Employee Incentive Plans, Summary of Activity Table (Details) (USD $)	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
Non-Vested Common Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning Balance, Outstanding, shares	268,864
Beginning balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 27.91
Granted, shares	83,066	97,931
Weighted-Average Grant-Date Fair Value per Share, Granted	$ 47.07	$ 34.39
Vested, shares	(63,028)	(75,680)
Weighted-Average Grant-Date Fair Value per Share, Vested	$ 51.61	$ 52.92
Forfeited, shares	0
Weighted-Average Grant-Date Fair Value per Share, Forfeited	$ 0
Cancelled, Shares	0
Weighted-Average Grant-Date Fair Value per Share, Cancelled	$ 0
Ending Balance, Outstanding, shares	288,902
Ending balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 28.25
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning Balance, Outstanding, shares	7,872
Beginning balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 21.74
Granted, shares	2,182	2,362
Weighted-Average Grant-Date Fair Value per Share, Granted	$ 46.59	$ 36.23
Vested, shares	(3,314)	(686)
Weighted-Average Grant-Date Fair Value per Share, Vested	$ 16.83	$ 37.79
Forfeited, shares	0
Weighted-Average Grant-Date Fair Value per Share, Forfeited	$ 0
Cancelled, Shares	0
Weighted-Average Grant-Date Fair Value per Share, Cancelled	$ 0
Ending Balance, Outstanding, shares	6,740
Ending balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 32.20
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning Balance, Outstanding, shares	686,895
Beginning balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 26.84
Granted, shares	188,741	205,789
Weighted-Average Grant-Date Fair Value per Share, Granted	$ 46.65	$ 34.13
Vested, shares	(10,585)	(609)
Weighted-Average Grant-Date Fair Value per Share, Vested	$ 74.34	$ 31.02
Forfeited, shares	0
Weighted-Average Grant-Date Fair Value per Share, Forfeited	$ 0
Cancelled, Shares	(68,799)
Weighted-Average Grant-Date Fair Value per Share, Cancelled	$ 74.34
Ending Balance, Outstanding, shares	796,252
Ending balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 26.80

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

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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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- Definition

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

+ References

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- Definition

The 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 during the reporting period as a result of the occurrence of a terminating event specified in the contractual agreement of the plan.

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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).

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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).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

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-Name Statement of Financial Accounting Standard (FAS)

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-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.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

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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.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(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 Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(b)

-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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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(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 Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(b)

-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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-Section 50

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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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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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