Employee Incentive Plan (Share-Based Compensation Expense Schedule) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share Based Compensation Expense [Line Items]
Interest of non-controlling partners in share-based compensation	$ 1,235	$ 1,338	$ 4,387	$ 4,054
Amount of related income tax benefit recognized in income	686	459	2,534	1,347
General and Administrative Expense [Member]
Share Based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	2,664	2,272	9,821	6,746
Operating Expense [Member]
Share Based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	423	310	1,403	949
Total Amount Charged To Income [Member]
Share Based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	$ 3,087	$ 2,582	$ 11,224	$ 7,695