Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2017

Fair Value Disclosures [Abstract]

Assets Measured or Disclosed at Fair Value on Recurring Basis

Assets measured or disclosed at fair value on a recurring basis as of June30, 2017 and December 31, 2016 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
June 30, 2017
Assets:
Cash and cash equivalents	$	125,390	$	—	$	—	$	125,390
Certificates of deposit		—		14,855		—		14,855
U.S. Government debt securities		—		128,226		—		128,226
Corporate debt securities		—		52,744		—		52,744
	$	125,390	$	195,825	$	—	$	321,215

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
December 31, 2016
Assets:
Cash and cash equivalents	$	187,335	$	—	$	—	$	187,335
Certificates of deposit		—		12,698		—		12,698
U.S. Government debt securities		—		50,920		—		50,920
Corporate debt securities		—		9,390		—		9,390
	$	187,335	$	73,008	$	—	$	260,343