Stockholders' Equity - Narrative (Details) - USD ($) shares in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2018	Feb. 28, 2014	Mar. 31, 2018	Mar. 31, 2017	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		$ (62,000,000)	(19,785,000)	$ (72,467,000)
Amortization expense from capitalized stock-based compensation			$ 5,600,000	$ 3,500,000
Common Stock [Member]
Class of Stock [Line Items]
Shares repurchased during period (in shares)			0.3