Goodwill and Other Intangible Assets (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 03, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 113,200,000		$ 113,200,000			$ 54,600,000
Finite-lived intangible assets acquired			70,500,000
Impairment of intangible assets	0	$ 0	0	$ 0
Amortization expense of intangible assets	11,300,000	$ 8,200,000	22,900,000	$ 14,000,000.0
Periscope Acquisition
Goodwill [Line Items]
Goodwill	$ 58,600,000		$ 58,600,000		$ 58,600,000