Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 548,686	$ 720,477	$ 962,542
Derivative financial instruments:
Unrealized holding (loss) gain	(6,833)	4,237	(625)
Reclassification adjustment for loss (gain) included in net income	4,840	2,733	(6,728)
Investments in marketable securities:
Unrealized holding (loss) gain on investments	(6)	124	(46)
Reclassification adjustment for (gain) loss included in net income	(147)	44	(384)
Total other comprehensive (loss) gain	(2,146)	7,138	(7,783)
Comprehensive income	$ 546,540	$ 727,615	$ 954,759