Summary of Investments - SOI Fixed Maturity AFS aging (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized cost
Maturing in one year or less	$ 796,697
Maturing after one year through five years	3,998,273
Maturing after five years through ten years	7,432,248
Maturing after ten years	5,000,632
Mortgage-backed and asset-backed securities	4,898,098
Amortized cost	22,125,948	$ 21,672,727
Estimated fair value
Maturing in one year or less	814,539
Maturing after one year through five years	4,166,545
Maturing after five years through ten years	7,650,580
Maturing after ten years	5,356,030
Mortgage-backed and asset-backed securities	5,025,175
Estimated fair value	$ 23,012,869	$ 22,153,703