Derivatives - Income Statement (Details) - Derivatives not designated as hedges [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	$ (67,590)	$ (37,037)	$ 6,004
Included in net foreign exchange gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	(32,689)	38,589	(64,183)
Included in net realized and unrealized investment gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	(34,901)	(75,626)	70,187
Foreign exchange forward contracts [Member] | Included in net foreign exchange gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	(29,217)	39,399	(59,019)
Foreign currency option contracts [Member] | Included in net foreign exchange gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	(3,472)	(810)	(5,164)
Futures contracts [Member] | Included in net realized and unrealized investment gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	(32,004)	(72,146)	78,841
Insurance-linked securities [Member] | Included in net realized and unrealized investment gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	(1,556)	230	(707)
Total return swaps [Member] | Included in net realized and unrealized investment gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	1,390	(1,002)	(6,597)
Interest rate swaps [Member] | Included in net realized and unrealized investment gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	(8,101)	(15,871)	7,469
TBAs [Member] | Included in net realized and unrealized investment gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	2,877	13,166	(8,808)
Other [Member] | Included in net realized and unrealized investment gains and losses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized in income	$ 2,493	$ (3)	$ (11)