Shareholders' Equity - Reclassification of Amounts Out of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Tax expense (benefit)	$ 143,643	$ 104,129	$ 191,684	$ 256,927
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Cash Flow Hedges
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Tax expense (benefit)	(716)	(1,640)	(1,704)	(3,482)
Net of tax	1,215	2,804	2,891	5,957
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Cash Flow Hedges | Interest Expense
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Settlements of derivatives	1,931	4,444	4,595	9,439
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Investments Available for Sale
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Discount accretion	0		0
Tax expense (benefit)	0	164	0	351
Net of tax	0	(279)	0	(600)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Investments Available for Sale | Interest Expense
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Discount accretion		$ (443)		$ (951)