Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Effective tax rate	11.50%	11.10%
Economic interest held in company by class of stock (in hundredths)	74.10%	73.90%
Unrecognized tax benefits	$ 6,900,000		$ 6,500,000
Interest related to unrecognized tax benefits	1,000,000		800,000
Penalty accruals	0		0
Deferred tax assets	35,631,000		37,232,000
Valuation allowance on deferred tax assets	$ 0		$ 0