Income Taxes - Income tax rate reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	35.00%	35.00%
Non-deductibility of goodwill impairment	(0.00%)	(29.30%)	(0.00%)
Change in federal tax rate	0.00%	15.50%	0.00%
State and other taxes, net of federal tax benefit	3.60%	0.40%	2.70%
Change in unrecognized tax benefits	3.30%	(0.70%)	0.40%
Change in valuation allowance	0.40%	0.30%	0.00%
Domestic production activity deduction	(0.00%)	0.30%	(0.60%)
Changes in tax rates and state tax laws	(1.60%)	(0.30%)	(1.70%)
Change in accounting for excess tax deficiencies/benefits	0.10%	(0.50%)	(0.00%)
Other	0.60%	(0.70%)	0.20%
Effective tax rate	27.40%	20.00%	36.00%