Long-Term Incentive Plan (Equity-Based Incentive Compensation Expense) (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	$ 2,734	$ 4,573	$ 11,751	$ 11,482
Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	1,735	2,971	7,739	7,887
Equity Method [Member] | 2008 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		1,930		4,855
Equity Method [Member] | 2009 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	600	350	3,835	1,050
Equity Method [Member] | 2010 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	387	473	1,724	1,382
Equity Method [Member] | 2011 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	578		1,702
Equity Method [Member] | Retention Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	170	218	478	600
Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	999	1,602	4,012	3,595
Liability Method [Member] | 2007 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense				6
Liability Method [Member] | 2008 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		1,057		2,326
Liability Method [Member] | 2009 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	657	358	2,862	818
Liability Method [Member] | 2010 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	189	187	708	445
Liability Method [Member] | 2011 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	153		442
G&A Expense [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	2,375	3,975	10,696	10,031
Operating Expense [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	359	598	1,055	1,451
2007 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense				6
2008 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		2,987		7,181
2009 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	1,257	708	6,697	1,868
2010 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	576	660	2,432	1,827
2011 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	731		2,144
Retention Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	$ 170	$ 218	$ 478	$ 600