FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2016

FAIR VALUE MEASUREMENTS

Summary of the levels of the fair value hierarchy into which the Company's financial assets fall

The following tables summarize the levels of the fair value hierarchy into which the Company’s financial assets and liabilities fall as of December 31, 2016:

	Total		Level 1		Level 2		Level 3
Financial assets:
Included in cash and cash equivalents
U.S. treasury bills	$	44,999	$	—	$	44,999	$	—
Government securities money market		201,934		—		201,934		—
Investments
U.S. treasury bills		32,995		—		32,995		—
Common stock		388		388		—		—
Total financial assets	$	280,316	$	388	$	279,928	$	—

The following table summarizes the levels of the fair value hierarchy into which the Company’s financial assets fall as of December 31, 2015:

	Total		Level 1		Level 2		Level 3
Financial assets:
Included in cash and cash equivalents
U.S. treasury bills	$	100,996	$	71,998	$	28,998	$	—
Government securities money market		77,876		—		77,876		—
Investments
U.S. treasury bills		37,989		19,990		17,999		—
Convertible notes		635		—		—		635
Total financial assets	$	217,496	$	91,988	$	124,873	$	635

Schedule of changes to the Company's investment classified as Level 3

	Convertible notes
January 1, 2016	$	635
Unrealized gains (losses) included in accumulated other comprehensive income		43
Transfer out of level 3 due to conversion of convertible notes to common stock		(678)
December 31, 2016	$	—
Unrealized gains (losses) related to investment still held as of December 31, 2016	$	—

	Convertible notes
January 1, 2015	$	—
Non-cash settlement of customer receivable		635
December 31, 2015	$	635
Unrealized gains (losses) related to investment still held as of December 31, 2015	$	—