Investments (Details 2) $ in Thousands	Mar. 31, 2018 USD ($)
Amortized cost
Due in one year or less	$ 96,656
Due after one year through five years	254,866
Due after five years through ten years	258,775
Due after ten years	122,321
Amortized cost, fixed maturities	732,618
Estimated fair value
Due in one year or less	96,574
Due after one year through five years	255,157
Due after five years through ten years	257,096
Due after ten years	120,977
Estimated fair value, fixed maturities	$ 729,804