Share Based Compensation (Details 1) (USD $) In Thousands, except Share data	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010
Summary of restricted stock units
Outstanding at January 1, 2011 , Shares	50,032
Outstanding at January 1, 2011, Weighted Average Grant Date Fair Value	$ 58.40
Granted, Non-Vested Shares	68,727	3,239
Granted, Weighted Average Grant Date Fair Value	$ 37.83	$ 30.88
Vested, Shares	(9,474)	(16,358)
Vested, Weighted Average Grant Date Fair Value	$ 56.76
Outstanding as June 30, 2011, Shares	109,285
Outstanding as of June 30, 2011, Weighted Average Grant Date Fair Value	$ 45.61
Summary of Nonvested and Vested Restricted Stock Units
Granted, Non-Vested Shares	68,727	3,239
Granted, Weighted Average Grant Date Fair Value	$ 37.83	$ 30.88
Vested, Shares	(9,474)	(16,358)
Vested shares, total fair value	$ 370	$ 474
Nonvested Restricted Stock Units RSU [Member]
Summary of restricted stock units
Outstanding at January 1, 2011 , Shares	125,754
Outstanding at January 1, 2011, Weighted Average Grant Date Fair Value	$ 29.88
Granted, Non-Vested Shares	107,673	159,606
Granted, Weighted Average Grant Date Fair Value	$ 37.94	$ 30.24
Vested, Shares	(23,035)
Vested, Weighted Average Grant Date Fair Value	$ 30.57
Issuance of dividend equivalents	0
Cancelled	0
Outstanding as June 30, 2011, Shares	210,392
Outstanding as of June 30, 2011, Weighted Average Grant Date Fair Value	$ 33.93
Summary of Nonvested and Vested Restricted Stock Units
Granted, Non-Vested Shares	107,673	159,606
Granted, Weighted Average Grant Date Fair Value	$ 37.94	$ 30.24
Vested, Shares	(23,035)
Vested Restricted Stock Units RSU [Member]
Summary of restricted stock units
Outstanding at January 1, 2011, Vested RSUs and Total RSUs	588,068
Granted, Non-Vested Shares	0
Vested, Shares	23,035	23,564
Issuance of dividend equivalents	13,494
Cancelled	(8,448)
Outstanding as of June 30, 2011,Vested RSUs and Total RSUs	616,149
Summary of Nonvested and Vested Restricted Stock Units
Granted, Non-Vested Shares	0
Vested, Shares	23,035	23,564
Vested shares, total fair value	$ 897	$ 740
Restricted Stock Units (RSUs) [Member]
Summary of restricted stock units
Outstanding at January 1, 2011, Vested RSUs and Total RSUs	713,822
Granted, Non-Vested Shares	107,673
Vested, Shares	0
Issuance of dividend equivalents	13,494
Cancelled	(8,448)
Outstanding as of June 30, 2011,Vested RSUs and Total RSUs	826,541
Summary of Nonvested and Vested Restricted Stock Units
Granted, Non-Vested Shares	107,673
Vested, Shares	0

Schedule of Share Based Compensation Restricted Stock Units Award Activity.

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The number of restricted stock units that were cancelled to cover the statutory minimum tax withholding on share based compensation distributions made in cash or shares of common stock.

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The number of restricted stock units that were issued as dividend equivalents during the period. Restricted stock units issued as dividend equivalents are vested upon issuance.

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The number of vested or total 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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Summary of nonvested and vested restricted stock units.

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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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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.

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- Definition

The total fair value of equity-based awards 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.

+ References

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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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