Investments

6 Months Ended

Jun. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Investments

Investments

We invest our excess cash primarily in commercial paper and debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. As of June 30, 2017, our short-term investments had a weighted average maturity of less than one year.

The following tables summarize our short-term investments (in thousands):

	Maturity (in years)	Amortized cost		Unrealized					Estimated fair value
				Gains		Losses
As of June 30, 2017
Corporate debt securities	1 or less	$	21,264	$	—	$	(9	)	$	21,255
Certificates of deposit	1 or less	3,785		—		—			3,785
U.S. Treasury securities	1 or less	2,010		—		(1		)	2,009
Debt securities of U.S. government-sponsored agencies	1 or less	500		—		—			500
Total		$	27,559	$	—	$	(10	)	$	27,549

	Maturity (in years)	Amortized cost		Unrealized					Estimated fair value
				Gains		Losses
As of December 31, 2016
Corporate debt securities	2 or less	$	49,185	$	12	$	(77	)	$	49,120
Certificates of deposit	1 or less	9,291		—		—			9,291
Commercial paper	1 or less	1,247		—		—			1,247
U.S. Treasury securities	1 or less	1,001		—		(1		)	1,000
Debt securities of U.S. government-sponsored agencies	1 or less	512		—		—			512
Total		$	61,236	$	12	$	(78	)	$	61,170