Income Taxes - Provisions for Income Taxes Computed by Applying Statutory Federal Income Tax Rates (Detail)	12 Months Ended
Dec. 27, 2014	Dec. 28, 2013	Dec. 29, 2012
Income Tax Disclosure [Abstract]
Expected tax at federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	1.80%	0.30%	0.00%
Research credits	(11.40%)	4.90%	0.00%
Stock-based compensation	14.70%	(12.20%)	(3.90%)
Change in valuation allowance	(25.30%)	(34.20%)	(33.50%)
Other	2.00%	0.80%	(0.20%)
Effective tax rate	16.80%	(5.40%)	(2.60%)

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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