Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands		Jun. 30, 2019	Mar. 31, 2019
Statement of Financial Position [Abstract]
Accrued expenses	[1]	$ 79,173	$ 93,761
Property, Plant and Equipment, Net [Abstract]
Property and equipment, accumulated depreciation		$ 889,142	$ 866,614
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, par value (in dollars per share)		$ 0.01	$ 0.01
Preferred stock, authorized shares		10,000,000	10,000,000
Preferred stock, issued shares		0	0
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, par value (in dollars per share)		$ 0.01003130893	$ 0.01020462209
Common stock, authorized shares		175,000,000	175,000,000
Common stock, issued shares		57,818,975	56,641,000

[1]   June 30, 2019   March 31, 2019 ASSETS  
   
Current assets:  
   
Cash and cash equivalents $ 217,307
  $ 207,918
Accounts receivable, net 154,522
  154,059
Inventories, net 256,140
  241,129
Prepaid expenses and other current assets 48,187
  38,947
Total current assets 676,156
  642,053
Property, plant and equipment, net of accumulated depreciation of $889,142 and $880,451 as of June 30, 2019 and March 31, 2019, respectively 518,310
  495,280
Goodwill 40,294
  40,294
Intangible assets, net 53,448
  53,749
Equity method investments 14,238
  12,925
Deferred income taxes  44,544
  57,024
Other assets 44,216
  16,770
Total assets $ 1,391,206
  $ 1,318,095
        LIABILITIES AND STOCKHOLDERS’ EQUITY  
   
Current liabilities:  
   
Current portion of long-term debt $ 29,225
  $ 28,430
Accounts payable 161,853
  153,287
Accrued expenses 79,173
  93,761
Income taxes payable 808
  2,995
Total current liabilities  271,059
  278,473
Long-term debt 282,871
  266,041
Other non-current obligations 149,267
  125,360
Deferred income taxes  11,214
  8,806
Total liabilities 714,411
  678,680
Stockholders’ equity:  
   
Preferred stock, par value $0.01, authorized 10,000 shares, none issued —
  —
Common stock, par value $0.01, authorized 175,000 shares, issued 58,018 and 57,822 shares at June 30, 2019 and March 31, 2019, respectively 580
  578
Additional paid-in capital 466,704
  465,366
Retained earnings 241,635
  204,195
Accumulated other comprehensive income (loss) (32,124 )   (30,724 ) Total stockholders’ equity 676,795
  639,415
Total liabilities and stockholders’ equity $ 1,391,206
  $ 1,318,095