New Accounting Standards (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service cost	$ 2,700,000	$ 2,600,000	$ 5,500,000	$ 5,300,000
Restricted Cash	0		0		$ 0
Net periodic benefit cost	1,000,000	2,000,000	2,200,000	3,900,000
Income tax expense	6,000,000	2,900,000	18,500,000	5,100,000
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax expense	3,400,000	9,600,000	5,500,000	25,500,000
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net benefit cost components other than service cost	1,700,000	$ 600,000	3,300,000	$ 1,400,000
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating leases, Future minimum payments due	$ 71,300,000		$ 71,300,000		$ 79,100,000