Investments

9 Months Ended

Sep. 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 September 30, 2017, our short-term investments had a weighted average maturity of less than two years.

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

	Maturity (in years)	Amortized cost		Unrealized					Estimated fair value
				Gains		Losses
As of September 30, 2017
Corporate debt securities	1 or less	$	38,736	$	1	$	(30	)	$	38,707
Certificates of deposit	2 or less	6,450		—		—			6,450
U.S. Treasury securities	2 or less	4,502		—		(6		)	4,496
Debt securities of U.S. government-sponsored agencies	1 or less	1,497		—		(2		)	1,495
Total		$	51,185	$	1	$	(38	)	$	51,148

	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