Derivatives and Hedging Activities Derivatives and Hedging Activities - Effect of Derivatives on Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated other comprehensive income (loss) from derivative instruments
Unrealized gain (loss) on derivative instruments at beginning of period	$ 86,436
Unrealized gain (loss) on derivative instruments, net	(245,945)	485,653	(423,906)
Balance at the end of period	(156,993)	86,436
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated other comprehensive income (loss) from derivative instruments
Unrealized gain (loss) on derivative instruments at beginning of period	(435,217)	(395,926)	(4,505)
Unrealized gain (loss) on derivative instruments, net	429,151	(39,291)	(391,421)
Balance at the end of period	$ (6,066)	$ (435,217)	$ (395,926)