INVESTMENTS IN DEBT SECURITIES - Contractual Maturities of Short-Term and Long-Term Investments (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Amortized Cost
Due in one year or less	$ 520,017
Due in one to five years	528,798
Amortized Cost	1,048,815
Fair Value
Due in one year or less	521,840
Due in one to five years	529,460
Fair Value	$ 1,051,300