Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Taxes at statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	4.40%	3.90%	3.90%
Foreign tax rate differential	(0.30%)	(0.10%)	(0.30%)
Tax legislation	(22.60%)
Other permanent differences	0.70%	0.80%	1.90%
Prior year tax adjustments	(0.30%)	(1.00%)	(1.90%)
Unrecognized tax benefits	0.10%	1.00%
Valuation allowance	0.70%	(0.30%)
Equity-based compensation	(2.10%)	(1.00%)
Tax credits	(0.60%)	(0.80%)	(0.50%)
Taxes at effective rate	15.00%	37.50%	38.10%