Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Statement of Cash Flows [Abstract]
Restricted Cash	$ 556		$ 0		$ 556	$ 0
Net income (loss)	(15,260)	[1]	37,141	[1]	25,080	72,361
Operating Activities:
Depreciation and amortization	15,117		12,545		29,376	25,642
Equity (income) loss from equity method investments	(472)		(64)		(222)	5
Non-cash debt and financing costs					1,914	635
Stock-based compensation expense					6,871	8,477
(Gain) loss on write down and disposal of long-lived assets	59		312		1,019	823
Pension and other post-retirement benefits					2,663	2,549
Change in deferred income taxes					16,505	578
Change in operating assets					(46,220)	(19,956)
Change in operating liabilities					15,212	(58,049)
Other					(528)	(66)
Net Cash Provided by (Used in) Operating Activities					51,670	32,999
Investing activities:
Capital expenditures					(73,351)	(40,478)
Payments for (Proceeds from) Hedge, Investing Activities					4,536	0
Acquisitions, net of cash received					(1,294)	0
Payments to Acquire Interest in Joint Venture					(2,000)	(1,000)
Net Cash Provided by (Used in) Investing Activities					(71,676)	(40,702)
Financing activities:
Proceeds from Issuance of Secured Debt					21,540	510
Proceeds from Hedge, Financing Activities					6,476	0
Payments for (Proceeds from) Hedge, Financing Activities					(2,839)	0
Finance Lease, Principal Payments	(378)				(745)	0
Payments of long-term debt					(13,149)	(8,625)
Proceeds from exercise of stock options					118	471
Payments of Ordinary Dividends, Common Stock	(2,903)				(5,803)	0
Net Cash Provided by (Used in) Financing Activities					5,598	(7,644)
Proceeds from Equity Method Investment, Distribution					433	776
Net increase (decrease) in cash, cash equivalents and restricted cash					(14,408)	(15,347)
Effect of foreign currency fluctuations on cash, cash equivalents and restricted cash					(252)	(8,452)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	193,258		263,047		193,258	263,047
Cash, cash equivalents, and restricted cash, at end of fiscal period	$ 192,702		$ 263,047		$ 192,702	$ 263,047

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