Investments (Tables)

6 Months Ended

Jun. 30, 2019

Cash and Available-for-sale Securities by Significant Investment Category [Line Items]

Cash and Available-for-sale Securities by Significant Investment Category [Table Text Block]

The Company's cash, cash equivalents, and marketable securities by significant investment category are as follows:

	Fair Value								Balance Sheet Classification
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value		Cash and Cash Equivalents		Marketable Securities
Balance at June 30, 2019
Cash									$	78,982	$	—
Level 1(1):
Money market funds	5,518		—		—		5,518		5,518		—
U.S. Treasury securities	57,501		12		—		57,513		18,815		38,698
Total Level 1	63,019		12		—		63,031		24,333		38,698
Level 2(2):
Commercial paper	1,999		—		—		1,999		1,999		—
Total	$	65,018	$	12	$	—	$	65,030	$	105,314	$	38,698

	Fair Value								Balance Sheet Classification
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value		Cash and Cash Equivalents		Marketable Securities
Balance at December 31, 2018
Cash									$	279,829	$	—
Level 1(1):
Money market funds	77		—		—		77		77		—
Total	$	77	$	—	$	—	$	77	$	279,906	$	—

(1) Level 1 – Quoted prices in active markets for identical assets and liabilities.

(2) Level 2 – Quoted prices in active markets for similar assets and liabilities, or other inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument.