Quarter	Millions of US Dollars
1998-01-01	18306
1998-04-01	-38067
1998-07-01	37001
1998-10-01	-56852
1999-01-01	54245
1999-04-01	-22044
1999-07-01	17364
1999-10-01	15108
2000-01-01	-26664
2000-04-01	-62469
2000-07-01	-7588
2000-10-01	8602
2001-01-01	25955
2001-04-01	79064
2001-07-01	93650
2001-10-01	55912
2002-01-01	64554
2002-04-01	38354
2002-07-01	54581
2002-10-01	80653
2003-01-01	105135
2003-04-01	28200
2003-07-01	3832
2003-10-01	26831
2004-01-01	72121
2004-04-01	3529
2004-07-01	89252
2004-10-01	90934
2005-01-01	124639
2005-04-01	28244
2005-07-01	17649
2005-10-01	271886
2006-01-01	28572
2006-04-01	-63230
2006-07-01	25130
2006-10-01	-12993
2007-01-01	9464
2007-04-01	-9629
2007-07-01	-12635
2007-10-01	5704
2008-01-01	-5812
2008-04-01	-80720
2008-07-01	-22164
2008-10-01	-11948
2009-01-01	-67089
2009-04-01	-69111
2009-07-01	19115
2009-10-01	-22577
2010-01-01	-24498
2010-04-01	38604
2010-07-01	1359
2010-10-01	-56032
2011-01-01	-92408
2011-04-01	-24017
2011-07-01	-40077
2011-10-01	1947
2012-01-01	-14874
2012-04-01	108
2012-07-01	-36843
2012-10-01	74517
2013-01-01	-31364
2013-04-01	-55319
2013-07-01	-24219
2013-10-01	-8356
2014-01-01	-2842
2014-04-01	-32309
2014-07-01	-9750
2014-10-01	14484
2015-01-01	2357
2015-04-01	-30154
2015-07-01	2075
2015-10-01	14904
2016-01-01	170929
2016-04-01	-96377
2016-07-01	-44162
2016-10-01	-1069
2017-01-01	29085
2017-04-01	-26894
2017-07-01	-14888
2017-10-01	23267
2018-01-01	33646