Employee Benefits (Details 2) (USD $)	12 Months Ended
Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012
Deferred compensation plan
Number of investments, which are taken as reference to measure the interest that may be acquired	3
Employer contribution as percentage of the employees' reduced compensation	3.00%
Number of deferred compensation plans	2seb_NumberOfDeferredCompensationPlans
Deferred compensation plan expense	$ 3,142,000	$ 5,942,000	$ 4,148,000
Deferred compensation plan liability included in other liabilities	42,759,000	41,144,000
Deferred compensation plan assets included in other current assets	47,635,000us-gaap_DeferredCompensationPlanAssets	45,350,000us-gaap_DeferredCompensationPlanAssets
Investment income related to the mark-to-market of investments treated as trading securities	3,086,000	5,863,000	4,076,000
Defined contribution plan covering domestic, salaried and clerical employees
Defined contribution plans
Employer contribution (as a percent of employee contributions)	50.00%	50.00%	50.00%
Employer contribution limit per calendar year (as a percent of compensation)	6.00%	6.00%	6.00%
Vesting percentage after one year of service	20.00%
Additional vesting percentage with each additional complete year of service	20.00%
Contribution expense	$ 2,245,000	$ 2,142,000	$ 2,063,000

The compensation expense recognized during the period relating to the deferred compensation arrangement.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the employer's contribution as a percentage of employees' reduced compensation under the deferred compensation plan which allows certain employees to reduce their compensation in exchange for values in investments.

+ References

No definition available.

+ Details

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- Definition

Represents the number of investments, which are taken as reference to measure the interest that may be acquired by employees in exchange for reduction in their compensation.

+ References

No definition available.

+ Details

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- Details

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- Definition

Represents the deferred compensation plan investment income (loss) related to the mark-to-market of the investments treated as trading securities.

+ References

No definition available.

+ Details

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Namespace Prefix:	seb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the percentage of vesting after first year of service.

+ References

No definition available.

+ Details

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Namespace Prefix:	seb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the additional vesting percentage with each additional completed year of service, after the first year of service.

+ References

No definition available.

+ Details

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Namespace Prefix:	seb_
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Period Type:	duration

- Definition

Represents the number of deferred compensation plans.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable beyond one year (or the operating cycle, if longer).

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 17

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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- Details

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