Debt (Schedule of Debt Footnotes) (Details) | Jan. 05, 2018USD ($) | Dec. 20, 2017USD ($) | Feb. 03, 2017USD ($) | Nov. 26, 2014USD ($) | Mar. 31, 2018USD ($) | Mar. 31, 2017USD ($) | Mar. 31, 2018CAD ($) | Mar. 31, 2018EUR (€) | Mar. 31, 2018USD ($) | Dec. 31, 2017USD ($) | Mar. 16, 2017USD ($) |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt | | | | | | | | | $ 684,335,000 | $ 958,921,000 | |
Loss on settlement of debt | | | | | $ 21,515,000 | $ 10,696,000 | | | | | |
2019 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, repurchase amount | | | $ 227,000,000 | | | | | | | | |
Loss on settlement of debt | | | $ (10,696,000) | | | | | | | | |
2022 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | | | Dec. 1, 2022 | | | | | | | |
Debt, face amount | | | | $ 400,000,000 | | | | | 100,000,000 | | |
Debt, interest rate | | | | 7.75% | | | | | | | |
Debt | | | | | | | | | 98,710,000 | 394,565,000 | |
Debt, repurchase amount | $ 300,000,000 | | | | | | | | | | |
Loss on settlement of debt | $ (21,515,000) | | | | | | | | | | |
2024 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | | Feb. 1, 2024 | | | | | | | | |
Debt, face amount | | | $ 225,000,000 | | | | | | | | $ 25,000,000 |
Debt, interest rate | | | 6.50% | | | | | | | | |
Debt, issued price percentage of principal amount | | | | | | | | | | | 100.00% |
Debt | | | | | | | | | | | $ 244,711,000 |
2026 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | Jan. 15, 2026 | | | | | | | | | |
Debt, face amount | | $ 300,000,000 | | | | | | | 300,000,000 | | |
Debt, interest rate | | 5.50% | | | | | | | | | |
Debt, issued price percentage of principal amount | | 100.00% | | | | | | | | | |
Debt | | $ 293,795,000 | | | | | | | 294,011,000 | 293,773,000 | |
Senior Notes, redemption notice minimum days | | | | | 10 days | | | | | | |
Senior Notes, redemption notice maximum days | | | | | 60 days | | | | | | |
Senior Notes 2019 and 2022 [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, offering date | | | | | Nov. 26, 2014 | | | | | | |
Senior Notes 2022 and 2024 [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Senior Notes, redemption notice minimum days | | | | | 30 days | | | | | | |
Senior Notes, redemption notice maximum days | | | | | 60 days | | | | | | |
Stendal Credit Facility - EUR 75.0 Million [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | | | | Oct. 1, 2019 | | | | | | |
Debt | | | | | | | | | 0 | 0 | |
Debt, description of variable basis spread | | | | | Euribor | | | | | | |
Debt, variable basis spread | | | | | 3.50% | | | | | | |
Line of credit, maximum borrowing capacity | € | | | | | | | | € 75,000,000 | | | |
Line of credit, remaining borrowing capacity | | | | | | | | 74,869,000 | 92,246,000 | | |
Debt, amount of debt supporting bank guarantees | | | | | | | | 100,000 | 161,000 | | |
Celgar Credit Facility - C$40.0 Million [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | | | | May 1, 2019 | | | | | | |
Debt | | | | | | | | | 0 | 0 | |
Line of credit, maximum borrowing capacity | | | | | | | $ 40,000,000 | | | | |
Line of credit, letters of credit outstanding, amount | | | | | | | 1,700,000 | | 1,318,000 | | |
Line of credit, remaining borrowing capacity | | | | | | | $ 38,300,000 | | 29,705,000 | | |
Celgar Credit Facility - C$40.0 Million [Member] | Canadian Dollar Borrowings Rate Option 1 [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, description of variable basis spread | | | | | bankers acceptance | | | | | | |
Debt, variable basis spread | | | | | 1.50% | | | | | | |
Celgar Credit Facility - C$40.0 Million [Member] | Canadian Dollar Borrowings Rate Option 2 [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, description of variable basis spread | | | | | Canadian prime | | | | | | |
Celgar Credit Facility - C$40.0 Million [Member] | US Dollar Borrowings Rate Option 1 [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, description of variable basis spread | | | | | LIBOR | | | | | | |
