Income Taxes Components of Net Deferred Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets [Abstract]
Net operating loss carryforwards	$ 27,211	$ 23,168
Accruals and reserves not deducted for tax purposes until paid	11,375	15,131
Stock-based compensation	8,634	10,089
Deferred revenue	4,588	8,289
Deferred compensation	3,496	3,891
Interest rate swaps	545	0
Alternative minimum tax credit carryforward	1,592	1,592
Pension and postretirement benefits	24,889	22,983
Other	1,992	2,072
Total deferred tax assets	232,229	304,269
Valuation allowance	(26,674)	(24,075)	$ (19,315)
Deferred tax liabilities [Abstract]
Interest rate swaps	0	(4,579)
Property and equipment basis difference	(700,488)	(1,016,349)
Intangible assets basis difference	(374,067)	(418,448)
Other	(851)	(368)
Net deferred tax liabilities	(869,851)	(1,159,550)
Track maintenance credit [Member]
Deferred tax assets [Abstract]
Track maintenance credit carryforward	$ 147,907	$ 217,054