Quarter	Millions of US Dollars
1979-01-01	30
1987-01-01	-32
1994-01-01	174
1999-04-01	216
1999-07-01	1115
1999-10-01	40
2000-01-01	1029
2000-04-01	626
2000-07-01	259
2000-10-01	954
2001-01-01	1859
2001-04-01	132
2001-07-01	1667
2001-10-01	3399
2002-01-01	2402
2002-04-01	2135
2002-07-01	3000
2002-10-01	3256
2003-01-01	4581
2003-04-01	5835
2003-07-01	1405
2003-10-01	2952
2004-01-01	5810
2004-04-01	937
2004-07-01	1427
2004-10-01	4654
2005-01-01	5573
2005-04-01	9004
2005-07-01	2502
2005-10-01	8206
2006-01-01	12645
2006-04-01	5507
2006-07-01	5498
2006-10-01	785
2007-01-01	7007
2007-04-01	4683
2007-07-01	667
2007-10-01	1021
2008-01-01	-1308
2008-04-01	4645
2008-07-01	-1013
2008-10-01	-970
2009-01-01	1937
2009-04-01	-771
2009-07-01	-4159
2009-10-01	3779
2010-01-01	-3486
2010-04-01	-5642
2010-07-01	5199
2010-10-01	-1521
2011-01-01	-2153
2011-04-01	2543
2011-07-01	-4767
2011-10-01	-2297
2012-01-01	-14560
2012-04-01	899
2012-07-01	973
2012-10-01	961
2013-01-01	-3990
2013-04-01	-2857
2013-07-01	-3591
2013-10-01	-801
2014-01-01	-5104
2014-04-01	-1948
2014-07-01	1317
2014-10-01	2690
2015-01-01	-2733
2015-04-01	2234
2015-07-01	394
2015-10-01	-4888
2016-01-01	489
2016-04-01	-14858
2016-07-01	1382
2016-10-01	1370
2017-01-01	-386
2017-04-01	-3354
2017-07-01	6317
2017-10-01	7471
2018-01-01	3300
2018-04-01	2412