Fair Value Measurements Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 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:

	June 30, 2021						December 31, 2020
(in thousands)	Total		Level 1		Level 2		Total		Level 1		Level 2
Money market funds	$	435,014	$	435,014	$	—	$	551,213	$	551,213	$	—
U.S. Treasury bills	12,318		12,318		—		10,531		10,531		—
Municipal bonds	22,279		—		22,279		23,998		—		23,998
Total	$	469,611	$	447,332	$	22,279	$	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
June 30, 2021
U.S. Treasury bills	$	12,318	$	—	$	—	$	12,318
Municipal bonds	22,281		1		(3)		22,279
Total	$	34,599	$	1	$	(3)	$	34,597
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 June 30, 2021, the contractual maturities of our marketable securities were as follows:

(in thousands)	Amortized Cost		Estimated Fair Value
Less than one year	$	29,469	$	29,468
One to five years	5,130		5,129
Total	$	34,599	$	34,597