Investments

3 Months Ended

Mar. 31, 2016

Investments, Debt and Equity Securities [Abstract]

Investments

Investments

We invest our excess cash in commercial paper and debt instruments of financial institutions and corporations. As of March 31, 2016, 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 March 31, 2016
Corporate debt securities	2 or less	$	70,394	$	20	$	(49	)	$	70,365
Certificates of deposit	2 or less	11,240		—		—			11,240
Commercial paper	1 or less	4,235		9		—			4,244
Total		$	85,869	$	29	$	(49	)	$	85,849

	Maturity (in years)	Amortized cost		Unrealized					Estimated fair value
				Gains		Losses
As of December 31, 2015
Corporate debt securities	2 or less	$	81,054	$	16	$	(103	)	$	80,967
Certificates of deposit	2 or less	13,640		—		—			13,640
Commercial paper	1 or less	3,490		6		—			3,496
Total		$	98,184	$	22	$	(103	)	$	98,103