Stockholders' Equity - Repurchase Program (Details)					1 Months Ended	9 Months Ended		17 Months Ended	20 Months Ended
	Sep. 07, 2017 shares	Aug. 07, 2017 USD ($) $ / shares shares	Jul. 27, 2017 USD ($)	Feb. 04, 2016 USD ($)	Sep. 07, 2017 $ / shares	Sep. 30, 2017 USD ($) transaction shares	Sep. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) shares	Nov. 01, 2017 USD ($)	Aug. 03, 2017 USD ($)
Class of Stock [Line Items]
Shares repurchased (in shares) | shares	263,012	1,491,647				2,854,959			4,114,104
Accelerated Share Repurchases, Initial Price Paid Per Share | $ / shares		$ 142.46
Repurchase of common stock						$ 402,392,000	$ 35,492,000
ASR price paid per share (in dollars per share) | $ / shares					$ 142.48
Number of transactions | transaction						2
Common Stock
Class of Stock [Line Items]
Stock repurchase program, approved amount				$ 500,000,000
Stock repurchase program, authorized time period				18 months
Increase in authorized amount to be repurchased			$ 250,000,000
Period in force, extension of original period			18 months
Remaining authorized repurchase amount			$ 510,000,000
Repurchase agreements
Class of Stock [Line Items]
Shares repurchased								$ 590,100,000	$ 590,100,000
Repurchase of common stock		$ 250,000,000				$ 402,400,000
Repurchase agreements | Common Stock
Class of Stock [Line Items]
Stock repurchase program, approved amount											$ 250,000,000
Subsequent Event | Common Stock
Class of Stock [Line Items]
Stock repurchase program, approved amount										$ 1,100,000,000.0
Increase in authorized amount to be repurchased										$ 350,000,000