Employee Incentive Plans, Long term Incentive Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares authorized for issuance under Equity Incentive Plan	2,722,222
Number of common shares available for additional awards under Equity Incentive Plan	865,562
Non-cash compensation expense	$ 2.6	$ 2.5
Stock Options
Fully-vested options outstanding	20,791		20,791
Exercise price of options to purchase common stock	$ 80.01		$ 80.01
Remaining contractual life of options outstanding	4 years		4 years 3 months
Grant date fair value of options outstanding	$ 39.90		$ 39.90
Stock options granted	0
Stock options forfeited	0
Stock options exercised	0
Vested Stock
Common shares withheld and canceled	35,838	45,128
Fabricated Products
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash compensation expense	0.6	0.7
All Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash compensation expense	2.0	1.8
Non-vested common shares
Summary of Activity
Outstanding at December 31, 2012, Shares	158,684
Outstanding at December 31, 2012, Weighted-Average Grant-Date Fair Value per Share	$ 42.47
Granted, shares	57,190	72,859
Granted, Weighted-Average Grant-Date Fair Value per Share	$ 57.54	$ 44.46
Vested, shares	(65,646)	(119,413)
Vested, Weighted-Average Grant-Date Fair Value per Share	$ 40.29	$ 21.09
Forfeited, shares	0
Forfeited, Weighted-Average Grant-Date Fair Value per Share	$ 0.00
Canceled, Shares	0
Canceled, Weighted-Average Grant-Date Fair Value per Share	$ 0
Outstanding at March 31, 2013, Shares	150,228
Outstanding at March 31, 2013, Weighted-Average Grant-Date Fair Value per Share	$ 49.16
Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common share received by the employee on vesting of restricted stock unit	1
Summary of Activity
Outstanding at December 31, 2012, Shares	5,183
Outstanding at December 31, 2012, Weighted-Average Grant-Date Fair Value per Share	$ 43.99
Granted, shares	2,333	2,486
Granted, Weighted-Average Grant-Date Fair Value per Share	$ 57.54	$ 44.46
Vested, shares	(2,311)	(3,375)
Vested, Weighted-Average Grant-Date Fair Value per Share	$ 42.74	$ 25.77
Forfeited, shares	0
Forfeited, Weighted-Average Grant-Date Fair Value per Share	$ 0
Canceled, Shares	0
Canceled, Weighted-Average Grant-Date Fair Value per Share	$ 0
Outstanding at March 31, 2013, Shares	5,205
Outstanding at March 31, 2013, Weighted-Average Grant-Date Fair Value per Share	$ 50.62
Service-based non-vested common shares and restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash compensation expense	1.7	1.7
Unrecognized gross compensation costs, by award type	5.2
Expected period (in years) over which the remaining gross compensation costs will be recognized, by award type	2 years
Performance shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance award vesting period, years	3 years
Non-cash compensation expense	0.9	0.8
Unrecognized gross compensation costs, by award type	$ 9.3
Expected period (in years) over which the remaining gross compensation costs will be recognized, by award type	2 years 6 months
Summary of Activity
Outstanding at December 31, 2012, Shares	583,950
Outstanding at December 31, 2012, Weighted-Average Grant-Date Fair Value per Share	$ 41.78
Granted, shares	167,312	211,900
Granted, Weighted-Average Grant-Date Fair Value per Share	$ 57.54	$ 44.46
Vested, shares	(32,312)	(7,952)
Vested, Weighted-Average Grant-Date Fair Value per Share	$ 34.13	$ 18.89
Forfeited, shares	0
Forfeited, Weighted-Average Grant-Date Fair Value per Share	$ 0
Canceled, Shares	(157,876)
Canceled, Weighted-Average Grant-Date Fair Value per Share	$ 34.13
Outstanding at March 31, 2013, Shares	561,074
Outstanding at March 31, 2013, Weighted-Average Grant-Date Fair Value per Share	$ 49.08

Number of common share received by the employee on vesting of restricted stock unit.

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Share based compensation arrangement by share based payment award equity instruments other than options cancelled in Period.

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No definition available.

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- Definition

Share based compensation arrangement by share based payments award equity instruments other than options cancelled in period weighted average grant date fair value.

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No definition available.

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- Definition

Represents the expense 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

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

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

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- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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-Paragraph 2

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ 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

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- Definition

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

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- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(1)

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

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

+ References

No definition available.

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Number of share options (or share units) exercised during the current period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-02.28,29)

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-Section 04

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-Name Regulation S-X (SX)

-Number 210

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