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Accumulated Other Comprehensive Loss (AOCL) - Changes in components of Accumulated other comprehensive loss (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |
Beginning Balance | $ (113,893) |  |  |  | $ (112,650) |  |  |  | $ (117,682) | $ (112,650) | $ (117,682) | $ (91,832)
Other comprehensive income (loss) before reclassifications |  |  |  |  |  |  |  |  |  | (9,521) | 7,311 | (43,345)
Net amount reclassified to net loss |  |  |  |  |  |  |  |  |  | 8,278 | (2,279) | 4,844
Elimination of equity in investee resulting from acquisition |  |  |  |  |  |  |  |  |  |  |  | 12,651
Ending Balance | (113,181) | $ (113,893) |  |  |  | $ (112,650) |  |  |  | (113,893) | (112,650) | (117,682)
Cost of goods sold | 348,935 |  |  |  | 321,906 |  |  |  |  | 1,330,136 | 1,908,544 | 1,729,243
Helguvik impairment |  |  |  |  |  |  |  |  |  | 152,220 | 0 | 0
Selling, general and administrative expenses | 10,702 |  |  |  | 9,625 |  |  |  |  | 40,264 | 42,115 | 49,195
Other operating expense, net | (973) |  |  |  | (881) |  |  |  |  | (3,857) | (7,436) | (12,481)
Income tax benefit (expense) | 308 |  |  |  | 2,070 |  |  |  |  | (2,824) | (9,276) | (18,308)
Net income (loss) | (15,139) | (168,464) | $ (58,273) | $ (9,515) | (16,163) | (43,080) | $ (56,112) | $ (33,897) | 73,779 | (252,415) | (59,310) | 126,474
Defined benefit plan liabilities [Member] |  |  |  |  |  |  |  |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |
Beginning Balance | (116,181) |  |  |  | (110,667) |  |  |  | (115,852) | (110,667) | (115,852) | (77,921)
Other comprehensive income (loss) before reclassifications |  |  |  |  |  |  |  |  |  | (9,521) | 7,311 | (42,926)
Net amount reclassified to net loss | 750 |  |  |  | 861 |  |  |  |  | 4,007 | (2,126) | 4,995
Elimination of equity in investee resulting from acquisition |  |  |  |  |  |  |  |  |  |  |  | 0
Ending Balance |  | (116,181) |  |  |  | (110,667) |  |  |  | (116,181) | (110,667) | (115,852)
Equity in investee other comprehensive income [Member] |  |  |  |  |  |  |  |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |
Beginning Balance | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 0 | (12,232)
Other comprehensive income (loss) before reclassifications |  |  |  |  |  |  |  |  |  | 0 | 0 | (419)
Net amount reclassified to net loss |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Elimination of equity in investee resulting from acquisition |  |  |  |  |  |  |  |  |  |  |  | 12,651
Ending Balance |  | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 0
Gain (loss) on financial instruments [Member] |  |  |  |  |  |  |  |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |
Beginning Balance | 2,288 |  |  |  | (1,983) |  |  |  | $ (1,830) | (1,983) | (1,830) | (1,679)
Other comprehensive income (loss) before reclassifications |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Net amount reclassified to net loss | (38) |  |  |  | (38) |  |  |  |  | 4,271 | (153) | (151)
Elimination of equity in investee resulting from acquisition |  |  |  |  |  |  |  |  |  |  |  | 0
Ending Balance |  | $ 2,288 |  |  |  | $ (1,983) |  |  |  | 2,288 | (1,983) | (1,830)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined benefit plan liabilities [Member] |  |  |  |  |  |  |  |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |
Cost of goods sold | 1,307 |  |  |  | 777 |  |  |  |  | 3,464 | (1,696) | 6,237
Selling, general and administrative expenses | 132 |  |  |  | 125 |  |  |  |  | 465 | 235 | 569
Other operating expense, net | 394 |  |  |  | 350 |  |  |  |  | 1,585 | 904 | 0
Income tax benefit (expense) | (1,083) |  |  |  | (391) |  |  |  |  | (1,507) | (1,569) | (1,811)
Net income (loss) | 750 |  |  |  | 861 |  |  |  |  | 4,007 | (2,126) | 4,995
Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity in investee other comprehensive income [Member] |  |  |  |  |  |  |  |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |
Cost of goods sold |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Income tax benefit (expense) |  |  |  |  |  |  |  |  |  | 0 | 0 | (419)
Net income (loss) |  |  |  |  |  |  |  |  |  | 0 | 0 | (419)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Gain (loss) on financial instruments [Member] |  |  |  |  |  |  |  |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |
Cost of goods sold | (46) |  |  |  | (46) |  |  |  |  | (185) | (186) | (185)
Helguvik impairment |  |  |  |  |  |  |  |  |  | 4,480 | 0 | 0
Income tax benefit (expense) | 8 |  |  |  | 8 |  |  |  |  | (24) | 33 | 34
Net income (loss) | $ (38) |  |  |  | $ (38) |  |  |  |  | $ 4,271 | $ (153) | $ (151)

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