Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Accumulated Other Comprehensive Income Loss Net Of Tax [Line Items]
Balance, Beginning of Period					$ 2,108,902		$ 1,618,153
Other comprehensive income (loss) before reclassifications					(921,750)
Amounts reclassified from AOCI					(5,018)
Net current-period other comprehensive income (loss)	(794,606)		187,396		(926,768)		181,045
Change in component during the period							181,045
Balance, End of Period	1,182,134		1,799,198		1,182,134		1,799,198
Accumulated Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax [Line Items]
Balance, Beginning of Period					267,475		229,795
Other comprehensive income (loss) before reclassifications					(102,937)
Amounts reclassified from AOCI					0
Net current-period other comprehensive income (loss)					(102,937)
Change in component during the period							7,215
Balance, End of Period	164,538		237,010		164,538		237,010
Unrealized Appreciation Of Securities [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax [Line Items]
Balance, Beginning of Period					1,877,657	[1]	1,419,318	[1]
Other comprehensive income (loss) before reclassifications					(819,019)	[1]
Amounts reclassified from AOCI					(6,512)	[1]
Net current-period other comprehensive income (loss)					(825,531)	[1]
Change in component during the period							172,329	[1]
Balance, End of Period	1,052,126	[1]	1,591,647	[1]	1,052,126	[1]	1,591,647	[1]
Pension And Postretirement Benefits [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax [Line Items]
Balance, Beginning of Period					(36,230)		(30,960)
Other comprehensive income (loss) before reclassifications					206
Amounts reclassified from AOCI					1,494
Net current-period other comprehensive income (loss)					1,700
Change in component during the period							1,501
Balance, End of Period	$ (34,530)		$ (29,459)		$ (34,530)		$ (29,459)

[1] Includes cash flow hedges. See Note 5 - “Derivative Instruments” for additional information on cash flow hedges.