Share-Based Compensation and Equity - Director Deferred Shares Activity (Details) (Director Deferred Shares [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Director Deferred Shares [Member]
Director Deferred Shares
Unvested, Shares, Beginning balance	14
Unvested, Weighted-average grant-date fair value, Beginning balance	$ 33.28
Vested, Shares	(26)
Vested, Weighted-average grant-date fair value	$ 33.61
Granted, Shares	31
Granted, Weighted-average grant-date fair value	$ 33.98	$ 33.28	$ 25.52
Unvested, Shares, Ending balance	19	14
Unvested, Weighted-average grant-date fair value, Ending balance	$ 33.98	$ 33.28
Vested, Shares, Ending balance	96
Vested Shares, Weighted Average grant-date fair value, ending balance	$ 33.88
Outstanding, Shares, Ending balance	115
Outstanding Shares, Weighted Average grant-date fair value, ending balance	$ 33.90
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Released Intrinsic Value	$ 247	$ 0	$ 158
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 887	$ 819	$ 843