Marketable Securities (Tables)

3 Months Ended

Mar. 31, 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):

	March 31, 2019
	Amortized Cost		Unrealized Gain		Market Value
U.S. Treasury bills (due within one year)	$	249,842	$	16	$	249,858

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