Convertible Senior Notes (Narrative) (Details)			1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 01, 2017 $ / shares	Apr. 30, 2014 $ / shares shares	Jan. 31, 2017 $ / shares	Sep. 30, 2017 USD ($) shares	Jun. 30, 2014 USD ($)	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Amount used to repurchase stock						$ 574,957,000	$ 28,689,000
Convertible notes, long-term				$ 1,376,673,000		1,376,673,000			$ 0
Convertible notes				0		0			1,348,156,000
Temporary equity				0		0			79,495,000
Purchase From Accelerated Share Repurchase [Member]
Debt Instrument [Line Items]
Stock repurchased during period, value					$ 1,400,000,000
Senior Notes Due 2019 [Member]
Debt Instrument [Line Items]
Convertible debt				1,376,673,000		1,376,673,000		$ 1,440,000,000	1,348,156,000
Stated interest rate percentage								0.50%
Proceeds from convertible debt								$ 1,420,000,000
Payments for (proceeds from) hedge, investing activities								$ 82,600,000
Stock repurchased during period, value					1,500,000,000
Convertible debt, conversion ratio	0.0139061		0.011111
Debt instrument, face amount				1,000		$ 1,000
Convertible debt, conversion price (in dollars per share) | $ / shares	$ 71.91		$ 90
Repurchase price as a percent of principal amount						100.00%
Amortization of debt discount, effective interest method, percent						3.00%
Convertible notes, long-term				1,400,000,000		$ 1,400,000,000
Convertible notes									1,300,000,000
Deferred tax liability, equity component				8,200,000		8,200,000
Temporary equity				$ 0		$ 0			$ 79,495,000
Shares of common stock covered by note hedges (shares) | shares						16,000,000
Warrant transaction (shares) | shares		16,000,000
Adjustment to number of shares of common stock covered by note hedges and warrant transactions (shares) | shares				20,000,000
Strike price of warrants (in dollars per share) | $ / shares	$ 95.25	$ 120.0
Warrants exercised (shares) | shares						0
Privately Negotiated Transaction [Member]
Debt Instrument [Line Items]
Amount used to repurchase stock					$ 101,000,000