Fair Value Measurements Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2020

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, 2020						December 31, 2019
(in thousands)	Total		Level 1		Level 2		Total		Level 1		Level 2
Money market funds	$	439,496	$	439,496	$	—	$	363,075	$	363,075	$	—
U.S. Treasury bills	11,197		11,197		—		34,728		34,728		—
Municipal bonds	23,205		—		23,205		—		—		—
Total	$	473,898	$	450,693	$	23,205	$	397,803	$	397,803	$	—

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, 2020
U.S. Treasury bills	$	11,170	$	27	$	—	$	11,197
Municipal bonds	20,700		56		(1)		20,755
Total	$	31,870	$	83	$	(1)	$	31,952
December 31, 2019
U.S. Treasury bills	$	34,716	$	13	$	(1)	$	34,728
Total	$	34,716	$	13	$	(1)	$	34,728

Investments Classified by Contractual Maturity Date [Table Text Block]

As of June 30, 2020, the contractual maturities of our marketable securities were as follows:

(in thousands)	Amortized Cost		Estimated Fair Value
Less than one year	$	31,870	$	31,952
One to five years	—		—
Total	$	31,870	$	31,952