Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for a period longer than twelve months	$ 0
Allowance for credit losses	0
Impairment charges	0	$ 0
Marketable securities, due within one year	26,842,000		$ 34,874,000
Proceeds from maturities of available-for-sale securities	9,905,000	12,910,000
Proceeds from sale of marketable securities	0	$ 0
Variable rate demand notes
Debt Securities, Available-for-sale [Line Items]
Marketable securities, due within one year	$ 5,600,000
Variable rate demand notes | Minimum
Debt Securities, Available-for-sale [Line Items]
Contractual maturities (in years)	17 years
Settlement basis period (in days)	1 day
Effective maturity period (in days)	1 day
Variable rate demand notes | Maximum
Debt Securities, Available-for-sale [Line Items]
Contractual maturities (in years)	26 years
Settlement basis period (in days)	7 days
Effective maturity period (in days)	7 days