Investments (Schedule of Other Than Temporary Impairment Losses, Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Amortized cost	$ 352,207	$ 315,164
OTTI recognized in other comprehensive income (loss)	(171,546)	(173,974)
Change in fair value since OTTI was recognized	205,712	210,484
Fair value	386,373	351,674
Corporate Securities
Investment Holdings [Line Items]
Amortized cost	69,580	13,015
OTTI recognized in other comprehensive income (loss)	(3,700)	(4,263)
Change in fair value since OTTI was recognized	6,195	10,739
Fair value	72,075	19,491
Residential Mortgage Backed Securities
Investment Holdings [Line Items]
Amortized cost	245,691	297,582
OTTI recognized in other comprehensive income (loss)	(167,846)	(168,355)
Change in fair value since OTTI was recognized	199,191	201,620
Fair value	277,036	330,847
Commercial Mortgage Backed Securities
Investment Holdings [Line Items]
Amortized cost	35,244
OTTI recognized in other comprehensive income (loss)	0
Change in fair value since OTTI was recognized	0
Fair value	35,244
Other Asset Backed Securities
Investment Holdings [Line Items]
Amortized cost	1,692	4,567
OTTI recognized in other comprehensive income (loss)	0	(1,356)
Change in fair value since OTTI was recognized	326	(1,875)
Fair value	$ 2,018	$ 1,336