Marketable Securities - Maturities of Debt Securities Classified as Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Marketable Securities
Fair Value, Due within one year	$ 47,046	$ 89,477
Fair Value, Due after one year through five years	5,000	22,031
Fair Value	52,046	111,508
Net Carrying Amount, Due within one year	47,286	89,728
Net Carrying Amount, Due after one year through five years	5,000	22,149
Net Carrying Amount	$ 52,286	$ 111,877