CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenues	$ 436,334	$ 298,119
Cost of revenues (exclusive of items shown below)	295,605	216,242
Selling, general and administrative expenses	43,814	37,157
Depreciation and amortization	37,480	44,663
Gain on disposition of assets, net	(1,363)	(1,517)
Operating income	60,798	1,574
Interest expense	(105)	(103)
Interest income	402	129
Other income, net	5,395	212
Income before income taxes	66,490	1,812
Income tax provision (benefit)	14,360	(1,822)
Net income	$ 52,130	$ 3,634
Earnings per share
Basic (in dollars per share)	$ 0.24	$ 0.02
Diluted (in dollars per share)	0.24	$ 0.02
Dividends per share (in dollars per share)	$ 0.10