CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
REVENUES	$ 1,861,489	$ 1,945,023	$ 1,809,807
COSTS AND EXPENSES:
Cost of revenues (exclusive of items shown separately below)	1,178,412	1,105,886	992,704
Selling, general and administrative expenses	185,165	175,749	151,286
Depreciation and amortization	213,128	214,899	179,905
Loss on disposition of assets, net	9,371	6,099	3,831
Operating profit	275,413	442,390	482,081
Interest expense	(1,822)	(1,976)	(3,453)
Interest income	419	30	18
Other income, net	2,260	2,175	169
Income before income taxes	276,270	442,619	478,815
Income tax provision	109,375	168,183	182,434
Net income	$ 166,895	$ 274,436	$ 296,381
EARNINGS PER SHARE
Basic (in dollars per share)	$ 0.77	$ 1.28	$ 1.36
Diluted (in dollars per share)	$ 0.77	$ 1.27	$ 1.35
Dividends paid per share (in dollars per share)	$ 0.40	$ 0.52	$ 0.21