Fair Value Measurements Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Marketable Securities [Table Text Block]

Fair Value of Instruments Measured and Recognized at Fair Value

The following tables summarize the levels of fair value measurements of our financial assets:

	December 31, 2019						December 31, 2018
(in thousands)	Total		Level 1		Level 2		Total		Level 1		Level 2
Money market funds	$	363,075	$	363,075	$	—	$	325,819	$	325,819	$	—
U.S. Treasury bills	34,728		34,728		—		52,197		52,197		—
Municipal bonds	—		—		—		10,634		—		10,634
Total	$	397,803	$	397,803	$	—	$	388,650	$	378,016	$	10,634

Available-for-sale Securities [Table Text Block]

The following is a summary of our available-for-sale marketable securities:

(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
December 31, 2019
U.S. Treasury bills	$	34,716	$	13	$	(1	)	$	34,728
December 31, 2018
U.S. Treasury bills	$	50,150	$	—	$	(3	)	$	50,147
Municipal bonds	10,640		1		(7		)	10,634