Income Taxes - Computed Amount and Differences in Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Pretax income	$ 455,273	$ 368,512	$ 392,345
Computed amount at statutory rate of 35%	159,346	128,979	137,321
State and local income tax (net of federal tax benefit)	5,841	4,070	5,033
Taxes on non-U.S. earnings-net of foreign tax credits	(24,914)	(6,666)	(11,663)
Effect of flow-through entities	192	(8,735)	(8,358)
U.S. business tax credits	(1,928)	(1,665)	(1,273)
Domestic activities production deduction	(8,516)	(9,043)	(6,521)
Deferred tax effect of foreign tax rate change	0	0	(2,636)
Capital loss on divestitures	(2,275)	(23,444)	0
Share-based payments	(6,844)	(6,520)	0
Valuation allowance	(361)	17,973	0
Impact of Tax Act	(100)	0	0
Other	(2,425)	2,454	(2,365)
Total provision for income taxes	$ 118,016	$ 97,403	$ 109,538
Statutory tax rate	35.00%	35.00%	35.00%