Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Summary of the Levels of the Fair Value Hierarchy into Which the Company's Financial Assets Fall

The following table summarizes the levels of the fair value hierarchy into which the Company’s financial assets fall as of June 30, 2018:

	Total		Level 1			Level 2			Level 3
Financial assets:
Included in cash and cash equivalents
U.S. treasury instruments		71,910			14,977			56,933		—
Government securities money market		18,115		—				18,115		—
Investments
Government debt securities (1)		5,321			—			5,321			—
U.S. treasury instruments		53,000			53,000			—		—
Common stock		290			290		—				—
Total financial assets	$	148,636	$		68,267	$		80,369	$		—

(1) Consists of municipal bonds, agency bonds and agency discount notes.

The following table summarizes the levels of the fair value hierarchy into which the Company’s financial assets fall as of December 31, 2017:

	Total		Level 1			Level 2			Level 3
Financial assets:
Included in cash and cash equivalents
Government debt securities (1)	$	41,086	$		—	$		41,086	$	—
U.S. treasury instruments		39,978		—				39,978		—
Government securities money market		46,095		—				46,095			—
Investments
Government debt securities (1)		39,910			—			39,910		—
U.S. treasury instruments		55,935			7,943			47,992			—
Common stock		263			263		—				—
Total financial assets	$	223,267	$		8,206	$		215,061	$		—

(1) Consists of municipal bonds, agency bonds and agency discount notes