CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenues	$ 470,999	$ 175,884	$ 1,167,928	$ 507,977
Cost of revenues (exclusive of items shown below)	294,820	146,615	765,078	434,868
Selling, general and administrative expenses	39,738	34,859	117,183	114,863
Depreciation and amortization	39,587	51,975	125,513	168,891
Gain on disposition of assets, net	(503)	(1,148)	(5,779)	(3,919)
Operating income (loss)	97,357	(56,417)	165,933	(206,726)
Interest expense	(105)	(115)	(322)	(566)
Interest income	488	169	1,028	296
Other income, net	564	86	2,786	274
Income (loss) before income taxes	98,304	(56,277)	169,425	(206,722)
Income tax provision (benefit)	40,970	(17,335)	64,617	(86,583)
Net income (loss)	$ 57,334	$ (38,942)	$ 104,808	$ (120,139)
Earnings (loss) per share
Basic (in dollars per share)	$ 0.26	$ (0.18)	$ 0.48	$ (0.56)
Diluted (in dollars per share)	0.26	$ (0.18)	0.48	$ (0.56)
Dividends per share (in dollars per share)	$ 0.06		$ 0.06