Debt, variable basis spread | | | | | 1.50% | | | | | | |
Celgar Credit Facility - C$40.0 Million [Member] | US Dollar Borrowings Rate Option 2 [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, description of variable basis spread | | | | | U.S. base | | | | | | |
Rosenthal Credit Facility - EUR 5.0 Million [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | | | | Dec. 1, 2018 | | | | | | |
Debt | | | | | | | | | 0 | 0 | |
Debt, description of variable basis spread | | | | | three-month Euribor | | | | | | |
Debt, variable basis spread | | | | | 2.50% | | | | | | |
Line of credit, maximum borrowing capacity | € | | | | | | | | 5,000,000 | | | |
Line of credit, remaining borrowing capacity | | | | | | | | 2,400,000 | 3,016,000 | | |
Debt, amount of debt supporting bank guarantees | | | | | | | | € 2,600,000 | $ 3,144,000 | | |
Rosenthal Credit Facility - EUR 70.0 Million [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | | | | Apr. 1, 2022 | | | | | | |
Debt, interest rate | | | | | | | 2.95% | 2.95% | 2.95% | | |
Debt | | | | | | | | € 23,000,000 | $ 28,338,000 | 25,185,000 | |
Debt, description of variable basis spread | | | | | Euribor | | | | | | |
Debt, variable basis spread | | | | | 2.95% | | | | | | |
Line of credit, maximum borrowing capacity | € | | | | | | | | 70,000,000 | | | |
Line of credit, remaining borrowing capacity | | | | | | | | 35,400,000 | 43,578,000 | | |
Debt, amount of debt supporting bank guarantees | | | | | | | | € 11,600,000 | $ 14,331,000 | | |
Wood Procurement - EUR 25.0 Million [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, maturity date | | | | | Feb. 1, 2020 | | | | | | |
Debt, interest rate | | | | | | | 3.30% | 3.30% | 3.30% | | |
Debt | | | | | | | | € 14,400,000 | $ 17,689,000 | $ 0 | |
Debt, description of variable basis spread | | | | | Euribor | | | | | | |
Debt, variable basis spread | | | | | 3.30% | | | | | | |
Line of credit, maximum borrowing capacity | € | | | | | | | | 25,000,000 | | | |
Line of credit, remaining borrowing capacity | | | | | | | | 9,700,000 | 11,980,000 | | |
Debt, amount of debt supporting bank guarantees | | | | | | | | 900,000 | $ 1,134,000 | | |
Twelve month period beginning December 1, 2017 [Member] | 2022 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 105.813% | | | | | | |
Twelve month period beginning December 1, 2018 [Member] | 2022 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 103.875% | | | | | | |
Twelve month period beginning December 1, 2019 [Member] | 2022 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 101.938% | | | | | | |
Twelve month period beginning December 1, 2020 and at any time thereafter [Member] | 2022 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 100.00% | | | | | | |
Twelve month period beginning February 1, 2020 [Member] | 2024 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 103.25% | | | | | | |
Twelve month period beginning February 1, 2021 [Member] | 2024 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 101.625% | | | | | | |
Twelve month period beginning February 1, 2022 [Member] | 2024 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 100.00% | | | | | | |
Twelve month period beginning January 15, 2021 [Member] | 2026 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 102.75% | | | | | | |
Twelve month period beginning January 15, 2022 [Member] | 2026 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 101.375% | | | | | | |
Twelve month period beginning January 15, 2023 [Member] | 2026 Senior Notes [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Debt, redemption price, percentage | | | | | 100.00% | | | | | | |
Mercer Timber [Member] | Rosenthal Credit Facility - EUR 70.0 Million [Member] | | | | | | | | | | | |
Debt Instrument [Line Items] | | | | | | | | | | | |
Line of credit, maximum borrowing capacity | € | | | | | | | | € 45,000,000 | | | |