Long-Term Incentive Plan (Equity-Based Incentive Compensation Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	$ 4,165	$ 5,267	$ 7,008	$ 9,017
Allocation of LTIP expense on consolidated statements of income	4,165	5,267	7,008	9,017
Retention Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	158	118	343	308
Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	3,066	3,375	5,077	6,004
Equity Method [Member] | Retention Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	158	118	343	308
Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	1,099	1,892	1,931	3,013
G&A Expense [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on consolidated statements of income	3,715	4,663	6,220	8,320
Operating Expenses [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on consolidated statements of income	450	604	788	697
2009 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		3,891		5,440
2009 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		2,308		3,235
2009 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		1,583		2,205
2010 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	2,425	552	3,355	1,856
2010 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	1,655	387	2,177	1,337
2010 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	770	165	1,178	519
2011 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	866	706	1,882	1,413
2011 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	684	562	1,427	1,124
2011 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	182	144	455	289
2012 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	716		1,428
2012 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	569		1,130
2012 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	$ 147		$ 298