Investments, Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gain (Loss) on Securities [Line Items]
Change in unrealized gains (losses)	$ 220,139	$ (81,834)	$ 69,052
Available-for-Sale Securities | Fixed income
Gain (Loss) on Securities [Line Items]
Change in unrealized gains (losses)	220,139	(81,834)	69,026
Available-for-Sale Securities | Equity Securities
Gain (Loss) on Securities [Line Items]
Change in unrealized gains (losses)	0	0	39
Available-for-Sale Securities | Other
Gain (Loss) on Securities [Line Items]
Change in unrealized gains (losses)	$ 0	$ 0	$ (13)