Long-Term Incentive Plan (Equity-Based Incentive Compensation Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	$ 2,843	$ 3,750
Allocation of LTIP expense on consolidated statements of income	2,843	3,750
Retention Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	185	190
Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	2,011	2,629
Equity Method [Member] | Retention Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	185	190
Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	832	1,121
G&A Expense [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on consolidated statements of income	2,505	3,657
Operating Expenses [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on consolidated statements of income	338	93
2009 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		1,549
2009 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		927
2009 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense		622
2010 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	930	1,304
2010 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	522	950
2010 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	408	354
2011 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	1,016	707
2011 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	743	562
2011 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	273	145
2012 Awards [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	712
2012 Awards [Member] | Equity Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	561
2012 Awards [Member] | Liability Method [Member]
Long Term Incentive Plan [Line Items]
Equity-based incentive compensation expense	$ 151