Stockholders' Equity - Narrative (Details) - USD ($) shares in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Nov. 08, 2018	Feb. 29, 2016
Class of Stock [Line Items]
Stock repurchase program, authorized amount							$ 1,000,000,000.0
Repurchase authorization increase	$ 416,700,000
Authorized and available for repurchase		$ 750,000,000		$ 750,000,000
Repurchases of common stock		(440,400,000)		(625,925,000)	$ (306,629,000)
Amortization expense from capitalized stock-based compensation		$ 6,600,000	$ 5,100,000	$ 18,100,000	$ 12,500,000
Common Stock
Class of Stock [Line Items]
Shares repurchased during period (in shares)		5.9		8.3
Subsequent Event
Class of Stock [Line Items]
Stock repurchase program, authorized amount						$ 1,100,000,000.0