Supplemental Guarantor Financial Information Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings (loss)	$ 8,037	$ 20,864	$ 15,552	$ 39,310
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	26,055	22,024	53,612	43,174
Equity-based compensation expense			403	7,716
Deferred tax expense (benefit)			7,891	8,674
Employee benefit plans			2,183	2,561
Increase (Decrease) in Other Operating Assets and Liabilities, Net			1,267	259
Changes in working capital, net			23,742	(13,394)
Change in taxes receivable, net			4,229	14,107
Other Operating Activities, Cash Flow Statement			(914)	(870)
Net cash provided by operating activities			103,599	96,415
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment			(85,709)	(57,394)
Payments for (Proceeds from) Other Investing Activities			417	250
Net cash used for investing activities			(85,292)	(57,144)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments for Repurchase of Common Stock			(4,875)	(35,168)
Investment (to) from Parent			0	0
Proceeds from Lines of Credit			117,000	477,169
Repayments of Lines of Credit			(144,000)	(477,169)
Payment of tax withholdings on equity-based payment arrangements			(790)
Proceeds from (Payments for) Other Financing Activities			(914)	(318)
Net cash (used for) provided by financing activities			(32,789)	(35,486)
Increase in cash			(14,482)	3,785
Cash at beginning of period			23,001	5,610
Cash at end of period	8,519	9,395	8,519	9,395
Issuer
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings (loss)	8,556	20,864	17,410	39,310
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization			37,335	32,905
Equity-based compensation expense			403	7,716
Deferred tax expense (benefit)			7,183	7,858
Employee benefit plans			2,183	2,561
Increase (Decrease) in Other Operating Assets and Liabilities, Net			922	250
Changes in working capital, net			(29,619)	(18,437)
Change in taxes receivable, net			9,710	14,000
Other Operating Activities, Cash Flow Statement			(373)	(854)
Net cash provided by operating activities			40,788	80,187
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment			(82,582)	(54,049)
Payments for (Proceeds from) Other Investing Activities			20	250
Net cash used for investing activities			(82,562)	(53,799)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments for Repurchase of Common Stock			(4,875)	(35,168)
Investment (to) from Parent			63,496	12,883
Proceeds from Lines of Credit			117,000	477,169
Repayments of Lines of Credit			(144,000)	(477,169)
Proceeds from (Payments for) Other Financing Activities			(914)	(318)
Net cash (used for) provided by financing activities			30,707	(22,603)
Increase in cash			(11,067)	3,785
Cash at beginning of period			19,586	5,610
Cash at end of period	8,519	9,395	8,519	9,395
Guarantor Subsidiaries
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings (loss)	(172)	1,239	243	2,303
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization			16,277	10,269
Equity-based compensation expense			0	0
Deferred tax expense (benefit)			708	1,954
Employee benefit plans			0	0
Increase (Decrease) in Other Operating Assets and Liabilities, Net			345	9
Changes in working capital, net			46,811	6,555
Change in taxes receivable, net			6	(1,405)
Other Operating Activities, Cash Flow Statement			(541)	(16)
Net cash provided by operating activities			63,849	19,669
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment			(3,127)	(3,345)
Payments for (Proceeds from) Other Investing Activities			397	0
Net cash used for investing activities			(2,730)	(3,345)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments for Repurchase of Common Stock			0	0
Investment (to) from Parent			(64,534)	(16,324)
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			(64,534)	(16,324)
Increase in cash			(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)	(347)	(1,239)	(2,101)	(2,303)
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
Increase (Decrease) in Other Operating Assets and Liabilities, Net			0	0
Changes in working capital, net			6,550	(1,512)
Change in taxes receivable, net			(5,487)	1,512
Other Operating Activities, Cash Flow Statement			0	0
Net cash provided by operating activities			(1,038)	(3,441)
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			1,038	3,441
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			1,038	3,441
Increase in cash			0	0
Cash at beginning of period			0	0
Cash at end of period	$ 0	$ 0	$ 0	$ 0