Antidilution adjustments of convertible note hedges.

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Class of warrant or right exercise price of warrants or rights issued.

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Debt instrument, convertible, maximum threshold percentage.

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Debt instrument issuance costs amortization period.

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Deferred financing cost, amortization period.

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Payments for Convertible Note Hedge, Net, Financing Activities

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Pledge percentage of capital stock.

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Expiration, mandatory redemption, or due date, in CCYY-MM-DD format, of the financial instrument issued in exchange for the original debt being converted in a noncash or part noncash transaction.

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-Name Accounting Standards Codification
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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount of a favorable spread to a debt holder between the amount of debt being converted and the value of the securities received upon conversion. This is an embedded conversion feature of convertible debt issued that is in-the-money at the commitment date.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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The price per share of the conversion feature embedded in the debt instrument.

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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No definition available.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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- Definition

Date the debt agreement requires the first payment to be made, in CCYY-MM-DD format.

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Face (par) amount of debt instrument at time of issuance.

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Description of the frequency of periodic payments (monthly, quarterly, annual).

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

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No definition available.

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The cash outflow to reacquire common stock during the period.

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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Debt - Additional Information (Detail) $ / shares in Units, shares in Millions			12 Months Ended
	Dec. 12, 2016 USD ($) d $ / shares shares	Apr. 27, 2015 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Debt Instrument
Debt instrument, net proceeds after issuance costs				$ 450,800,000
Repurchase of common stock			$ 200,304,000	$ 146,331,000	$ 299,949,000
Repurchase of stock, shares \| shares				6.8	15.6
Term of loan, years		5 years
Pledge percentage of capital stock		65.00%
1.25% Convertible Senior Unsecured Notes Due December 15, 2023
Debt Instrument
Aggregate principal amount	$ 460,000,000		$ 460,000,000	$ 460,000,000
Debt instrument, interest rate, stated percentage	1.25%
Debt instrument, net proceeds after issuance costs	$ 450,800,000
Payment for net cost of convertible note hedges net of warrant proceeds	33,000,000
Repurchase of common stock	$ 50,100,000
Repurchase of stock, shares \| shares	2.0
Senior notes maturity date	Dec. 15, 2023
Debt instrument, frequency of periodic payment	Payable semiannually in arrears on June 15 and December 15 of each year
Debt instrument, date of first required payment	Jun. 15, 2017
Debt instrument, conversion option expiration date	Sep. 15, 2023
Debt instrument conversion price \| $ / shares	$ 31.80		$ 31.80
Shares that would be issued upon conversion \| shares			14.5
Strike price per share of warrant \| $ / shares			$ 39.91
Debt instrument, convertible, carrying amount of equity component	$ 100,800,000		$ 100,800,000
Debt instrument, effective annual interest rate			5.00%
Financing cost	$ 7,200,000		$ 6,300,000
Debt issuance costs, amortization period			7 years
Unamortized discount			$ 94,000,000
Debt Instrument, convertible, remaining discount amortization period			6 years
Value of notes converted			$ 605,700,000
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 \| Conversion option one
Debt Instrument
Trading days measurement period \| d	20
Consecutive trading days measurement period \| d	30
Percentage of conversion price	130.00%
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 \| Conversion option two
Debt Instrument
Trading days measurement period \| d	5
Consecutive trading days measurement period \| d	5
Percentage of closing sale price of common stock and conversion rate product	98.00%
Maximum
Debt Instrument
Aggregate principal amount		$ 150,000,000
Commitment fee percentage of unused portion of credit facility		0.35%
Minimum
Debt Instrument
Commitment fee percentage of unused portion of credit facility		0.125%
Base Rate \| Maximum
Debt Instrument
Debt instrument, basis spread on variable rate		1.00%
Base Rate \| Minimum
Debt Instrument
Debt instrument, basis spread on variable rate		0.00%
London Interbank Offered Rate (LIBOR) \| Maximum
Debt Instrument
Debt instrument, basis spread on variable rate		2.00%
London Interbank Offered Rate (LIBOR) \| Minimum
Debt Instrument
Debt instrument, basis spread on variable rate		1.00%
Revolving Credit Facility
Debt Instrument
Financing cost			$ 2,300,000
Financing cost, amortization term			5 years
Revolving Credit Facility \| Maximum
Debt Instrument
Credit facility, borrowing capacity		$ 350,000,000