DEBT SECURITIES - Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	$ 101,240	$ 79,151
Less Than 12 Months, Unrealized Losses	13	65
12 Months or Greater, Fair Value	0	7,509
12 Months or Greater, Unrealized Losses	0	2
Total, Fair Value	101,240	86,660
Total, Unrealized Losses	13	67
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	58,166	0
Less Than 12 Months, Unrealized Losses	6	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	58,166	0
Total, Unrealized Losses	6	0
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	0	74,151
Less Than 12 Months, Unrealized Losses	0	64
12 Months or Greater, Fair Value	0	7,509
12 Months or Greater, Unrealized Losses	0	2
Total, Fair Value	0	81,660
Total, Unrealized Losses	0	66
Securities of government-sponsored entities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	43,074	5,000
Less Than 12 Months, Unrealized Losses	7	1
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	43,074	5,000
Total, Unrealized Losses	$ 7	$ 1