Convertible Notes and Long-term Debt Obligations - 1.50% Convertible Senior Notes and Bond Hedge and Warrant Transactions - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended		1 Months Ended
	Mar. 31, 2014	Dec. 31, 2014 D	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2014	May 31, 2013
Debt Instrument [Line Items]
Aggregate principal amount of Notes		$ 659,800,000	$ 659,800,000	$ 660,000,000
Debt, interest expense			3,200,000
Coupon interest expense			16,200,000
Debt instrument convertible consecutive trading days		30 days
Debt instrument convertible trading days		20
Percentage of repurchase price is equal to principal amount of convertible notes			100.00%
Debt conversion, converted instrument, amount			82,800,000
Debt instrument, effective interest rate		4.29%	4.29%
Amortization of debt discount			69,734,000	9,143,000
Payment for purchase of common stock	5,600,000
Common stock purchase price	$ 359.87
Hedge transactions	524,700,000
Shares issued under warrants		3,090,111	3,090,111
Exercise price of warrant		$ 7.54	$ 7.54
Proceeds from issuance of warrants			389,160,000	120,318,000
Common stock price to conversion price, percentage		130.00%
Difference between principal amount and carrying value of Notes		58,196,000	58,196,000
Warrants [Member]
Debt Instrument [Line Items]
Hedge transactions					78,700,000
Proceeds from issuance of warrants					50,800,000
1.50% Convertible senior notes due 2018 [Member]
Debt Instrument [Line Items]
Aggregate principal amount of Notes		659,800,000	659,800,000			660,000,000
Debt instrument interest rate						1.50%
Debt instrument maturity year			2018
Proceeds from convertible senior notes, net of underwriting discounts and offering costs						648,000,000
Debt issuance costs						12,000,000
Debt payment due dates			payable semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2013
Debt, interest expense			2,000,000	1,200,000
Coupon interest expense			9,800,000	5,900,000
Convertible principal amount			1,000
Convertible instrument, shares issued			8.0306
Debt instrument convertible, conversion price per share		$ 124.52	$ 124.52
Debt instrument convertible trading days			5
Debt instrument convertible, percentage of conversion price		130.00%	130.00%
Average percentage of closing sale price of common stock			98.00%
Amortization of debt discount			15,500,000	9,100,000
Net carrying value of notes		601,600,000	601,600,000
Remaining discounts on bond		58,200,000	58,200,000
Remaining amortization period of discount			3 years 2 months 12 days
Payment for purchase of common stock		5,300,000	5,300,000
Common stock purchase price		$ 124.52	$ 124.52
Hedge transactions			177,500,000
Shares issued under warrants		5,300,000	5,300,000
Exercise price of warrant		$ 184.48	$ 184.48
Notes carrying value		601,600,000	601,600,000
Difference between principal amount and carrying value of Notes		58,200,000	58,200,000
Excess of if-converted value over principal amount			518,700,000
1.50% Convertible senior notes due 2018 [Member] | Warrants [Member]
Debt Instrument [Line Items]
Proceeds from issuance of warrants			$ 120,300,000
1.50% Convertible senior notes due 2018 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument convertible consecutive trading days			20 days
1.50% Convertible senior notes due 2018 [Member] | Minimum [Member] | Warrants [Member]
Debt Instrument [Line Items]
Conversion price per share		$ 124.52	$ 124.52
1.50% Convertible senior notes due 2018 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument convertible consecutive trading days			30 days
1.50% Convertible senior notes due 2018 [Member] | Maximum [Member] | Warrants [Member]
Debt Instrument [Line Items]
Conversion price per share		$ 184.48	$ 184.48