Foreign Operations (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Foreign operations data
Revenues	$ 304,900,000	$ 304,400,000	$ 300,500,000	$ 299,400,000	$ 300,500,000	$ 298,800,000	$ 297,500,000	$ 305,300,000	$ 1,209,200,000	$ 1,202,100,000	$ 1,175,100,000
Foreign Operations (Textual) [Abstract]
Maximum percentage of consolidated revenues derive from any individual foreign country									10.00%
Percentage of company's identifiable assets	10.00%								10.00%
Assets of Continuing Operations	$ 8,937,600,000				7,994,000,000.0				$ 8,937,600,000	7,994,000,000.0	7,318,900,000
Foreign [Member]
Foreign operations data
Revenues									374,900,000	331,100,000	333,500,000
Foreign Operations (Textual) [Abstract]
Assets of Continuing Operations	3,438,600,000				2,624,500,000				3,438,600,000	2,624,500,000	2,470,900,000
United States [Member]
Foreign operations data
Revenues									834,300,000	871,000,000.0	841,600,000
Foreign Operations (Textual) [Abstract]
Assets of Continuing Operations	$ 5,499,000,000.0				$ 5,369,500,000				$ 5,499,000,000.0	$ 5,369,500,000	$ 4,848,000,000.0