Investments - Schedule of Available-for-Sale Investment Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized Cost
Due in less than 1 year	$ 60,999	$ 45,391
Due in 1-5 years	25,970	13,204
Total	86,969	58,595
Fair Value
Due in less than 1 year	60,974	45,344
Due in 1-5 years	25,915	13,175
Total	$ 86,889	$ 58,519