Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Schedule of Marketable Securities

Our investments in marketable securities are classified as available for sale and are summarized as follows (in thousands):

	June 30, 2019
	Amortized Cost		Unrealized Gain		Market Value
U.S. Treasury bills (due within one year)	$	149,935	$	10	$	149,945

	December 31, 2018
	Amortized Cost		Unrealized Gain		Market Value
U.S. Treasury bills (due within one year)	$	299,813	$	36	$	299,849