Financing (Details 7) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Gain (loss) from changes in fair value of hybrid instruments	$ (299)	$ (31,170)
Debentures 2006 Series [Member]
Gain (loss) from changes in fair value of hybrid instruments	1,887	0
Debentures 2007 Series [Member]
Gain (loss) from changes in fair value of hybrid instruments	2,329	(25,057)
Debentures 2008 Series [Member]
Gain (loss) from changes in fair value of hybrid instruments	1,657	6,113
Debentures 2009 Series [Member]
Gain (loss) from changes in fair value of hybrid instruments	(74)	0
Debentures 2010 Series [Member]
Gain (loss) from changes in fair value of hybrid instruments	623	0
Debentures 2011 Series [Member]
Gain (loss) from changes in fair value of hybrid instruments	249	0
Debentures 2012 Series [Member]
Gain (loss) from changes in fair value of hybrid instruments	$ 103	$ 0