Income Taxes - Income Tax Expense Reconciles to Amount Computed by Applying Federal Statutory Rate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation to statutory rate:
Tax at federal statutory rate	$ 63,341	$ 31,965	$ 18,623
State taxes, net of federal benefit	4,911	2,344	1,384
Impact of foreign operations	(13,305)	(113)	(211)
Stock-based compensation	8,050	2,982	1,385
Tax credits	(10,616)	(5,637)	(415)
Other	506	(790)	182
Income tax expense	$ 52,887us-gaap_IncomeTaxExpenseBenefit	$ 30,751us-gaap_IncomeTaxExpenseBenefit	$ 20,948us-gaap_IncomeTaxExpenseBenefit
Reconciliation to statutory rate:
Tax at federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	2.70%	2.60%	2.60%
Impact of foreign operations	(7.40%)	(0.10%)	(0.40%)
Stock-based compensation	4.40%	3.30%	2.60%
Tax credits	(5.90%)	(6.20%)	(0.80%)
Other	0.40%	(0.90%)	0.40%
Effective Income Tax Rate Reconciliation, Percent, Total	29.20%	33.70%	39.40%

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 applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference, between reported income tax expense (benefit) and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, that is attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority interest income (expense), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, change in enacted tax rate, prior year income taxes, change in deferred tax asset valuation allowance, and other adjustments.

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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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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 tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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