Marketable Securities - Maturities of Debt Securities Classified as Available-for-Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Fair value, due within one year	$ 21,745
Fair value, due after one year through five years	5,000
Fair value	26,745	$ 111,508
Net carrying amount, due within one year	21,860
Net carrying amount, due after one year through five years	5,009
Net carrying amount	$ 26,869