Financial Instruments - Additional Information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Remaining contractual maturities of available-for-sale-securities	less than one year
Realized gains (losses) on available-for-sale securities	$ 0
Unrealized losses on cash equivalents and investments	2,000
Gross unrealized loss in continuous loss position for 12 months or longer	0	$ 59,000
Cash, cash equivalents, restricted cash and short term investments	134,000,000
Cash portion included in cash, cash equivalents, restricted cash and investments	700,000
Cash equivalents, restricted cash and investments	$ 133,300,000