1989	13680
1990	13760
1991	12150
1992	12050
1993	12390
1994	13440
1995	15250
1996	16670
1997	17250
1998	15860
1999	15030
2000	14020
2001	13810
2002	14230
2003	16990
2004	21390
2005	25380
2006	26350
2007	28280
2008	28640
2009	30050
2010	29770
2011	32270
2012	36840
2013	39730
2014	41490
2015	40270
2016	38560
2017	38970