Income Taxes Components of Net Deferred Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets [Abstract]
Net operating loss carryforwards	$ 20,810	$ 16,008
Accruals and reserves not deducted for tax purposes until paid	14,896	11,027
Stock-based compensation	9,253	6,954
Deferred revenue	5,736	3,652
Deferred compensation	3,454	2,810
Nonshareholder contributions	2,150	1,871
Interest rate swaps	4,223	1,664
Alternative minimum tax credit	1,592	1,592
Postretirement benefits	15,411	425
Other	752	457
Total deferred tax assets	315,688	275,526
Valuation allowance	(19,315)	(14,793)
Deferred tax liabilities [Abstract]
Property and intangible basis difference	(1,270,901)	(1,088,572)
Other	(6,338)	(1,519)
Net deferred tax liabilities	(980,866)	(829,358)
Track maintenance credit [Member]
Deferred tax assets [Abstract]
Tax credit carryforward	237,411	227,102
Foreign tax credit [Member]
Deferred tax assets [Abstract]
Tax credit carryforward	$ 0	$ 1,964