Derivative Instruments (Location and Amounts of Unrealized And Realized Gains (Losses) On Derivatives Recorded In The Condensed Consolidated Income Statements) (Details) (Not Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	$ (18,984)	$ (13,788)
Foreign exchange (loss) gain
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(7,352)	(868)
Foreign exchange (loss) gain | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(7,352)	(868)
Net realized investment gains
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	(11,632)	(12,920)
Net realized investment gains | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	1,050	(558)
Net realized investment gains | Interest rate futures
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses on derivatives	$ (12,682)	$ (12,362)