Long-Term Incentive Plan (Equity-Based Incentive Compensation Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	$ 20,641	$ 19,358	$ 24,245
G&A Expense [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	20,463	19,204	23,937
Operating Expenses [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	178	154	308
Time-Based Awards [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	2,818	2,252	1,199
2013 Awards [Member] | Performance Shares [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	0	0	10,658
2014 Awards [Member] | Performance Shares [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	28	7,928	7,471
2015 Awards [Member] | Performance Shares [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	6,645	4,874	4,917
2016 Awards [Member] | Performance Shares [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	6,125	4,304	0
2017 Awards [Member] | Performance Shares [Member]
Long Term Incentive Plan [Line Items]
Allocation of LTIP expense on Consolidated Statements of Income	$ 5,025	$ 0	$ 0