New Accounting Standards (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service cost	$ 2,600,000	$ 2,500,000	$ 8,100,000	$ 7,800,000
Restricted Cash	0		0		$ 0
Net periodic benefit cost	800,000	1,400,000	3,000,000	5,300,000
Income tax expense	8,000,000	14,000,000	26,500,000	19,100,000
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax expense	7,700,000	4,800,000	13,200,000	30,300,000
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net benefit cost components other than service cost	1,800,000	$ 1,100,000	5,100,000	$ 2,500,000
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating leases, Future minimum payments due	$ 67,000,000		$ 67,000,000		$ 79,100,000