Employee Incentive Plans (Details 3) (USD $)	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010
Non-Vested Common Shares [Member]
Fair value of non-vested common shares, restricted stock units, and performance shares
Beginning Balance, Outstanding, shares	268,864
Beginning balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 27.91
Granted, shares	76,803	96,850
Weighted-Average Grant-Date Fair Value per Share, Granted	$ 47.19	$ 34.31
Vested, shares	(62,028)	(75,680)
Weighted-Average Grant-Date Fair Value per Share, Vested	$ 51.63	$ 52.92
Ending Balance, Outstanding, shares	283,639
Ending balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 27.95
Performance Shares [Member]
Fair value of non-vested common shares, restricted stock units, and performance shares
Beginning Balance, Outstanding, shares	686,895
Beginning balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 26.84
Granted, shares	186,918	205,789
Weighted-Average Grant-Date Fair Value per Share, Granted	$ 46.59	$ 34.13
Vested, shares	(10,585)	(609)
Weighted-Average Grant-Date Fair Value per Share, Vested	$ 74.34	$ 31.02
Cancelled, Shares	(68,799)
Weighted-Average Grant-Date Fair Value per Share, Cancelled	$ 74.34
Ending Balance, Outstanding, shares	794,429
Ending balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 26.74
Restricted Stock Units (RSUs) [Member]
Fair value of non-vested common shares, restricted stock units, and performance shares
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
Ending Balance, Outstanding, shares	6,740
Ending balance, Weighted-Average Grant-Date Fair Value per Share, Outstanding	$ 32.20

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

Share based compensation restricted stock restricted stock units and performance share activity.

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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

+ Details

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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).

+ 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)(c)
-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 2: 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.

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

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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.

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

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

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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.

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

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

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- Definition

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

+ References

+ Details

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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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