Income Taxes (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective tax rate	11.10%	11.90%
Economic interest held in company by class of stock (in hundredths)	73.90%	74.70%
Unrecognized tax benefits	$ 5,200,000		$ 4,700,000
Interest related to unrecognized tax benefits	600,000		500,000
Penalty accruals	0		0
Deferred tax assets	38,294,000		39,639,000
Valuation allowance on deferred tax assets	$ 0		$ 0