Summary of Investments - SOI AFS Proceeds from sales (Details 2.1) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 891,026	$ 1,673,307	$ 2,471,548	$ 3,356,200
Gross realized gains from sales	8,488	26,810	20,921	46,667
Gross realized losses from sales	$ 6,080	$ 135	$ 21,337	$ 146