| **Restructuring (Schedule of Restructuring and Exit Costs In Consolidated Statements Of Operations) (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended | 12 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|-----------------|
||
| **Restructuring Cost and Reserve [Line Items]**                                                                                                                 |           |            |   |   |
| Restructuring and exit costs                                                                                                                                    | $ 634          | $ 2,521         | $ 2,184 | $ 7,290 |
| Income tax benefit                                                                                                                                              |           | (655)           | (830) | (2,836) |
| Impact on net loss from continuing operations                                                                                                                   | 393            | 1,866           | 1,354 | 4,454 |
| Custom Sheet and Rollstock                                                                                                                                      |           |            |   |   |
| **Restructuring Cost and Reserve [Line Items]**                                                                                                                 |           |            |   |   |
| Restructuring and exit costs                                                                                                                                    |           | 1,054           | 609 | 2,585 |
| Packaging Technologies                                                                                                                                          |           |            |   |   |
| **Restructuring Cost and Reserve [Line Items]**                                                                                                                 |           |            |   |   |
| Restructuring and exit costs                                                                                                                                    |           | 0               | 247 | (662) |
| Color and Specialty Compounds                                                                                                                                   |           |            |   |   |
| **Restructuring Cost and Reserve [Line Items]**                                                                                                                 |           |            |   |   |
| Restructuring and exit costs                                                                                                                                    |           | 1,467           | 1,322 | 5,276 |
| Corporate                                                                                                                                                       |           |            |   |   |
| **Restructuring Cost and Reserve [Line Items]**                                                                                                                 |           |            |   |   |
| Restructuring and exit costs                                                                                                                                    |           | $ 0             | $ 6 | $ 91 |

| X                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Restructuring Charges Income Tax Expense Benefit
+ References
No definition available.
+ Details**Name:**seh_RestructuringChargesIncomeTaxExpenseBenefit**Namespace Prefix:**seh_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Restructuring Charges Net Of Income Tax
+ References
No definition available.
+ Details**Name:**seh_RestructuringChargesNetOfIncomeTax**Namespace Prefix:**seh_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount charged against earnings in the period for incurred and estimated costs associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, excluding asset retirement obligations.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.P.3) -URI http://asc.fasb.org/extlink&oid=6394695&loc=d3e140864-122747Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=6394695&loc=d3e140904-122747
+ Details**Name:**us-gaap_RestructuringCharges**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RestructuringCostAndReserveLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |