Acquisitions and Divestitures - Divestitures (Details) - USD ($)		3 Months Ended			9 Months Ended
	Oct. 31, 2017	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense		$ 26,889,000		$ 30,019,000	$ 87,678,000	$ 88,160,000
Faure Herman subsidiary | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of business	$ 21,800,000
Gain on sale of businesses - net			$ 9,300,000
Income tax expense			$ 0