Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net change in unrealized (loss) gain on private company investments	$ (670,000)	$ 19,000
Other-than-temporary impairment loss	(117,000)	(75,000)
Private Company Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net change in unrealized (loss) gain on private company investments	0	100,000
Other-than-temporary impairment loss	$ (700,000)	$ 0