Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	$ 174,876	$ 152,748
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to Property, Plant, and Equipment	(93,444)	(44,851)
Proceeds from Sale of Property, Plant, and Equipment	2,281
Acquisition Spending		(36,761)
Net Cash Used in Investing Activities	(91,163)	(81,612)
CASH FLOWS FROM FINANCING ACTIVITIES
Increase (Repayment) of Credit Facility	10,000	(30,000)
Dividends Paid to Stockholders	(9,582)	(9,709)
Purchase and Retirement of Common Stock	(122,404)	(24,903)
Proceeds from Stock Option Exercises	1,992	20,426
Shares Redeemed to Settle Employee Taxes on Stock Compensation	(1,785)	(2,455)
Net Cash Used in Financing Activities	(121,779)	(46,641)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	(38,066)	24,495
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	48,068	6,561
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	10,002	31,056
Parent [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	(69,161)	21,447
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to Property, Plant, and Equipment	(1,133)
Net Cash Used in Investing Activities	(1,133)
CASH FLOWS FROM FINANCING ACTIVITIES
Increase (Repayment) of Credit Facility	10,000	(30,000)
Dividends Paid to Stockholders	(9,582)	(9,709)
Purchase and Retirement of Common Stock	(122,404)	(24,903)
Proceeds from Stock Option Exercises	1,992	20,426
Shares Redeemed to Settle Employee Taxes on Stock Compensation	(1,785)	(2,455)
Intra-entity Activity, net	155,120	49,072
Net Cash Used in Financing Activities	33,341	2,431
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	(36,953)	23,878
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	44,537	5,184
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	7,584	29,062
Guarantor Subsidiaries [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	244,037	131,301
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to Property, Plant, and Equipment	(92,311)	(44,851)
Proceeds from Sale of Property, Plant, and Equipment	2,281
Acquisition Spending		(36,761)
Net Cash Used in Investing Activities	(90,030)	(81,612)
CASH FLOWS FROM FINANCING ACTIVITIES
Intra-entity Activity, net	(155,120)	(49,072)
Net Cash Used in Financing Activities	(155,120)	(49,072)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	(1,113)	617
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	3,531	1,377
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	$ 2,418	$ 1,994