Available-for-Sale Securities - Additional Information (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Available-for-sale securities investments, gross unrealized losses	$ 0						$ 0		$ 2,308
Unrealized gain on short and long-term investments	$ (1,864)	$ 819	$ 3,353	$ 2,457	$ (188)	$ (11,151)	2,308	$ (8,882)
Other-than-temporary impairment							$ 0