Stockholders' Equity - Repurchase Program (Details) - USD ($)				3 Months Ended	9 Months Ended		32 Months Ended
		Jul. 27, 2017	Feb. 04, 2016	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Jul. 17, 2018	Nov. 01, 2017
Class of Stock [Line Items]
Repurchase of common stock	[1]				$ 380,651,000	$ 402,392,000
Common Stock
Class of Stock [Line Items]
Stock repurchase program, approved amount			$ 500,000,000						$ 1,600,000,000.0
Stock repurchase program, authorized time period			18 months
Increase in authorized amount to be repurchased		$ 250,000,000						$ 500,000,000	$ 350,000,000
Period in force, extension of original period		18 months
Remaining authorized repurchase amount				$ 629,200,000	$ 629,200,000		$ 629,200,000
Repurchase agreements
Class of Stock [Line Items]
Shares repurchased							$ 970,800,000
Shares repurchased (in shares)				0	1,896,106		6,010,210
Repurchase of common stock					$ 380,700,000

[1] Reflects the impact of the Company's adoption of Accounting Standards Update 2016-18, "Statement of Cash Flows (Topic 230)", which was adopted by the Company on January 1, 2018 and applied retrospectively to results for 2017. The adoption of Topic 230 resulted in the statement of cash flows presenting the changes in the total of cash, cash equivalents and restricted cash. As a result, the Company will no longer present transfers between cash and cash equivalents and restricted cash in the statement of cash flows.