Investments

6 Months Ended

Jun. 30, 2018

Debt Securities, Available-for-sale [Abstract]

Investments

Investments

We invest our excess cash primarily in debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. We generally hold our investments to maturity and do not sell our investments before we have recovered our amortized cost basis.

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, 2018
Corporate debt securities	1 or less	$	10,007	$	—	$	(7	)	$	10,000
Certificates of deposit	1 or less	3,890		—		—			3,890
U.S. Treasury securities	1 or less	3,998		—		(14		)	3,984
Debt securities of U.S. government-sponsored agencies	1 or less	1,499		—		(2		)	1,497
Total		$	19,394	$	—	$	(23	)	$	19,371

	Maturity (in years)	Amortized cost		Unrealized					Estimated fair value
				Gains		Losses
As of December 31, 2017
Corporate debt securities	1 or less	$	32,922	$	—	$	(55	)	$	32,867
Certificates of deposit	1 or less	8,216		—		—			8,216
U.S. Treasury securities	1 or less	3,996		—		(18		)	3,978
Debt securities of U.S. government-sponsored agencies	1 or less	1,498		—		(4		)	1,494
Total		$	46,632	$	—	$	(77	)	$	46,555