Represents the average period used to calculate performance goals.

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Represents the period for calculation of performance goals based on consolidated net income.

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Represents the period for calculation of performance goals based on subsidiaries net income.

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Represents 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 or when performance conditions met.

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Represents the number of years used in the calculation of total return to shareholders.

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

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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 cancelled in during the period.

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Represents the total 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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Represents the estimated fair value at grant date for nonvested equity-based awards on other than stock (or unit) option plans.

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Represents the high end of range of payout depending on achievement of the goals.

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Represents the low end of range of payout depending on achievement of the goals.

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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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The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

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

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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).

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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.

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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
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-Name Accounting Standards Codification
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-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)
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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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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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
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-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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-Name Accounting Standards Codification
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-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 period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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 SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14
-Section D
-Subsection 2

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Share-based compensation (Details 4) (USD $)	6 Months Ended	3 Months Ended	6 Months Ended			3 Months Ended	6 Months Ended			1 Months Ended		6 Months Ended	1 Months Ended		6 Months Ended
Share-based compensation (Details 4) (USD $)	Jun. 30, 2011 Long-term incentive plan (LTIP)	Jun. 30, 2011 LTIP linked to TRS	Jun. 30, 2011 LTIP linked to TRS	Jun. 30, 2010 LTIP linked to TRS	Mar. 31, 2010 LTIP linked to TRS	Jun. 30, 2011 LTIP linked to other performance conditions	Jun. 30, 2011 LTIP linked to other performance conditions	Jun. 30, 2010 LTIP linked to other performance conditions	Mar. 31, 2010 LTIP linked to other performance conditions	May 31, 2011 2011-2013 LTIP linked to TRS	May 12, 2011 2011-2013 LTIP linked to TRS	Jun. 30, 2011 2011-2012 LTIP	May 31, 2011 2011-2013 LTIP linked to other performance conditions	May 12, 2011 2011-2013 LTIP linked to other performance conditions	Jun. 30, 2011 2009-2011 LTIP	Jun. 30, 2011 2010-2012 LTIP
Share-based compensation
Payout low end of range (as a percent)	0.00%
Payout high end of range (as a percent)	200.00%
Period for calculating total return to shareholders (in years)			3
Average period used to calculate performance goals (in years)															2	2
Period for calculating performance goals based on average consolidated net income (in years)												3
Period for calculating performance goals based on average net income (in years)												3
LTIP linked to TRS and other performance conditions (in shares)
Outstanding, beginning of period (in shares)		200,735	126,782	36,198	132,588	273,550	161,310	24,131	184,535		475			712
Granted (in shares)		475	75,015	97,191		712	113,831	160,939
Cancelled						(81,908)	(81,908)
Forfeited (in shares)		(1,647)	(2,234)	(801)		(6,587)	(7,466)	(535)
Outstanding, end of period (in shares)		199,563	199,563	132,588	132,588	185,767	185,767	184,535	184,535		475			712
Total weighted-average grant-date fair value			$ 2,700,000	$ 2,200,000			$ 2,800,000	$ 3,000,000		$ 17,000			$ 19,000
Weighted-average grant-date fair value per share
Outstanding, beginning of period (in dollars per share)		$ 25.94	$ 20.33	$ 14.85	$ 20.42	$ 21.26	$ 18.66	$ 16.99	$ 18.69		$ 26.25			$ 26.25
Granted (in dollars per share)		$ 35.46	$ 35.46	$ 22.45		$ 26.25	$ 24.96	$ 18.95
Forfeited (in dollars per share)		$ 22.45	$ 22.45	$ 14.85		$ 18.95	$ 18.95	$ 16.99
Cancelled (in dollars per share)						$ 18.38	$ 18.38
Outstanding, end of period (in dollars per share)		$ 25.99	$ 25.99	$ 20.42	$ 20.42	$ 22.63	$ 22.63	$ 18.69	$ 18.69		$ 26.25			$ 26.25
Total weighted-average grant-date fair value			2,700,000	2,200,000			2,800,000	3,000,000		17,000			19,000
Risk-free interest rate (as a percent)			1.25%	1.30%
Expected life (in years)			3	3
Expected volatility (as a percent)			27.80%	27.90%
Range of expected volatility for Peer Group, minimum (as a percent)			21.20%	22.30%
Range of expected volatility for Peer Group, maximum (as a percent)			82.60%	52.30%
Grant date fair value (in dollars per share)		$ 35.46	$ 35.46	$ 22.45	$ 22.45						$ 35.46
Unrecognized compensation cost		$ 3,100,000	$ 3,100,000			$ 3,100,000	$ 3,100,000
Weighted-average period over which unrecognized compensation cost expected to be recognized (in years)		1.7	1.7			2.1	2.1