MARKETABLE SECURITIES - Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	$ 208,257	$ 79,151
Less Than 12 Months, Unrealized Losses	1,750	65
12 Months or Greater, Fair Value	0	7,509
12 Months or Greater, Unrealized Losses	0	2
Total, Fair Value	208,257	86,660
Total, Unrealized Losses	1,750	67
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	4,981	0
Less Than 12 Months, Unrealized Losses	10	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	4,981	0
Total, Unrealized Losses	10	0
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	203,276	74,151
Less Than 12 Months, Unrealized Losses	1,740	64
12 Months or Greater, Fair Value		7,509
12 Months or Greater, Unrealized Losses		2
Total, Fair Value	203,276	81,660
Total, Unrealized Losses	1,740	66
Securities of government-sponsored entities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	0	5,000
Less Than 12 Months, Unrealized Losses	0	1
12 Months or Greater, Fair Value		0
12 Months or Greater, Unrealized Losses		0
Total, Fair Value	0	5,000
Total, Unrealized Losses	$ 0	$ 1