Short-term Investments - Summary of Investments in a Continuous Loss Position (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair value	$ 42,304
Less Than 12 Months, Gross unrealized losses	(54)
12 Months or Greater, Fair value	0
12 Months or Greater, Gross unrealized losses	0
Total, Fair value	42,304
Total, Gross unrealized losses	(54)
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair value	19,965
Less Than 12 Months, Gross unrealized losses	(19)
12 Months or Greater, Fair value	0
12 Months or Greater, Gross unrealized losses	0
Total, Fair value	19,965
Total, Gross unrealized losses	(19)
U.S. government-related debt securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair value	17,883
Less Than 12 Months, Gross unrealized losses	(34)
12 Months or Greater, Fair value	0
12 Months or Greater, Gross unrealized losses	0
Total, Fair value	17,883
Total, Gross unrealized losses	(34)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair value	4,456
Less Than 12 Months, Gross unrealized losses	(1)
12 Months or Greater, Fair value	0
12 Months or Greater, Gross unrealized losses	0
Total, Fair value	4,456
Total, Gross unrealized losses	$ (1)