Employee Incentive Plans (Details 2) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2011
Service-based vested and non-vested common shares and restricted stock units [Member]
Unrecognized gross compensation cost data
Unrecognized gross compensation costs	$ 5.1
Expected period (in years) over which the remaining gross compensation costs will be recognized
Unrecognized remaining compensation costs on nonvested awards	2.0
Performance Shares [Member]
Unrecognized gross compensation cost data
Unrecognized gross compensation costs	$ 5.3
Expected period (in years) over which the remaining gross compensation costs will be recognized
Unrecognized remaining compensation costs on nonvested awards	2.5

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph h
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition
Namespace Prefix:	us-gaap
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration