Year	US Dollars
1970	2440
1971	2720
1972	3150
1973	3840
1974	4290
1975	4800
1976	4930
1977	5140
1978	5840
1979	7450
1980	9380
1981	10480
1982	10470
1983	9690
1984	9110
1985	9000
1986	10070
1987	12480
1988	15880
1989	17080
1990	18250
1991	19060
1992	21110
1993	21000
1994	21520
1995	20820
1996	22490
1997	24930
1998	26400
1999	27720
2000	28880
2001	28630
2002	28900
2003	31990
2004	37690
2005	42770
2006	45000
2007	47760
2008	48420
2009	43940
2010	41380
2011	40620
2012	41200
2013	42340
2014	43740
2015	43720
2016	42370
2017	40530