FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair value, measurements, recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets:
Cash equivalents	$ 13,732	$ 71,568
Total Assets	72,474	212,483
Liabilities:
Total Liabilities	17	359
Other
Liabilities:
Contingent consideration	17	359
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	13,732	71,568
Total Assets	13,732	71,568
Liabilities:
Total Liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Liabilities:
Contingent consideration	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Total Assets	58,742	140,915
Liabilities:
Total Liabilities	0	0
Significant Other Observable Inputs (Level 2) | Other
Liabilities:
Contingent consideration	0	0
Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Total Assets	0	0
Liabilities:
Total Liabilities	17	359
Significant Unobservable Inputs (Level 3) | Other
Liabilities:
Contingent consideration	17	359
Corporate debt securities
Assets:
Available-for-sale securities	54,492	113,097
Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities	0	0
Corporate debt securities | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	54,492	113,097
Corporate debt securities | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities	0	0
U.S. treasury and government agency securities
Assets:
Available-for-sale securities	2,750	10,323
U.S. treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities	0	0
U.S. treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	2,750	10,323
U.S. treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities	0	0
Commercial paper
Assets:
Available-for-sale securities		3,995
Commercial paper | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities		0
Commercial paper | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities		3,995
Commercial paper | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities		0
Certificates of deposit
Assets:
Available-for-sale securities	1,500	13,500
Certificates of deposit | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities	0	0
Certificates of deposit | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	1,500	13,500
Certificates of deposit | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities	$ 0	$ 0