Year	US Dollars
1970	1493947000
1971	1998462000
1972	2613789000
1973	2881231000
1974	2722901000
1975	2290473000
1976	4998743000
1977	10790569000
1978	16630900000
1979	24101914000
1980	29382195000
1981	32151264000
1982	32181845000
1983	38321052000
1984	36900073000
1985	35344222000
1986	34349097000
1987	34576905000
1988	34742786000
1989	32380476000
1990	33172571000
1991	34123003000
1992	37849462000
1993	37540190000
1994	36943074000
1995	35744354000
1996	34763666000
1997	39947610000
1998	44179410000
1999	43484308000
2000	42753311000
2001	39552750000
2002	37132966000
2003	38105848000
2004	39193252000
2005	45357224000
2006	45167276000
2007	58712126000
2008	66930078000
2009	84578254000
2010	101765867000
2011	118171694000
2012	130629842000
2013	132345779000
2014	135747695000
2015	124386152000
2016	113023864000