Accumulated Other Comprehensive Loss - Reclassification of Amounts Out of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Tax expense (benefit)	$ (48,041)	$ (152,798)
Unrealized gains (losses) on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Tax expense (benefit)	(988)	(1,842)
Net of tax	1,676	3,153
Unrealized gains (losses) on cash flow hedges | Interest Expense | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Settlements of derivatives	2,664	4,995
Unrealized gains (losses) on investments available for sale | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Tax expense (benefit)		187
Net of tax		(321)
Unrealized gains (losses) on investments available for sale | Interest Expense | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Discount accretion		$ (508)