Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Table Text Blocks

Schedule of assets measured at fair value on a recurring basis

	Quoted Price
	in Active	Significant
	Market for	Other	Significant
	Identical	Observable	Unobservable
	Assets	Inputs	Inputs
As of June 30, 2018	(Level 1)	(Level 2)	(Level 3)
	$	$	$
Short-term investment (Note 5):
U.S. treasury securities	903,415	—	—
U.S. agency securities	17,621	—	—
Time deposits	10,172	—	—
Cash equivalents
U.S. treasury securities	9,988	—	—
Money market funds	127,423	—	—
Total	1,068,619	—	—

	Quoted Price
	in Active	Significant
	Market for	Other	Significant
	Identical	Observable	Unobservable
	Assets	Inputs	Inputs
As of December 31, 2017	(Level 1)	(Level 2)	(Level 3)
	$	$	$
Short-term investment (Note 5):
U.S. treasury securities	561,327	—	—
U.S. agency securities	17,663	—	—
Time deposits	18,924	—	—
Cash equivalents
Money market funds	44,730	—	—
Total	642,644	—	—