Fair Value Measurements Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2021

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:

	March 31, 2021						December 31, 2020
(in thousands)	Total		Level 1		Level 2		Total		Level 1		Level 2
Money market funds	$	480,885	$	480,885	$	—	$	551,213	$	551,213	$	—
U.S. Treasury bills	13,269		13,269		—		10,531		10,531		—
Municipal bonds	21,023		—		21,023		23,998		—		23,998
Total	$	515,177	$	494,154	$	21,023	$	585,742	$	561,744	$	23,998

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
March 31, 2021
U.S. Treasury bills	$	13,267	$	2	$	—	$	13,269
Municipal bonds	21,028		1		(6)		21,023
Total	$	34,295	$	3	$	(6)	$	34,292
December 31, 2020
U.S. Treasury bills	$	10,530	$	1	$	—	$	10,531
Municipal bonds	23,994		8		(4)		23,998
Total	$	34,524	$	9	$	(4)	$	34,529

Investments Classified by Contractual Maturity Date [Table Text Block]

As of March 31, 2021, the contractual maturities of our marketable securities were as follows:

(in thousands)	Amortized Cost		Estimated Fair Value
Less than one year	$	34,295	$	34,292
One to five years	—		—
Total	$	34,295	$	34,292