Supplemental Guarantor Financial Information Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings (loss)	$ 863	$ 901	$ 16,415	$ 40,211
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	25,856	22,747	79,468	65,921
Equity-based compensation expense			2,523	9,826
Deferred tax expense (benefit)			14,602	12,329
Employee benefit plans			2,999	500
Gain (Loss) on Disposition of Assets			3,755	30
Increase (Decrease) in Other Operating Assets and Liabilities, Net			874	484
Changes in working capital, net			43,846	4,045
Change in taxes receivable, net			(4,869)	7,217
Other Operating Activities, Cash Flow Statement			(1,439)	(680)
Net cash provided by operating activities			152,176	138,883
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment			(136,650)	(105,514)
Payments for (Proceeds from) Other Investing Activities			753	250
Net cash used for investing activities			(135,897)	(105,264)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments for Repurchase of Common Stock			(4,875)	(51,528)
Investment (to) from Parent			0	0
Proceeds from Lines of Credit			185,000	944,844
Repayments of Lines of Credit			(210,000)	(931,832)
Payment of tax withholdings on equity-based payment arrangements			(790)
Proceeds from (Payments for) Other Financing Activities			(927)	(382)
Net cash (used for) provided by financing activities			(30,802)	(38,898)
Decrease in cash and cash equivalents			(14,523)	(5,279)
Cash at beginning of period			23,001	5,610
Cash at end of period	8,478	331	8,478	331
Issuer
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings (loss)	1,445	901	18,855	40,211
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization			56,642	50,214
Equity-based compensation expense			2,523	9,826
Deferred tax expense (benefit)			19,531	11,641
Employee benefit plans			2,999	500
Gain (Loss) on Disposition of Assets			481	30
Increase (Decrease) in Other Operating Assets and Liabilities, Net			874	471
Changes in working capital, net			32,501	1,961
Change in taxes receivable, net			600	6,178
Other Operating Activities, Cash Flow Statement			(413)	(1,205)
Net cash provided by operating activities			128,595	118,827
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment			(132,725)	(99,912)
Payments for (Proceeds from) Other Investing Activities			283	250
Net cash used for investing activities			(132,442)	(99,662)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments for Repurchase of Common Stock			(4,875)	(51,528)
Investment (to) from Parent			23,541	14,454
Proceeds from Lines of Credit			185,000	944,844
Repayments of Lines of Credit			(210,000)	(931,832)
Proceeds from (Payments for) Other Financing Activities			(927)	(382)
Net cash (used for) provided by financing activities			(7,261)	(24,444)
Decrease in cash and cash equivalents			(11,108)	(5,279)
Cash at beginning of period			19,586	5,610
Cash at end of period	8,478	331	8,478	331
Guarantor Subsidiaries
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings (loss)	(641)	2,304	(398)	4,607
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization			22,826	15,707
Equity-based compensation expense			0	0
Deferred tax expense (benefit)			(4,929)	1,826
Employee benefit plans			0	0
Gain (Loss) on Disposition of Assets			3,274	0
Increase (Decrease) in Other Operating Assets and Liabilities, Net			0	13
Changes in working capital, net			3,896	4,531
Change in taxes receivable, net			0	(1,408)
Other Operating Activities, Cash Flow Statement			(1,026)	(613)
Net cash provided by operating activities			23,643	24,663
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment			(3,925)	(5,602)
Payments for (Proceeds from) Other Investing Activities			470	0
Net cash used for investing activities			(3,455)	(5,602)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments for Repurchase of Common Stock			0	0
Investment (to) from Parent			(23,603)	(19,061)
Proceeds from Lines of Credit			0	0
Repayments of Lines of Credit			0	0
Proceeds from (Payments for) Other Financing Activities			0	0
Net cash (used for) provided by financing activities			(23,603)	(19,061)
Decrease in cash and cash equivalents			(3,415)	0
Cash at beginning of period			3,415	0
Cash at end of period	0	0	0	0
Eliminations
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings (loss)	59	(2,304)	(2,042)	(4,607)
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization			0	0
Equity-based compensation expense			0	0
Deferred tax expense (benefit)			0	(1,138)
Employee benefit plans			0	0
Gain (Loss) on Disposition of Assets			0	0
Increase (Decrease) in Other Operating Assets and Liabilities, Net			0	0
Changes in working capital, net			7,449	(2,447)
Change in taxes receivable, net			(5,469)	2,447
Other Operating Activities, Cash Flow Statement			0	1,138
Net cash provided by operating activities			(62)	(4,607)
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment			0	0
Payments for (Proceeds from) Other Investing Activities			0	0
Net cash used for investing activities			0	0
CASH FLOWS FROM FINANCING ACTIVITIES
Payments for Repurchase of Common Stock			0	0
Investment (to) from Parent			62	4,607
Proceeds from Lines of Credit			0	0
Repayments of Lines of Credit			0	0
Proceeds from (Payments for) Other Financing Activities			0	0
Net cash (used for) provided by financing activities			62	4,607
Decrease in cash and cash equivalents			0	0
Cash at beginning of period			0	0
Cash at end of period	$ 0	$ 0	$ 0	$ 0