Cash and Marketable Securities - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Allowance for credit losses	$ 0		$ 0
Other-than-temporary impairment					$ 0
Unrealized gain on marketable securities	0
Tax benefit (provision)	$ (79,000)	$ 313,000	56,000	$ 313,000
Tax charge in other comprehensive income		$ 300,000	$ 100,000	$ 300,000
Effective maturity (less than)	2 years		2 years