Benefit Plans Benefit Plans - Defined Contribution Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Cost Recognized	$ 6,483	$ 1,895	$ 5,077
Employee Contributions Up To Three Percent [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Participant Contribution Percentage	3.00%
Employee Contributions Second Three Percent [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Participant Contribution Percentage	3.00%
Employee Contributions First Six Percent [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Participant Contribution Percentage	6.00%
Effective July 1, 2003 to March 31, 2009 [Member] | Employee Contributions Up To Three Percent [Member] | Subsequent to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	100.00%
Effective July 1, 2003 to March 31, 2009 [Member] | Employee Contributions Up To Three Percent [Member] | Prior to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	60.00%
Effective July 1, 2003 to March 31, 2009 [Member] | Employee Contributions Second Three Percent [Member] | Subsequent to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	60.00%
Effective July 1, 2003 to March 31, 2009 [Member] | Employee Contributions Second Three Percent [Member] | Prior to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	40.00%
Effective April 1, 2009 to December 31, 2010 [Member] | Employee Contributions Up To Three Percent [Member] | Prior to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	0.00%
Effective April 1, 2009 to December 31, 2010 [Member] | Employee Contributions Second Three Percent [Member] | Prior to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	0.00%
Effective April 1, 2009 to December 31, 2010 [Member] | Employee Contributions First Six Percent [Member] | Subsequent to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	30.00%
Effective January 1, 2011 to December 31, 2011 [Member] | Employee Contributions First Six Percent [Member] | Subsequent to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	55.00%
Effective January 1, 2011 to December 31, 2011 [Member] | Employee Contributions First Six Percent [Member] | Prior to July 1, 2003 Hire Date [Member]
Defined Contribution Plan [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent	25.00%