Year	US Dollars, Monthly Level
1971-01-01	3247393000
1972-01-01	4232348000
1973-01-01	6192238000
1974-01-01	12641320000
1975-01-01	12210340000
1976-01-01	12382982000
1977-01-01	12023412000
1978-01-01	13683146000
1979-01-01	18083861000
1980-01-01	22955169000
1981-01-01	22090580000
1982-01-01	19394998000
1983-01-01	15428925000
1984-01-01	13915821000
1985-01-01	13153491000
1986-01-01	14044304000
1987-01-01	15050827000
1988-01-01	14605254000
1989-01-01	18263432738
1990-01-01	20661362039
1991-01-01	21040470792
1992-01-01	20554091051
1993-01-01	25256000927
1994-01-01	33078690132
1995-01-01	49971896207
1996-01-01	53345767156
1997-01-01	59484840278
1998-01-01	57596907511
1999-01-01	49181644327
2000-01-01	55891118709
2001-01-01	55444566162
2002-01-01	47140165638
2003-01-01	48269929600
2004-01-01	62744505513
2005-01-01	73468391463
2006-01-01	91192855350
2007-01-01	120475382973
2008-01-01	173118588785
2009-01-01	127812153899
2010-01-01	181774969378
2011-01-01	226244222128
2012-01-01	223366721023
2013-01-01	239681231635
2014-01-01	229127843314
2015-01-01	171458999759
2016-01-01	137585830976
2017-01-01	150749494421