Investments - Credit loss impairments on fixed income securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
OTTI related to credit losses recognized in earnings
Balance, beginning of period	$ 73,469	$ 131,942
Credit loss impairment recognized in the current period on securities not previously impaired	12,867	9,698
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period	(18,178)	(54,648)
Credit loss impairments previously recognized on securities impaired to fair value during the period	0	(2,629)
Additional credit loss impairments recognized in the current period on securities previously impaired	2,233	2,230
Accretion of credit loss impairments previously recognized due to an increase in cash flows expected to be collected	(8,796)	(13,124)
Balance, end of period	$ 61,595	$ 73,469