Income Taxes Provision for Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current Federal Tax Provision	$ 20,877,000	$ 12,003,000	$ 15,647,000
Current State Tax Provision	11,284,000	8,181,000	7,134,000
Deferred Federal Income Tax Provision	43,820,000	41,975,000	49,799,000
Deferred State Income Tax Provision	2,263,000	5,383,000	8,727,000
Current Foreign Tax Provision	3,289,000	11,031,000	17,591,000
Deferred Foreign Income Tax (Benefit)/Provision	(7,138,000)	(2,679,000)	8,209,000
Foreign Income Tax (Benefit)/Provision	(3,849,000)	8,352,000	25,800,000
Provision for income taxes	$ 74,395,000	75,894,000	107,107,000
Tax Adjustments, Settlements, and Unusual Provisions			3,900,000
Tax credits percentage of qualified maintenance expenditures to reduce federal income tax	50.00%
Tax credit limitation per mile on maintenance expenditures to reduce federal income tax	$ 3,500
Foreign Tax Authority [Member]
Tax benefit from tax rate adjustment	4,300,000	9,700,000
United States [Member]
Deferred United States Tax Provision	$ 78,244,000	$ 67,542,000	$ 81,307,000