Retirement Benefit Plan (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Retirement Benefit Plan (Textual) [Abstract]
Description of defined contribution pension and other postretirement plans	(i) 100% of each participant’s first 1% of contributions plus (ii) 50% of each participant’s contributions up to the next 5% of eligible compensation
Recognized matching contributions from retirement benefit plans	$ 8.7	$ 3.9	$ 4.4

- Definition

Description of the terms and benefits provided by the employer's defined contribution plans. A defined contribution plan provides benefits in return for services rendered, provides an individual account for each participant, and has terms that specify how contributions to the individual's account are to be determined rather than the amount of benefits the individual is to receive. Under a defined contribution pension plan, the benefits a participant will receive depend solely on the amount contributed to the participant's account, the returns earned on investments of those contributions, and forfeitures of other participants' benefits that may be allocated to such participant's account. A description of the plan(s) including employee groups covered, the basis for determining contributions, and the nature and effects of significant matters affecting comparability of information for all periods presented.

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