Employee Incentive Plan (Share-Based Compensation Expense Schedule) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share Based Compensation Expense [Line Items]
Interest of non-controlling partners in share-based compensation	$ 1,166	$ 1,722	$ 3,152	$ 2,716
Amount of related income tax benefit recognized in income	690	306	1,848	887
General and Administrative Expense [Member]
Share Based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	2,610	2,233	7,157	4,473
Operating Expense [Member]
Share Based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	421	316	980	640
Total Amount Charged To Income [Member]
Share Based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	$ 3,031	$ 2,549	$ 8,137	$ 5,113