Summary of Investments - SOI Other-than-temporary impairment recognition (Details) - Total fixed maturity investments - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 83,665	$ 102,343	$ 119,532
Initial impairments - credit loss on securities not previously impaired	0	0	759
Due to sales, maturities, or payoffs during the period	0	(1,785)	(559)
Due to increases in cash flows expected to be collected that are recognized over the remaining life of the security	(21,434)	(16,893)	(17,389)
Ending balance	$ 62,231	$ 83,665	$ 102,343