Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Sales:
Total sales	$ 427,433	$ 290,465	$ 796,746	$ 535,262
Cost of sales (excluding depreciation, depletion and amortization):
Product	236,236	162,238	443,475	324,134
Service	56,609	34,726	110,280	60,018
Total cost of sales (excluding depreciation, depletion and amortization)	292,845	196,964	553,755	384,152
Operating expenses:
Selling, general and administrative	42,232	25,839	76,823	47,978
Depreciation, depletion and amortization	36,563	23,626	65,155	45,225
Asset impairment	16,184	0	16,184	0
Total operating expenses	94,979	49,465	158,162	93,203
Operating income	39,609	44,036	84,829	57,907
Other (expense) income:
Interest expense	(20,214)	(8,105)	(27,284)	(15,751)
Other income (expense), net, including interest income	1,081	638	1,746	(4,779)
Total other expense	(19,133)	(7,467)	(25,538)	(20,530)
Income before income taxes	20,476	36,569	59,291	37,377
Income tax expense	(2,832)	(7,110)	(10,353)	(5,396)
Net income	$ 17,644	$ 29,459	$ 48,938	$ 31,981
Earnings per share:
Basic (in dollars per share)	$ 0.23	$ 0.36	$ 0.62	$ 0.39
Diluted (in dollars per share)	$ 0.22	$ 0.36	$ 0.62	$ 0.39
Weighted average shares outstanding:
Basic (shares)	77,784	81,087	78,636	81,032
Diluted (shares)	78,480	81,945	79,328	82,103
Dividends declared per share (in dollars per share)	$ 0.0625	$ 0.0625	$ 0.13	$ 0.13
Product
Sales:
Total sales	$ 345,957	$ 235,891	$ 640,745	$ 439,143
Service
Sales:
Total sales	$ 81,476	$ 54,574	$ 156,001	$ 96,119