Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			12 Months Ended	3 Months Ended		6 Months Ended			12 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2012 Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2013 Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2012 Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Dec. 31, 2012 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Jun. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss) [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2012 Accumulated Net Unrealized Investment Gain (Loss) [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss) [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2012 Accumulated Net Unrealized Investment Gain (Loss) [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	Dec. 31, 2012 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	Jun. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2012 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2012 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Jun. 30, 2013 Other comprehensive income loss before reclassifications [Member] Accumulated Net Unrealized Investment Gain (Loss) [Member]	Jun. 30, 2013 Other comprehensive income loss before reclassifications [Member] Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense)	$ (10,428)	$ 2,950	$ (24,885)	$ 18,094							$ 0	$ (700)	$ 4,300	$ (800)
Income tax expense	159,140	121,021	224,648	203,169					5,400	2,500	0	300	(1,500)	300	400	1,100	(200)	(1,300)	(300)	(1,900)	4,400	1,800
Revenues	1,723,473	1,420,951	3,138,569	2,712,966													100	13,600	1,200	19,000
Net income	$ 490,670	$ 387,141	$ 917,419	$ 689,507	$ (100)	$ 11,900	$ 3,700	$ 16,600