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Equity-Based Compensation (Narrative) (Details) (USD $)
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3 Months Ended | 12 Months Ended | 3 Months Ended | 12 Months Ended | 3 Months Ended | 0 Months Ended | 3 Months Ended | 12 Months Ended | ||||
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Mar. 31, 2012
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Mar. 31, 2011
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Dec. 31, 2011
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Mar. 31, 2012
Unvested Restricted Stock Units [Member]
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Dec. 31, 2011
Unvested Restricted Stock Units [Member]
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Mar. 31, 2012
2005 Equity Incentive Plan [Member]
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Sep. 30, 2009
Performance Stock Units [Member]
Y
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Mar. 31, 2012
Performance Stock Units [Member]
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Jan. 31, 2012
Performance Stock Units [Member]
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Mar. 31, 2012
Management Stock Purchase Plan [Member]
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Mar. 31, 2011
Management Stock Purchase Plan [Member]
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Dec. 31, 2011
Management Stock Purchase Plan [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||||||
| Maximum number of shares that may be issued under the Plan | 3,000,000 | |||||||||||
| Maximum number of shares that may be issued in connection with grants of incentive stock options and rights | 900,000 | |||||||||||
| Unamortized portion of compensation expense related to awards | $ 885,000 | |||||||||||
| Performance stock units outstanding | 905,000 | 280,000 | 295,000 | |||||||||
| Performance stock unit grant-date fair value | 12,643,000 | 4,152,000 | ||||||||||
| Performance stock unit vesting period, years | 3 | |||||||||||
| Performance stock unit conversion date fair value | 8,319,000 | |||||||||||
| Weighted average fair value of per unit awarded | $ 12.12 | $ 11.15 | ||||||||||
| Number of restricted stock units credited to participant accounts | 746,142 | 533,548 | 90,488 | 65,374 | 222,551 | 153,144 | ||||||
| Accrues interest | 2.00% | |||||||||||
| Disbursements of MSPP | $ 542,000 | $ 518,000 | ||||||||||