Net Income per Share (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions		3 Months Ended	9 Months Ended
	Oct. 21, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 16, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from EPS			0.7	0.3
Amount authorized under Stock Repurchase Program			$ 1,500,000,000
Available for repurchase under the Stock Repurchase Program			385,900,000
Aggregate cost		$ 12,159,000	$ 102,938,000	$ 69,613,000
Subsequent Event
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Available for repurchase under the Stock Repurchase Program	$ 135,300,000
Aggregate cost	$ 250,600,000
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from EPS			1.1	1.5
Class A Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amount authorized under Stock Repurchase Program					$ 250,000,000
Number of shares repurchased			4.0
Average purchase price (in dollars per share)			$ 25.85
Additional outstanding shares available in offering (up to)					2.00%
Class A Common Stock | Subsequent Event
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of shares repurchased	10.8
Average purchase price (in dollars per share)	$ 23.20
Class A Common Stock | Maximum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Share price (in dollars per share)					$ 26.50
Class A Common Stock | Minimum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Share price (in dollars per share)					$ 22.50