Short-term Investments (Tables)

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Schedule of Short-term Investments

The following tables summarize the Company's short-term investments (dollars in thousands):

		As of March 31, 2019
	Maturity	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
Corporate debt securities	1 year or less	$	91,173	$	75	$	(4	)	$	91,244
Commercial paper	1 year or less	114,219		44		(1		)	114,262
U.S. Treasury bills	1 year or less	18,881		5		—			18,886
Other sovereign securities	1 year or less	1,988		—		—			1,988
		$	226,261	$	124	$	(5	)	$	226,380

		As of December 31, 2018
	Maturity	Amortized cost		Gross unrealized gains		Gross unrealized losses			Estimated fair value
Corporate debt securities	1 year or less	$	111,933	$	26	$	(43	)	$	111,916
Commercial paper	1 year or less	74,433		—		(24		)	74,409
U.S. Treasury bills	1 year or less	3,771		—		—			3,771
		$	190,137	$	26	$	(67	)	$	190,096