Investments - Amortized Cost and Estimated Fair Value of Available-For-Sale Securities by Contractual Maturity (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Amortized cost
Due in one year or less	$ 24,154
Due after one year through five years	362,607
Due after five years through ten years	129,547
Due after ten years	276,162
Amortized cost	792,470
Estimated fair value
Due in one year or less	24,233
Due after one year through five years	372,299
Due after five years through ten years	128,334
Due after ten years	279,959
Estimated fair value	$ 804,825