Investments - Impairment Charges in Earnings on Available-for-sale Securities (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]
Impairment charges recognized in earnings	$ 484	$ 803	$ 695	$ 2,830
Equity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Impairment charges recognized in earnings	25	5	160	32
Investments in fixed-maturity securities not in default [Member] | Fixed-maturity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Impairment charges recognized in earnings	$ 459	683	$ 535	2,679
Investments in fixed-maturity securities in default [Member] | Fixed-maturity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Impairment charges recognized in earnings		$ 115		$ 119