Shareholders' Deficit - Additional Information (Detail) - USD ($)		1 Months Ended	2 Months Ended	3 Months Ended				9 Months Ended
	May. 07, 2014	Feb. 28, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Feb. 03, 2014	Jul. 30, 2012
Stockholders Equity [Line Items]
Dividends paid				$ 0	$ 0			$ 0	$ 30,400,000
Dividends received primarily relating to forward transactions				0	0			$ 0	3,400,000
Share repurchase program authorized amount											$ 1,500,000,000	$ 1,000,000,000
Share repurchase program expiration date								Jun. 30, 2017
Accumulated deficit				(410,800,000)				$ (410,800,000)		$ (665,400,000)
Additional paid-in-capital				436,300,000				436,300,000		$ 409,100,000
Non-cash forward transaction issuance costs							$ 35,800,000
Non-cash interest expense				$ 1,600,000	1,600,000			4,800,000	4,200,000
Repurchase of common stock, amount	$ 266,000,000							$ 10,700,000	1,278,400,000
Repurchase of common stock, shares			4,300,000	0				0
Amounts reclassified from accumulated other comprehensive income (loss) to income, tax expense unrealized gain (loss) on available-for-sale investments					2,400,000			$ 800,000	3,400,000
Foreign Currency Translation Adjustments [Member]
Stockholders Equity [Line Items]
Other comprehensive income (loss) before reclassifications, Tax expense (benefits)				$ (2,700,000)	(800,000)			(7,000,000)	700,000
Unrealized Gain (Loss) on Derivatives [Member]
Stockholders Equity [Line Items]
Other comprehensive income (loss) before reclassifications, Tax expense (benefits)				(300,000)	500,000			200,000	200,000
Amounts reclassified from accumulated other comprehensive income (loss) to income, tax expense (benefits) unrealized gain (loss) on derivatives				100,000				(100,000)
Unrealized Gain (Loss) on Available-For-Sale Investments [Member]
Stockholders Equity [Line Items]
Other comprehensive income (loss) before reclassifications, Tax expense (benefits)					$ (2,500,000)			$ (1,000,000)	$ (3,500,000)
Capped call transactions [Member]
Stockholders Equity [Line Items]
Capped call transactions with financial institutions		$ 123,800,000
Capped call transactions price per common share		$ 120.79
Increase (decrease) in additional paid-in capital, other							(123,800,000)
Capped call transactions [Member] | Convertible Notes [Member]
Stockholders Equity [Line Items]
Convertible notes initial conversion price		$ 86.28
Repurchase Agreement 2014 [Member]
Stockholders Equity [Line Items]
Agreement expiration date								Jun. 30, 2014
Prepaid forward share repurchase transactions [Member]
Stockholders Equity [Line Items]
Forward share repurchase transactions amount		$ 685,800,000					$ 685,800,000
Share repurchase transaction, shares to be purchased		9,900,000					9,900,000
Settlement date of forward transactions								Aug. 15, 2019
Accumulated deficit							$ (653,900,000)
Additional paid-in-capital							$ (31,900,000)
Average cost per share of shares repurchased							$ 69.02
Share repurchase program, remaining authorized capacity				$ 232,900,000				$ 232,900,000
Open market purchases [Member]
Stockholders Equity [Line Items]
Repurchase of common stock, shares					0	9,800,000
Shares repurchased aggregate cost						$ 581,300,000
Average cost per share of shares repurchased						$ 59.41