Financial Commitments (Long-term Debt) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 20, 2010	Jun. 05, 2014	Aug. 03, 2011
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	$ 865,359,000	$ 733,884,000
Less - current maturities	(81,292,000)	(114,658,000)
Long-term debt, net	784,067,000	619,226,000
Loans repaid during the period	1,026,349,000	676,795,000	626,122,000
Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	300,000,000	300,000,000
Unamortized debt discount	(1,223,000)	(1,493,000)		(2,200,000)
Total long term-debt, net of unamortized debt discount	298,777,000	298,507,000
Maturity date	Nov. 01, 2018	Nov. 01, 2018
Interest rate (as a percent)	7.625%	7.625%
Imputed interest rate (as a percent)	7.75%	7.75%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	130,000,000	135,000,000
Face amount	300,000,000	300,000,000
Interest rate at lender's prime rate	3.25%	3.25%
Term Loan [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	242,500,000	115,000,000
Face amount	250,000,000	200,000,000			250,000,000	200,000,000
Term of debt	5 years	5 years
Equipment Financing [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	102,009,000	78,055,000
Term of debt	5 years	5 years
Interest rate, minimum (as a percent)	2.12%	2.12%
Interest rate, maximum (as a percent)	4.82%	4.82%
Balloon payments	8,300,000
Transportation Equipment Loan at Fixed Rate Of 6.44% [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount		29,582,000
Interest rate (as a percent)	6.44%	6.44%
Term of debt	5 years	5 years
Balloon payments	29,200,000
Transportation Equipment Loan at Fixed Rate Of 3.35% [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	27,954,000
Interest rate (as a percent)	3.35%	3.35%
Term of debt	10 years	10 years
Balloon payments	12,400,000
Lunda Seller Notes [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	21,750,000	21,750,000
Interest rate (as a percent)	5.00%	5.00%
Transportation Equipment Loan at Variable Rate [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	12,611,000	13,363,000
Term of debt	7 years
Balloon payments	12,000,000
Basis spread on variable rate (as a percent))	2.40%	2.40%
Land and Improvements Mortgages [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	9,144,000	9,404,000
Term of debt	10 years
Balloon payments	6,700,000
Basis spread on variable rate (as a percent))	3.00%	3.00%
Land and Office Building Mortgages [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	6,306,000	6,952,000
Term of debt	7 years
Basis spread on variable rate (as a percent))	2.00%	2.00%
Office Building Mortgages at Variable Rate [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	3,428,000	3,671,000
Interest rate at lender's prime rate	3.25%	3.25%
Term of debt	10 years
Balloon payments	2,600,000
Negative basis spread on variable rate	1.00%	1.00%
Land Mortgage [Member]
Debt Instrument [Line Items]
Balloon payments	3,000,000
Other Indebtedness [Member]
Debt Instrument [Line Items]
Total long term-debt, net of unamortized debt discount	10,880,000	22,600,000
Office Building Mortgages
Debt Instrument [Line Items]
Balloon payments	$ 2,600,000