Fair Value Measurements Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block]

The following table summarizes the levels of fair value measurements of our financial assets:

	September 30, 2019						December 31, 2018
(in thousands)	Total		Level 1		Level 2		Total		Level 1		Level 2
Money market funds	$	232,777	$	232,777	$	—	$	325,819	$	325,819	$	—
U.S. Treasury bills	61,529		61,529		—		52,197		52,197		—
Municipal bonds	—		—		—		10,634		—		10,634
Total	$	294,306	$	294,306	$	—	$	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
September 30, 2019
U.S. Treasury bills	$	60,854	$	27	$	(1	)	$	60,880
Municipal bonds	—		—		—			—
Total	$	60,854	$	27	$	(1	)	$	60,880
December 31, 2018
U.S. Treasury bills	$	50,150	$	—	$	(3	)	$	50,147
Municipal bonds	10,640		1		(7		)	10,634
Total	$	60,790	$	1	$	(10	)	$	60,781

Investments Classified by Contractual Maturity Date [Table Text Block]

As of September 30, 2019, the contractual maturities of our marketable securities were as follows:

(in thousands)	Amortized Cost		Estimated Fair Value
Less than one year	$	60,854	$	60,880
One to five years	—		—
Total	$	60,854	$	60,880