Share Incentive Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Compensation information
Compensation Expense	$ 24,832	$ 21,177	$ 18,875
Compensation Capitalized	2,128	2,305	2,141
Compensation Equity	26,960	23,482	21,016
Dividends Incurred	1,183	1,320	1,472
Restricted shares [Member]
Compensation information
Compensation Expense	8,014	8,041	8,603
Compensation Capitalized	922	1,061	1,178
Compensation Equity	8,936	9,102	9,781
Dividends Incurred	949	1,121	1,334
Long Term Investment Plan Units [Member]
Compensation information
Compensation Expense	5,004	3,344	2,334
Compensation Capitalized	303	297	190
Compensation Equity	5,307	3,641	2,524
Dividends Incurred	234	199	138
Employee Stock Option [Member]
Compensation information
Compensation Expense	10,970	8,711	6,707
Compensation Capitalized	782	834	714
Compensation Equity	11,752	9,545	7,421
Dividends Incurred	0	0	0
Employee Share Purchase Plan Discount [Member]
Compensation information
Compensation Expense	844	1,081	1,231
Compensation Capitalized	121	113	59
Compensation Equity	965	1,194	1,290
Dividends Incurred	$ 0	$ 0	$ 0

This element represents the amount of recognized equity-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized). Alternate captions include the words "stock-based compensation".

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 20

-Section 55

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64

-Subparagraph 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

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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 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 20

-Section 55

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6576910&loc=d3e11149-113907

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 39

-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.

+ Details

- 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+ Details