Investments (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value	$ 5,818,116	$ 5,201,921
Percentage threshold that triggers a review of available for sale debt securities for declines in market value	80.00%
Aggregate market value of investments in unrealized loss position	2,064,732	1,657,025
Gross unrealized losses on investments in unrealized loss position	42,018	64,557
Percentage threshold of unrealized losses not exceeded by any one single issuer	0.70%	0.90%
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	19,164	44,870
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	22,854	19,687
Additional contractual commitments	227,589
Other invested assets, at fair value, shares	9,719,971
Percentage of shares representing the total outstanding shares	17.70%
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Limited partnership financial reporting lag time, months	1 month
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Limited partnership financial reporting lag time, months	3 months
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value	567,131
Aggregate market value of investments in unrealized loss position	127,522	130,158
Gross unrealized losses on investments in unrealized loss position	4,274	7,941
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	349	5,255
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	3,925	2,686
European Sovereign Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value	73,825
Percentage threshold maximum of securities held in sovereign debt	5.00%
France [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of securities held in sovereign debt of a specific country	52.90%
United Kingdom [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of securities held in sovereign debt of a specific country	16.80%
Netherlands [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of securities held in sovereign debt of a specific country	8.40%
Belgium [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of securities held in sovereign debt of a specific country	8.10%
Germany [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of securities held in sovereign debt of a specific country	5.40%
Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	3,452	38,527
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	21,240	18,867
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate market value of investments in unrealized loss position	2,064,732	1,657,012
Gross unrealized losses on investments in unrealized loss position	42,018	64,555
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	19,164	44,868
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	22,854	19,687
Sub-Prime And Alt-A Loans [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation		$ 33