Investments - Schedule of Available-For-Sale Investment Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
Due in less than 1 year	$ 55,801	$ 45,391
Due in 1-5 years	25,040	13,204
Total	80,841	58,595
Fair Value
Due in less than 1 year	55,735	45,344
Due in 1-5 years	24,913	13,175
Total	$ 80,648	$ 58,519