Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Measurements

Schedule of assets measured at fair value on a recurring basis

	Fair Value Measurements as of June 30, 2019
	Total		Level 1		Level 2		Level 3
Cash and cash equivalents	$	253,661	$	253,661	$	—	$	—
Marketable securities
Bonds and bond funds	$	200,281	$	—	$	200,281	$	—
Commercial paper		95,619		—		95,619		—
		295,900		—		295,900		—
Total assets measured at fair value	$	549,561	$	253,661	$	295,900	$	—

	Fair Value Measurements as of December 31, 2018
	Total		Level 1		Level 2		Level 3
Cash and cash equivalents	$	328,384	$	328,384	$	—	$	—
Marketable securities
Bonds and bond funds	$	229,783	$	—	$	229,783	$	—
Commercial paper		131,162		—		131,162		—
		360,945		—		360,945		—
Total assets measured at fair value	$	689,329	$	328,384	$	360,945	$	—