Fair Value Measurements Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

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

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

	Fair Value Measurements
	(in thousands)
	March 31, 2018		Level 1		Level 2		Level 3
Money market funds	$	327,816	$	327,816	$	—	$	—
Municipal bonds	1,928		—		1,928		—
Total	$	329,744	$	327,816	$	1,928	$	—

	Fair Value Measurements
	(in thousands)
	December 31, 2017		Level 1		Level 2		Level 3
Money market funds	$	360,746	$	360,746	$	—	$	—
Municipal bonds	1,960		—		1,960		—
Total	$	362,706	$	360,746	$	1,960	$	—