Description of Business and Accounting Policies - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) Customer	Jun. 30, 2018	Jun. 30, 2019 USD ($) Customer	Jun. 30, 2018	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($) Customer
Description of Business and Accounting Policies [Line Items]
Number of customers, exceeds 10% of total accounts receivable | Customer	0		0			1
Revenue derived from foreign operations	5.00%	6.00%	5.00%	6.00%
Operating lease, right-of-use assets	$ 37.4		$ 37.4		$ 38.3	$ 0.0
Operating lease, liability	$ 44.6		$ 44.6		$ 46.2
Verizon Communications Inc. [Member]
Description of Business and Accounting Policies [Line Items]
Accounts receivable from one customer greater than 10%, percentage						18.00%