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0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Additional Information (Detail) $ / shares in Units, shares in Millions	1 Months Ended	9 Months Ended
	May 31, 2017 USD ($) d $ / shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($)
Debt Instrument [Line Items]
Net proceeds from the debt offering		$ 389,233,000
Sales of warrants		58,880,000
Warrants, issuance costs		200,000
Deferred income tax benefit		$ 9,125,000	$ 165,000
0.25% Convertible Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.25%
Debt instrument, maturity date		Jun. 01, 2022
Debt instrument, payment terms		The interest rates are fixed at 0.25% per annum and are payable semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2017.
Net proceeds from the debt offering	$ 389,200,000
Principal amount of each convertible note	$ 1,000
Debt instrument, conversion ratio	10.5519
Debt instrument, conversion price per share \| $ / shares	$ 94.77
Debt Instrument, Redemption Price, Percentage	100.00%
Debt Instrument, Redemption, Description		Repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.
Carrying amount of equity component	$ 106,000,000
Debt instrument, effective interest rate	6.95%
Debt issuance costs	$ 10,800,000
Number of common shares to be repurchased under convertible note hedge transactions with certain counterparties \| shares		4.2
Hedging option strike price per common stock \| $ / shares		$ 94.77
Cost of convertible note hedge transactions		$ 78,900,000
Warrants expected to settle, description		The warrants are expected to settle three business days from each trading day commencing on September 1, 2022 and ending on the 79th trading day thereafter.
Settlement period of warrants excess price over strike price		3 days
Warrants expected to settle, commencement date		Sep. 01, 2022
Sales of warrants		$ 58,900,000
Warrants, issuance costs		200,000
Convertible notes hedge and warrant transactions cost net		20,000,000
Deferred tax liability adjustment to additional paid-in capital		9,400,000
Deferred income tax benefit		6,900,000
Liability for accrued income taxes		$ 2,500,000
0.25% Convertible Senior Notes Due 2022 [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Warrants holder’s option to purchase number of shares of company’s common stock \| shares		4.2
Warrants exercise price per share \| $ / shares		$ 115.8
0.25% Convertible Senior Notes Due 2022 [Member] \| Liability Component [Member]
Debt Instrument [Line Items]
Debt issuance costs	7,900,000
0.25% Convertible Senior Notes Due 2022 [Member] \| Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs	$ 2,900,000
0.25% Convertible Senior Notes Due 2022 [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price per share \| $ / shares		94.77
Percentage of closing price to trigger debt conversion	130.00%
0.25% Convertible Senior Notes Due 2022 [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price per share \| $ / shares		$ 115.83
Percentage of closing price to trigger debt conversion	98.00%
0.25% Convertible Senior Notes Due 2022 [Member] \| Scenario 1 [Member]
Debt Instrument [Line Items]
Debt instrument, convertible, threshold trading days \| d	20
Debt instrument, convertible, threshold consecutive trading days \| d	30
0.25% Convertible Senior Notes Due 2022 [Member] \| Scenario Two [Member]
Debt Instrument [Line Items]
Debt instrument, convertible, threshold trading days \| d	5
Debt instrument, convertible, threshold consecutive trading days \| d	5
0.25% Convertible Senior Notes Due 2022 [Member] \| Private Offering [Member]
Debt Instrument [Line Items]
Principal amount of long term debt	$ 350,000,000
0.25% Convertible Senior Notes Due 2022 [Member] \| Over-Allotment Options [Member]
Debt Instrument [Line Items]
Principal amount of long term debt	$ 50,000,000