Reinsurance (Reinsurance Recoverable by Counterparty) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	$ 31,696,534	$ 32,555,500
PAR U
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	11,096,056	11,111,272
PALAC
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	7,343,099	8,388,988
PURC
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	3,700,711	3,577,962
PARCC
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	2,535,700	2,546,673
GUL Re
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	1,845,549	1,772,950
PAR Term
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	1,583,047	1,559,618
Prudential of Taiwan
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	1,451,312	1,406,686
Term Re
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	1,053,052	966,509
Prudential Insurance
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	1,039,039	1,152,241
DART
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	36,658	0
Unaffiliated
Effects of Reinsurance [Line Items]
Total reinsurance recoverables	$ 12,311	$ 72,601