Income Taxes - Deferred Portion of Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Amortization of franchise rights	$ 495	$ 500	$ 514
Amortization of other intangibles	1,193	1,221	1,590
Accrued expenses, deducted for tax when paid	15,213	(6,889)	(17,664)
Capitalized costs for books, deducted for tax	(5,790)	5,901	5,315
Depreciation	(4,079)	(2,405)	(5,932)
Federal impact of unrecognized tax benefits	39	75	1,058
Foreign tax credit carryforwards	0	0	3,636
Tax effects of TCJA	34,633	0	0
Other, net	108	(271)	2,904
Deferred Portion Of Tax Expense Benefit, Total	$ 41,812	$ (1,868)	$ (8,579)