Income Taxes - Earnings Before Income Taxes and Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings before income taxes:
United States	$ 634,515	$ 614,261	$ 520,282
Foreign	139,395	108,904	110,817
Total	773,910	723,165	631,099
Income tax expense:
Partnership UBT	2,986	5,363	8,027
Corporate subsidiaries:
Federal	18,079	291	7,957
State and local	803	1,064	661
Foreign	29,365	28,158	26,822
Current tax expense	51,233	34,876	43,467
Deferred tax (benefit)	1,877	(6,557)	1,330
Income tax expense	$ 53,110	$ 28,319	$ 44,797