Investments - Analysis of net realized gains (losses) and the change in unrealized (losses) gains on investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Realized investment gains (losses):
OTTI on investments, net of amounts transferred to other comprehensive income	$ (3,000)	$ (1,210)	$ (4,806)	$ (8,084)
Total realized investment gains (losses)	90,805	56,628	7,450	93,914
Excluding Life Funds Withheld Assets
Realized investment gains (losses):
Gross realized gains	25,288	91,771	44,618	131,168	[1]
Gross realized losses	(39,388)	(41,392)	(90,390)	(69,697)	[1]
OTTI on investments, net of amounts transferred to other comprehensive income	(3,000)	(1,210)	(4,806)	(8,084)	[1]
Total realized investment gains (losses)	(17,100)	49,169	(50,578)	53,387	[1]
Equity Securities, FV-NI, Realized Gain	4,556	0	14,249	0
Equity Securities, FV-NI, Realized Loss	(97)	0	(223)	0
Equity Securities, FV-NI, Unrealized Gain (Loss)	30,735	0	(14,846)	0
Net realized and change in net unrealized gains (losses) on equity securities	35,194	0	(820)	0
Other Investments, FV-NI, Realized Gain	17,208	0	20,212	0
Other Investments, FV-NI, Realized Loss	(1,261)	0	(2,424)	0
Other Investments, FV-NI, Unrealized Gain (Loss)	(6,645)	0	163	0
Net realized and change in net unrealized gains (losses) on other investments	9,302	0	17,951	0
Life Funds Withheld Assets
Realized investment gains (losses):
Gross realized gains	67,749	30,100	80,658	65,251
Gross realized losses	(2,444)	(322)	(4,995)	(999)
OTTI on investments, net of amounts transferred to other comprehensive income	0	0	(1,203)	0
Change in net unrealized gains (losses) on trading securities	(1,896)	(22,319)	(33,563)	(23,725)
Total realized investment gains (losses)	$ 63,409	$ 7,459	$ 40,897	$ 40,527

[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 noted in Note 1(b), "Significant Accounting Policies - Recent Accounting Pronouncements," the movements on these investments are now shown separately.