Investments - Schedule of Contract Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Cost or Amortized Cost
One year or less	$ 100,713
After one year through five years	246,589
After five years through ten years	184,543
After ten years	120,929
Residential mortgage-backed	139,809
Commercial mortgage and asset-backed	178,248
Redeemable preferred stock	2,025
Total	972,856	$ 940,212
Fair Value
One year or less	100,916
After one year through five years	248,690
After five years through ten years	185,759
After ten years	127,448
Residential mortgage-backed	138,483
Commercial mortgage and asset-backed	178,749
Redeemable preferred stock	2,088
Total	$ 982,133	$ 941,077