Short-Term Investments

9 Months Ended

Sep. 30, 2019

5. Short-Term Investments

The following is a summary of our short-term investments (in thousands):

	September 30, 2019
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
	Cost		Gains		Losses		Fair Value
U.S. treasury bills and government agency obligations	$	69,702	$	57	$	—	$	69,759
U.S. corporate debt securities		29,078		23		—		29,101
Foreign corporate debt securities		10,670		18		—		10,688
U.S. commercial paper		32,363		5		—		32,368
Foreign commercial paper		54,254		—		—		54,254
Total	$	196,067	$	103	$	—	$	196,170

	December 31, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
U.S. treasury bills and government agency obligations	$	59,747	$	—	$	(6	)	$	59,741
U.S. corporate debt securities		59,164		—		(77	)		59,087
Foreign corporate debt securities		5,041		5		—			5,046
U.S. commercial paper		52,800		—		—			52,800
Foreign commercial paper		123,870		—		(9	)		123,861
Total	$	300,622	$	5	$	(92	)	$	300,535

The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. We regularly monitor and evaluate the realizable value of our marketable securities. We did not recognize any impairment losses during the three and nine months ended September 30, 2019 and 2018.

Realized gains and losses associated with our investments, if any, are reported in the statements of operations and comprehensive loss. We did not recognize any realized gains or losses during the three months ended September 30, 2019 and 2018. We recognized $8,000 in realized gains during the nine months ended September 30, 2019. We did not recognize any realized gains or losses during the nine months ended September 30, 2018.