Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Sales:
Product	$ 246,022	$ 116,039	$ 455,343	$ 237,666
Service	44,443	955	79,919	1,838
Total sales	290,465	116,994	535,262	239,504
Cost of sales (excluding depreciation, depletion and amortization):
Product	164,025	102,587	326,662	209,216
Service	33,386	120	58,224	242
Total cost of sales (excluding depreciation, depletion and amortization)	197,411	102,707	384,886	209,458
Operating expenses:
Selling, general and administrative	26,012	14,585	48,353	30,088
Depreciation, depletion and amortization	23,626	15,209	45,225	29,765
Total operating expenses	49,638	29,794	93,578	59,853
Operating income (loss)	43,416	(15,507)	56,798	(29,807)
Other income (expense):
Interest expense	(8,105)	(6,647)	(15,751)	(13,290)
Other income (expense), net, including interest income	1,258	608	(3,670)	2,398
Total other income (expenses)	(6,847)	(6,039)	(19,421)	(10,892)
Income (loss) before income taxes	36,569	(21,546)	37,377	(40,699)
Income tax benefit (expense)	(7,110)	9,774	(5,396)	17,924
Net income (loss)	$ 29,459	$ (11,772)	$ 31,981	$ (22,775)
Earnings (loss) per share:
Basic (in usd per share)	$ 0.36	$ (0.19)	$ 0.39	$ (0.38)
Diluted (in usd per share)	$ 0.36	$ (0.19)	$ 0.39	$ (0.38)
Weighted average shares outstanding:
Weighted average number of shares outstanding, basic	81,087	63,417	81,032	58,900
Weighted average number of shares outstanding, diluted	81,945	63,417	82,103	58,900
Common stock cash dividend declared, per share	$ 0.0625	$ 0.0625	$ 0.125	$ 0.125