Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment information
Revenue									$ 1,687,085	$ 1,383,279	$ 1,522,592
Derivative (loss) gain not allocated to segments									(24,638)	56,535	(29,035)
Total revenue	453,538	420,516	415,120	373,273	369,153	280,576	442,822	347,263	1,662,447	1,439,814	1,493,557
Total segments
Segment information
Revenue									1,693,267	1,389,214	1,536,539
Unallocated Segment
Segment information
Derivative (loss) gain not allocated to segments									(24,638)	56,535	(29,035)
Revenue deferral adjustment and other									$ (6,182)	$ (5,935)	$ (13,947)