Investments - Schedule of Contractual Maturities of Available-for-Sale and Held-to-Maturity Securities (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Available-for-sale, Amortized Cost
Within 1 year	$ 213,318
After 1 year through 5 years	182,610
Amortized Cost	395,928
Available-for-sale, Estimated Fair Value
Within 1 year	213,172
After 1 year through 5 years	183,138
Total	396,310
Held-to-maturity, Amortized Cost
Within 1 year	1,820
After 1 year through 5 years	1,667
Total	3,487
Held-to-maturity, Estimated Fair Value
Within 1 year	1,820
After 1 year through 5 years	1,769
Total	$ 3,589