Investments (Cumulative Noncredit Portion of Other Than Temporary Impairment Recognized in Other Comprehensive Income and Change in Fair Value Since Other Than Temporary Impairment) (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Investment Holdings [Line Items]
Amortized cost	$ 248,456
OTTI recognized in other comprehensive income (loss)	(149,146)
Change in fair value since OTTI was recognized	181,705
Fair value	281,015
Corporate Securities
Investment Holdings [Line Items]
Amortized cost	50,755
OTTI recognized in other comprehensive income (loss)	(3,700)
Change in fair value since OTTI was recognized	9,268
Fair value	56,323
Residential Mortgage Backed Securities
Investment Holdings [Line Items]
Amortized cost	183,948
OTTI recognized in other comprehensive income (loss)	(145,446)
Change in fair value since OTTI was recognized	172,577
Fair value	211,079
Commercial Mortgage Backed Securities
Investment Holdings [Line Items]
Amortized cost	12,776
OTTI recognized in other comprehensive income (loss)	0
Change in fair value since OTTI was recognized	(401)
Fair value	12,375
Other Asset Backed Securities
Investment Holdings [Line Items]
Amortized cost	977
OTTI recognized in other comprehensive income (loss)	0
Change in fair value since OTTI was recognized	261
Fair value	$ 1,238