Investments (Trading Account Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account assets, at amortized cost or cost	$ 172,705	$ 154,608
Trading account assets, at fair value	178,647	149,871
Fixed maturities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account assets, at amortized cost or cost	161,385	147,057
Trading account assets, at fair value	162,811	139,513
Equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account assets, at amortized cost or cost	11,320	7,551
Trading account assets, at fair value	$ 15,836	$ 10,358