Significant Accounting Policies and Pronouncements (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019	[1]	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Commercial mortgage and other loans, Loan-to- value ratios (greater than)	100.00%
Commercial mortgage and other loans, Loan-to-value ratios (less than)	100.00%
Commercial mortgage and other loans, Debt service coverage ratios (less than)	1.0
Commercial mortgage and other loans, Debt service coverage ratios (greater than)	1.0
Uncertain tax positions measurement percentage (greater than)	50.00%
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings / (accumulated deficit)	$ (46,693)	$ 943,005
Accumulated other comprehensive income (loss)	$ 428,612	(324,373)
Cumulative effect of adoption		$ 42
Securities Loaned Transactions Collateral Fair Value of Domestic Securities	102.00%
Securities Loaned Transactions Collateral Fair Value of Foreign Securities	105.00%
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Repurchase and Resale Agreements, Collateral, Percentage	95.00%
Insurance revenue and expense recognition, Assumed interest rate	0.00%	0.00%
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Insurance revenue and expense recognition, Assumed interest rate	8.30%	8.30%
Accumulated Other Comprehensive Income (loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income (loss)	$ 428,612	$ (324,373)				$ (90,124)	$ (314,948)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	428,612	(324,373)				(90,124)	(314,948)
Cumulative effect of adoption			$ 0		$ (36,700)
Accumulated Other Comprehensive Income (loss) | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption		(3)			(3)
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ (46,693)	$ 943,005				$ (776,762)	$ (693,258)
Cumulative effect of adoption			$ (371)		36,700
Retained earnings | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption					337
Restatement Adjustment | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings / (accumulated deficit)					337
Accumulated other comprehensive income (loss)					(3)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest					$ 334

[1] Includes the impact from the adoption of ASUs 2017-08 and 2017-12. See Note 2.