Cash Equivalents and Investments (Tables)

12 Months Ended

Dec. 31, 2017

Cash and Cash Equivalents [Abstract]

Summary of cash and available-for-sale securities

The following tables summarize the Company’s cash and available-for-sale securities’ amortized cost, gross unrealized gains, gross unrealized losses, and fair value by significant investment category reported as cash and cash equivalents, or short-term investments as of December 31, 2017 and 2016:

							Reported as:
Summary of Cash and Available-For-Sale Securities (in thousands)	Adjusted Cost		Unrealized Gains		Fair Value		Cash and Cash Equivalents		Short-Term Investments
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
December 31, 2016
Cash	$	147,150	$	—	$	147,150	$	147,150	$	—
Money market funds	4		—		4		4		—
Commercial paper	19,987		—		19,987		—		19,987
Total	$	167,141	$	—	$	167,141	$	147,154	$	19,987