Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	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
Fair Value Disclosures [Abstract]
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	$ 457	$ 791	$ 1,416	$ (508)	$ 97	$ (1,138)	$ 2,664	$ (1,549)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from available for sale municipal bonds							17,628	8,706
Unrealized gains related to equity securities (less than $0.1 million for the three months ended Sep 30, 2019)	100			1,600			5,000	2,900
Municipal bonds — available-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from available for sale municipal bonds	10,500			2,900			17,600	8,700
Realized gain (less than $0.1 million for the three months ended Sep 30, 2019)	$ 100						$ 100
Realized loss (less than $0.1 million for the three months ended September 30, 2018)				$ (100)				$ (200)