Fair Value (Unobservable Input Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net Embedded Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	$ 403,037	$ 360,381
Total realized/unrealized gains (losses) included in net income (loss)	(131,329)	49,158
Total realized/unrealized gains (losses) included in AOCI	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	119,116	(5,711)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at March 31,	390,824	403,828
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at March 31, 2016 (7)	(130,943)	51,199
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at March 31, 2016 (7)	(130,943)	51,199
U.S. corporate and foreign corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	72,291	55,189
Total realized/unrealized gains (losses) included in net income (loss)	(42)	(896)
Total realized/unrealized gains (losses) included in AOCI	998	1,189
Purchases	20,631	2,369
Sales	(11,274)	(121)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	2,921
Transfers out of Level 3	0	(1,864)
Balance at March 31,	82,604	58,787
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at March 31, 2016 (7)	(42)	(896)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at March 31, 2016 (7)	(42)	(896)
Structured
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	31,423	13,862
Total realized/unrealized gains (losses) included in net income (loss)	95	56
Total realized/unrealized gains (losses) included in AOCI	216	(91)
Purchases	0	21
Sales	(1,449)	(418)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	42	0
Transfers out of Level 3	0	0
Balance at March 31,	30,327	13,430
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at March 31, 2016 (7)	95	56
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at March 31, 2016 (7)	$ 95	$ 56