Investments - Analysis of net realized gains (losses) and the change in unrealized (losses) gains on investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Realized investment gains (losses):
OTTI on investments, net of amounts transferred to other comprehensive income	$ (1,806)	$ (6,874)
Total realized investment gains (losses)	(83,355)	37,286
Excluding Life Funds Withheld Assets
Realized investment gains (losses):
Gross realized gains	19,330	39,397	[1]
Gross realized losses	(51,002)	(28,305)	[1]
OTTI on investments, net of amounts transferred to other comprehensive income	(1,806)	(6,874)	[1]
Total realized investment gains (losses)	(33,478)	4,218	[1]
Equity Securities, FV-NI, Realized Gain	9,693	0
Equity Securities, FV-NI, Realized Loss	(126)	0
Equity Securities, FV-NI, Unrealized Gain (Loss)	(45,581)	0
Net realized and change in net unrealized gains (losses) on equity securities	(36,014)	0
Other Investments, FV-NI, Realized Gain	3,004	0
Other Investments, FV-NI, Realized Loss	(1,163)	0
Other Investments, FV-NI, Unrealized Gain (Loss)	6,808	0
Net realized and change in net unrealized gains (losses) on other investments	8,649	0
Life Funds Withheld Assets
Realized investment gains (losses):
Gross realized gains	12,909	35,151
Gross realized losses	(2,551)	(677)
OTTI on investments, net of amounts transferred to other comprehensive income	(1,203)	0
Change in net unrealized gains (losses) on trading securities	(31,667)	(1,406)
Total realized investment gains (losses)	$ (22,512)	$ 33,068

[1] AFS in the prior year includes net realized gains (losses) on equity securities and other investments. Due to the implementation of ASU 2016-01, as described in in Note 1(b), "Significant Accounting Policies - Recent Accounting Pronouncements," the net realized gains (losses) on these investments are shown separately.