Supplemental Guarantor Financial Information - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings	$ (10,973)	$ (424)	$ 3,837	$ 34,444	$ 6,961	$ 2,600	$ (7,560)	$ 44,005
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	31,990			25,342			86,343	75,686
Equity-based compensation expense							2,959	2,845
Deferred tax expense							(6,023)	3,930
Employee benefit plans							1,006	102
Amortization of deferred issuance costs on debt							1,452	943
Loss on retirement of debt	2,725			0			2,725	0
Gain on divested assets							0	(25,510)
Other non-cash activity, net							724	84
Changes in working capital, net							(98,266)	7,402
Changes in taxes receivable							(420)	13,534
Other, net							825	(1,922)
Net cash provided by operating activities							(16,235)	121,099
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment							(125,794)	(174,034)
Net proceeds from divested assets							0	70,930
Other, net							14	807
Net cash used for investing activities							(125,780)	(102,297)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings on short-term debt							534,877	322,454
Repayments of borrowings on short-term debt							(598,715)	(277,454)
Borrowings on long-term debt							296,146	0
Repayments of borrowings on long-term debt							(101,671)	0
Payments for debt issuance costs							(1,844)	0
Investment (to) from Parent							0	0
Other, net							(1,430)	(853)
Net cash (used for) provided by financing activities							127,363	44,147
(Decrease) increase in cash, cash equivalents and restricted cash							(14,652)	62,949
Cash, cash equivalents and restricted cash at beginning of period			24,947			16,738	24,947	16,738
Cash, cash equivalents and restricted cash at end of period	10,295			79,687			10,295	79,687
Parent Company [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings	(6,440)			32,311			(346)	45,437
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization							74,186	59,632
Equity-based compensation expense							2,959	2,845
Deferred tax expense							(10,286)	10,662
Employee benefit plans							1,006	102
Amortization of deferred issuance costs on debt							1,452	943
Loss on retirement of debt	2,725						2,725
Gain on divested assets								0
Other non-cash activity, net							734	84
Changes in working capital, net							(111,631)	22,045
Changes in taxes receivable							9,918	8,053
Other, net							1,086	(1,800)
Net cash provided by operating activities							(28,197)	148,003
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment							(124,111)	(172,434)
Net proceeds from divested assets								70,930
Other, net							4	793
Net cash used for investing activities							(124,107)	(100,711)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings on short-term debt							534,877	322,454
Repayments of borrowings on short-term debt							(598,715)	(277,454)
Borrowings on long-term debt							296,146
Repayments of borrowings on long-term debt							(101,671)
Payments for debt issuance costs							(1,844)
Investment (to) from Parent							10,289	(28,490)
Other, net							(1,430)	(853)
Net cash (used for) provided by financing activities							137,652	15,657
(Decrease) increase in cash, cash equivalents and restricted cash							(14,652)	62,949
Cash, cash equivalents and restricted cash at beginning of period			24,947			16,738	24,947	16,738
Cash, cash equivalents and restricted cash at end of period	10,295			79,687			10,295	79,687
Guarantor Subsidiaries [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings	1,542			16,805			5,029	17,981
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization							12,157	16,054
Equity-based compensation expense							0	0
Deferred tax expense							4,263	(6,732)
Employee benefit plans							0	0
Amortization of deferred issuance costs on debt							0	0
Loss on retirement of debt	0						0
Gain on divested assets								(25,510)
Other non-cash activity, net							(10)	0
Changes in working capital, net							2,504	(7,383)
Changes in taxes receivable							17	26
Other, net							(261)	(122)
Net cash provided by operating activities							23,699	(5,686)
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment							(1,683)	(1,600)
Net proceeds from divested assets								0
Other, net							10	14
Net cash used for investing activities							(1,673)	(1,586)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings on short-term debt							0	0
Repayments of borrowings on short-term debt							0	0
Borrowings on long-term debt							0
Repayments of borrowings on long-term debt							0
Payments for debt issuance costs							0
Investment (to) from Parent							(22,026)	7,272
Other, net							0	0
Net cash (used for) provided by financing activities							(22,026)	7,272
(Decrease) increase in cash, cash equivalents and restricted cash							0	0
Cash, cash equivalents and restricted cash at beginning of period			0			0	0	0
Cash, cash equivalents and restricted cash at end of period				0				0
Eliminations
CASH FLOWS FROM OPERATING ACTIVITIES
Net earnings	(6,075)			(14,672)			(12,243)	(19,413)
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							0	0
Employee benefit plans							0	0
Amortization of deferred issuance costs on debt							0	0
Loss on retirement of debt	$ 0						0
Gain on divested assets								0
Other non-cash activity, net								0
Changes in working capital, net							10,861	(7,260)
Changes in taxes receivable							(10,355)	5,455
Other, net							0	0
Net cash provided by operating activities							(11,737)	(21,218)
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to plant and equipment							0	0
Net proceeds from divested assets								0
Other, net							0	0
Net cash used for investing activities							0	0
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings on short-term debt							0	0
Repayments of borrowings on short-term debt							0	0
Borrowings on long-term debt							0
Repayments of borrowings on long-term debt							0
Payments for debt issuance costs							0
Investment (to) from Parent							11,737	21,218
Other, net							0	0
Net cash (used for) provided by financing activities							11,737	21,218
(Decrease) increase in cash, cash equivalents and restricted cash							0	0
Cash, cash equivalents and restricted cash at beginning of period			$ 0			$ 0	$ 0	0
Cash, cash equivalents and restricted cash at end of period				$ 0				$ 0