Quarter	Millions of US Dollars
1973-04-01	9
1976-07-01	10
1980-07-01	3
1985-10-01	-1
1987-04-01	-4
1989-01-01	-9
1990-04-01	-7
1998-01-01	1277
1998-07-01	-5
1999-01-01	-5
1999-07-01	-5
2000-01-01	-5
2000-07-01	-5
2001-01-01	-5
2001-07-01	-5
2002-01-01	-5
2002-07-01	-5
2003-01-01	-5
2003-07-01	-6
2004-01-01	-6
2004-07-01	-6
2005-01-01	-6
2005-07-01	-6
2006-01-01	-6
2006-07-01	-6
2007-01-01	-6
2007-07-01	-6
2008-01-01	-9
2008-07-01	-9
2009-01-01	-9
2009-07-01	-9
2010-01-01	-9
2010-04-01	1481
2010-07-01	-13
2011-01-01	-13
2011-07-01	-13
2012-01-01	-13
2012-07-01	-17
2013-01-01	-17
2013-07-01	-17
2014-01-01	-17
2014-07-01	733
2015-01-01	983
2015-07-01	-17
2015-10-01	243
2016-01-01	-17
2016-07-01	-21
2017-01-01	-21
2017-04-01	1954
2017-07-01	-21
2018-01-01	2083