Cash Equivalents and Investments (Tables)

9 Months Ended

Sep. 30, 2018

Cash and Cash Equivalents [Abstract]

Summary of cash and available-for-sale securities

							Reported as:
(in thousands)	Amortized Cost		Unrealized Gains		Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
September 30, 2018
Cash	$	175,471	$	—	$	175,471	$	175,471	$	—
Money market funds	225,513		—		225,513		225,513		—
Total	$	400,984	$	—	$	400,984	$	400,984	$	—
December 31, 2017
Cash	$	109,703	$	—	$	109,703	$	109,703	$	—
Money market funds	417,563		—		417,563		417,563		—
Corporate securities	3,353		1,495		4,848		—		4,848
Total	$	530,619	$	1,495	$	532,114	$	527,266	$	4,848