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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Stockholders' Equity and Employee Stock Plans - Additional Information (Detail)			1 Months Ended					3 Months Ended		12 Months Ended
	Jan. 01, 2018 shares	Apr. 26, 2017 shares	May 31, 2016 shares	Oct. 31, 2015 shares	Aug. 31, 2014 shares	Jan. 31, 2012	Sep. 30, 2011 Period shares	Mar. 31, 2018 USD ($) shares	Mar. 31, 2017 USD ($) shares	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized								5,000,000
Preferred stock, shares outstanding								0
Preferred stock, shares issued								0
Number of shares granted								785,400
Number of stock option outstanding, granted								0	0
Intrinsic value of options exercised \| $								$ 2,600,000
Compensation cost related to unvested stock-based awards granted, but not yet recognized \| $								$ 96,800,000
Nonvested awards, compensation cost not yet recognized, period for recognition								3 years
Capitalized stock-based compensation expense \| $								$ 0	$ 0
2003 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserve of common stock for future issuance								955,568
2003 Stock Plan [Member] \| Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of fair value of common stock on grant date								85.00%
2003 Stock Plan [Member] \| Stock options [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period								10 years
2003 Stock Plan [Member] \| Stock options [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period								4 years
2003 Stock Plan [Member] \| Stock options [Member] \| Greater 10% Ownership [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of fair value of common stock on grant date								110.00%
Minimum percentage of combined voting power								10.00%
2011 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserve of common stock for future issuance							1,000,000
Increase percentage of common stock outstanding								4.00%
Increase in reserve share		850,000	1,300,000
2011 Stock Option and Incentive Plan [Member] \| Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of fair value of common stock on grant date								100.00%
Expiration period								10 years
2011 Stock Option and Incentive Plan [Member] \| Restricted Stock Units for Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period								4 years
Description of vesting terms								The Company also grants RSUs. RSUs granted to new hires and merit grants to existing employees generally vest over a four-year period with 25% vesting at the end of one year and the remainder vesting quarterly thereafter.
2011 Stock Option and Incentive Plan [Member] \| Restricted Stock Units for Common Stock [Member] \| Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage at the end of period								25.00%
2011 Stock Option and Incentive Plan [Member] \| Performance-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period								3 years
Vesting performance period								1 year
Vesting service period								2 years
Description of vesting terms								The PRSUs provide for a target number of shares that generally vest over three years which includes a one-year performance period and two years of service-based vesting. The PRSUs vest contingent upon the Company’s achievement of annual revenue and annual operating margin targets for fiscal 2018 relative to the Company’s annual operating plan.
Vest contingent upon the company’s achievement of total operating expenses at the internal operating plan, percentage								110.00%
Award expiration date								Nov. 30, 2019
2011 Stock Option and Incentive Plan [Member] \| Performance-based RSUs [Member] \| Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted								74,621
2011 Stock Option and Incentive Plan [Member] \| Performance-based RSUs [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Earned percentage on target award amount, depending on level of achievement								200.00%
2011 Stock Option and Incentive Plan [Member] \| Performance-based RSUs [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Earned percentage on target award amount, depending on level of achievement								0.00%
2011 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserve of common stock for future issuance							500,000
Increase percentage of common stock outstanding						1.00%
Increase in reserve share	342,338
Program effective date							Nov. 08, 2011
Percentage in payroll of deduction base salary to acquire shares of common stock							15.00%
Offering period							24 months
Percentage of fair value of common stock on offering period							85.00%
Number of years, shares reserved for issuance increase						8 years
Number of stock option outstanding, granted								0
2011 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserve of common stock for future issuance							20,000,000
Number of purchase periods for offering \| Period							5
Inducement Stock Option Plan And Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period					10 years
Description of vesting terms								In accordance with the terms of the Inducement Option Plans, the Company issued options to purchase an aggregate of 290,000 shares of the Company’s common stock at an exercise price equal to the fair market value of a share of the Company’s common stock on the dates of grant of the options. The options, which have a ten-year term, vest at the rate of 25% of the shares on each of the first anniversary of the vesting commencement date with an additional 6.25% of the shares subject to the option vesting each quarter thereafter so long as the participant has not been terminated.
Number of stock option outstanding, granted					290,000
Inducement Stock Option Plan And Agreement [Member] \| Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage at the end of period					25.00%
Inducement Stock Option Plan And Agreement [Member] \| Quarterly Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage at the end of period					6.25%
Inducement Restricted Stock Unit Plan and Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Description of vesting terms								In accordance with the terms of the Inducement RSU Plans, the Company issued RSUs representing an aggregate of 290,000 shares of the Company’s common stock. The RSUs, which expire following settlement, vest at the rate of 25% of the shares on each of the first anniversary of the vesting commencement date with an additional 6.25% of the shares subject to the RSU vesting each quarter thereafter so long as the participant has not been terminated.
Shares available for grant					290,000
Inducement Restricted Stock Unit Plan and Agreement [Member] \| Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage at the end of period					25.00%
Inducement Restricted Stock Unit Plan and Agreement [Member] \| Quarterly Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage at the end of period					6.25%
2015 Equity Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserve of common stock for future issuance				100,000
2015 Equity Inducement Plan [Member] \| Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of fair value of common stock on grant date				100.00%
Expiration period				10 years
Increase in reserve share										350,000
2015 Equity Inducement Plan [Member] \| Restricted Stock Units for Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted								221,400		101,200