Share-Based Payments (Details Textual)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Share-Based Payments (Textual) [Abstract]
Shares issued under ESPP	106,000	185,000
Number of stock option	0	0
Market stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted in connection with annual awards	286,000	363,000
Market stock units [Member] | Attainment of Performance Criteria [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted in connection with annual awards	217,000	347,000
Cash settled performance shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted in connection with annual awards	310,000	467,000
Cash settled performance shares [Member] | Attainment of Performance Criteria [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted in connection with annual awards	245,000	379,000
Performance vested restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted in connection with annual awards		1,000
Performance vested restricted stock units [Member] | Attainment of Performance Criteria [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted in connection with annual awards	0	0