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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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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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

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

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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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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 cash outflow to reacquire common stock during the period.

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Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands, shares in Millions			3 Months Ended		12 Months Ended
	Dec. 12, 2016 USD ($) Customer shares	Apr. 27, 2015 USD ($)	Mar. 31, 2019 USD ($) $ / shares shares	Apr. 01, 2018 USD ($) shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares
Debt Instrument
Repurchase of common stock			$ 156,468	$ 134,276
Repurchase of stock, shares \| shares			4.5	2.9
Pledge percentage of capital stock		65.00%
1.25% Convertible Senior Unsecured Notes Due December 15, 2023
Debt Instrument
Aggregate principal amount	$ 460,000		$ 460,000		$ 460,000
Debt instrument, interest rate, stated percentage	1.25%
Debt instrument, net proceeds after issuance costs	$ 450,800
Payment for net cost of convertible note hedges net of warrant proceeds	33,000
Repurchase of common stock	$ 50,100
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					$ 31.70	$ 31.70
Shares that would be issued upon conversion \| shares					14.5
Strike price per share of warrant \| $ / shares			$ 39.78
Debt instrument, convertible, carrying amount of equity component			$ 100,800			$ 100,800
Debt instrument, effective annual interest rate			5.00%
Financing cost			$ 5,100			$ 7,200
Debt issuance costs, amortization period			7 years
Unamortized discount			$ 76,400
Debt Instrument, convertible, remaining discount amortization period			4 years 8 months 12 days
Value of notes converted			$ 578,100
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 \| Conversion option one
Debt Instrument
Trading days measurement period \| Customer	20
Consecutive trading days measurement period \| Customer	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 \| Customer	5
Consecutive trading days measurement period \| Customer	5
Percentage of closing sale price of common stock and conversion rate product	98.00%
Maximum
Debt Instrument
Aggregate principal amount		$ 150,000
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
Financing cost, amortization term			5 years
Revolving Credit Facility \| Maximum
Debt Instrument
Credit facility, borrowing capacity		$ 350,000