Long-term Incentive Compensation Plans (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Holding units purchased in period	1.3	1.9
Dollar amount paid for holding units acquired	$ 31,000	$ 39,700
Open-market purchases of holding units	1.2	1.8
Dollar amount paid for open-market purchases of holding units	$ 27,800	$ 38,100
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued upon options exercised (in units)	0.3	0.1
Proceeds from stock options exercised	$ 4,468	$ 1,457
Employees and Eligible Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted holding unit awards to employees (in units)	1.1	0.3