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Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Components of Net Periodic Pension Cost |  |  |
Service cost—benefits earned during the period | $ 0 | $ 463 | $ 2,601
Interest cost on projected benefit obligation | 4,100 | 4,296 | 4,425
Expected return on plan assets | (6,313) | (5,780) | (7,180)
Amortization of prior service credit | 0 | (11) | (138)
Recognized net actuarial loss | 1,866 | 2,345 | 2,028
Curtailment gain | 0 | (1,017) | 0
Net Periodic Pension Expense | (347) | 296 | 1,736
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss) |  |  |
Net actuarial (gain) loss | 3,678 | (6,018) | 5,678
Recognized net actuarial loss | (1,866) | (2,345) | (2,028)
Recognized prior service credit | 0 | 1,029 | 138
Total (Before Tax Effects) | 1,812 | (7,334) | 3,788
Total Recognized in Net Benefit Cost and Other Comprehensive (Loss)/Income (Before Tax Effects) | $ 1,465 | $ (7,038) | $ 5,524

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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