FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Assets Measured and Carried at Fair Value

The tables below present information about the Company’s financial assets that are measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques it utilizes to determine such fair value: 

	Fair Value Measurement as of December 31, 2017
	Total		Level 1		Level 2		Level 3
	(in thousands)
Assets
Cash equivalents	$	352,370	$	352,370	$	—	$	—
Commercial paper		133,368		—		133,368		—
Government and government agency bonds		294,717		284,745		9,972		—
Corporate bonds		127,956		127,956		—		—
Certificates of deposit		648		648		—		—
Total assets	$	909,059	$	765,719	$	143,340	$	—
	Fair Value Measurement as of December 31, 2016
	Total		Level 1		Level 2		Level 3
	(in thousands)
Cash equivalents	$	1,147	$	1,147	$	—	$	—
Commercial paper		69,304		—		69,304		—
Government and government agency bonds		105,287		—		105,287		—
Corporate bonds		20,834		—		20,834		—
Certificates of deposit		11,343		11,343		—		—
Total assets	$	207,915	$	12,490	$	195,425	$	—