- SOI Net investment income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net investment income
Investment income before expenses		$ 1,239,454	$ 1,295,541	$ 1,273,008
Investment expenses		(19,401)	(18,982)	(18,578)
Net investment income		1,220,053	1,276,559	1,254,430
Fixed maturity and short-term investments
Net investment income
Investment income before expenses		890,593	819,047	796,133
Mortgage loans on real estate
Net investment income
Investment income before expenses		163,361	142,478	150,284
Policy loans
Net investment income
Investment income before expenses		199,383	199,737	206,081
Limited partnership and other corporation interests
Net investment income
Investment income before expenses		1,812	1,759	10,462
Net interest on funds withheld balances under reinsurance agreements, related party
Net investment income
Investment income before expenses		21,813	22,045	22,165
Derivative instruments (1)
Net investment income
Investment income before expenses	[1]	(48,684)	100,007	78,655
Other
Net investment income
Investment income before expenses		$ 11,176	$ 10,468	$ 9,228

[1] Includes gains (losses) on the hedged asset for fair value hedges.