FAIR VALUE MEASUREMENT AND FINANCIAL INSTRUMENTS - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Liabilities:
Contingent consideration				$ 48,400
Significant Unobservable Inputs (Level 3)
Liabilities:
Contingent consideration	$ 95,000	$ 91,400	$ 47,400
Carrying Amount
Assets:
Money market funds (cash equivalents)	30,995			40,365
Liabilities:
Contingent consideration	95,000			48,400
Fair Value | Recurring
Assets:
Money market funds (cash equivalents)	30,995			40,365
Liabilities:
Contingent consideration	95,000			48,400
Fair Value | Recurring | Quoted Prices in Active Markets (Level 1)
Assets:
Money market funds (cash equivalents)	30,995			40,365
Liabilities:
Contingent consideration	0			0
Fair Value | Recurring | Significant other Observable Inputs (Level 2)
Assets:
Money market funds (cash equivalents)	0			0
Liabilities:
Contingent consideration	0			0
Fair Value | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Money market funds (cash equivalents)	0			0
Liabilities:
Contingent consideration	$ 95,000			$ 48,400