Stock-Based Compensation - Narrative (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of award vesting types	3
Cash Liability for Performance-Based Units	$ 0
Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	0	0.1
Stock-based compensation, maximum number of unvested shares	462,000
Market Based Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	0	0
Stock-based compensation, maximum number of unvested shares	226,000
Vesting period	8 years
Service Based Award [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	0.1	0.1
Vesting period	4 years
Expiration period	8 years
Options issued	13,000	0
Deferred Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of shares vested in lieu of directors fees at the grant date	100.00%
Portion of Director fees matched to deferred stock units	25.00%
Vesting period of deferred stock	1 year
Minimum age required for meeting directors fees deferred vest criteria	65
Deferred Stock Units [Member] \| Director [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued to non-employee individual	2,000	2,000
Deferred stock units, performance-based stock units and restricted stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 0.2	$ 0.3

Cash Liability for Performance-Based Units

No definition available.

Name:	sfe_CashLiabilityforPerformanceBasedUnits
Namespace Prefix:	sfe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum age required for meeting directors fees deferred vest criteria.

+ References

No definition available.

+ Details

Name:	sfe_MinimumAgeRequiredForMeetingDirectorsFeesDeferredVestCriteria
Namespace Prefix:	sfe_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of shares vested in lieu of directors fees at the grant date.

+ References

No definition available.

+ Details

Name:	sfe_PercentageOfSharesVestedInLieuOfDirectorsFeesAtGrantDate
Namespace Prefix:	sfe_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Portion of director fees matched to deferred stock units.

+ References

No definition available.

+ Details

Name:	sfe_PortionOfDirectorFeesMatchedToDeferredStockUnits
Namespace Prefix:	sfe_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award equity instruments maximum number of unvested shares.

+ References

No definition available.

+ Details

Name:	sfe_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsMaximumNumberOfUnvestedShares
Namespace Prefix:	sfe_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Number of Award Vesting Types

+ References

No definition available.

+ Details

Name:	sfe_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofAwardVestingTypes
Namespace Prefix:	sfe_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Share based compensation arrangement by share based payment deferred award vesting period.

+ References

No definition available.

+ Details

Name:	sfe_ShareBasedCompensationArrangementByShareBasedPaymentDeferredAwardVestingPeriod
Namespace Prefix:	sfe_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

No definition available.

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of shares issued pursuant to the terms of a deferred compensation arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of share instruments newly issued under a share-based compensation plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=sfe_DeferredStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=sfe_MarketBasedAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=sfe_RestrictedStockUnitAndPerformanceStockUnitAndDeferredStockUnitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=sfe_ServiceBasedAwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: