Income Taxes - Earnings Before Income Taxes and Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings before income taxes:
United States	$ 520,282	$ 493,311	$ 471,813
Foreign	110,817	115,310	92,438
Total	631,099	608,621	564,251
Income tax expense:
Partnership UBT	6,855	9,356	4,403
Corporate subsidiaries:
Federal	2,576	6,321	7,032
State and local	539	1,326	2,318
Foreign	26,822	31,625	26,139
Current tax expense	36,792	48,628	39,892
Deferred tax (benefit)	1,330	(10,846)	(3,063)
Income tax expense	$ 38,122	$ 37,782	$ 36,829