Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended					12 Months Ended	3 Months Ended			12 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Reclassification out of Accumulated Other Comprehensive Income	Mar. 31, 2013 Reclassification out of Accumulated Other Comprehensive Income	Mar. 31, 2014 Accumulated Net Unrealized Investment Gain (Loss)	Dec. 31, 2013 Accumulated Net Unrealized Investment Gain (Loss)	Mar. 31, 2014 Accumulated Net Unrealized Investment Gain (Loss) Reclassification out of Accumulated Other Comprehensive Income	Mar. 31, 2013 Accumulated Net Unrealized Investment Gain (Loss) Reclassification out of Accumulated Other Comprehensive Income	Mar. 31, 2014 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges	Dec. 31, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges	Mar. 31, 2014 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Mar. 31, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Mar. 31, 2014 Other comprehensive income loss before reclassifications Accumulated Net Unrealized Investment Gain (Loss)	Mar. 31, 2013 Other comprehensive income loss before reclassifications Accumulated Net Unrealized Investment Gain (Loss)	Mar. 31, 2014 Other comprehensive income loss before reclassifications Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges	Mar. 31, 2013 Other comprehensive income loss before reclassifications Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense)	$ (5,601)	$ (14,457)					$ 100	$ 4,100
Income tax benefit (expense)	178,414	65,508			4,300	3,300	0	(1,400)	300	100	400	(100)	1,100	700	100	1,600
Revenues	2,129,751	1,415,096									(4,700)	1,100
Net income	$ 479,728	$ 426,749	$ (4,200)	$ 3,700