Quarter	Millions of US Dollars
2007-01-01	0
2007-04-01	0
2007-07-01	0
2007-10-01	0
2008-01-01	0
2008-04-01	0
2008-07-01	0
2008-10-01	0
2009-01-01	0
2009-04-01	0
2009-07-01	0
2009-10-01	0
2010-01-01	0
2010-04-01	500
2010-07-01	500
2010-10-01	500
2011-01-01	700
2011-04-01	200
2011-07-01	200
2011-10-01	200
2012-01-01	0
2012-04-01	0
2012-07-01	0
2012-10-01	0
2013-01-01	0
2013-04-01	0
2013-07-01	0
2013-10-01	0
2014-01-01	0
2014-04-01	0
2014-07-01	250
2014-10-01	250
2015-01-01	250
2015-04-01	250
2015-07-01	150
2015-10-01	150
2016-01-01	150
2016-04-01	400
2016-07-01	750
2016-10-01	750
2017-01-01	750
2017-04-01	500
2017-07-01	0
2017-10-01	0
2018-01-01	0
2018-04-01	0