Investment Information - Other than temporary impairments recognized in earnings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (1,730)	$ (5,343)	$ (3,537)	$ (12,982)
Fixed maturities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(1,666)	(3,408)	(3,184)	(8,948)
Fixed maturities | Mortgage backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(92)	(82)	(1,411)	(555)
Fixed maturities | Corporate bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(1,401)	(775)	(1,402)	(5,655)
Fixed maturities | Non-US government securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	0	(51)	(198)	(232)
Fixed maturities | Municipal bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	(173)	0
Fixed maturities | Asset backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	0	(2,500)	0	(2,506)
Equity securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	0	(1,935)	(186)	(3,037)
Other investments
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses recognized in earnings	$ (64)	$ 0	$ (167)	$ (997)