Year	US Dollars
1972	3610
1973	4680
1974	5800
1975	6730
1976	7140
1977	7680
1978	8880
1979	11070
1980	13030
1981	12560
1982	11140
1983	10040
1984	9890
1985	9850
1986	11260
1987	14260
1988	18650
1989	19790
1990	21340
1991	22920
1992	25860
1993	25990
1994	27530
1995	29560
1996	30910
1997	30200
1998	27990
1999	26880
2000	26210
2001	24790
2002	23710
2003	26230
2004	31730
2005	35880
2006	38370
2007	40700
2008	43870
2009	43810
2010	44790
2011	47360
2012	46710
2013	47410
2014	47710
2015	45790
2016	44020
2017	43490