Summary of Cash, Cash Equivalents and Marketable Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	$ 220,692	$ 122,651
Unrealized Gains	88	11
Unrealized Losses	(83)	(10)
Estimated Fair Value	220,697	122,652
Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	103,030	49,511
Unrealized Gains	4
Unrealized Losses	(3)
Estimated Fair Value	103,031	49,511
Marketable Securities Available-for-Sale
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	117,662	73,140
Unrealized Gains	84	11
Unrealized Losses	(80)	(10)
Estimated Fair Value	117,666	73,141
Cash \| Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	5,163	2,522
Estimated Fair Value	5,163	2,522
Money Market Funds \| Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	61,748	46,989
Estimated Fair Value	61,748	46,989
Corporate Debt Securities \| Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	36,119
Unrealized Gains	4
Unrealized Losses	(3)
Estimated Fair Value	36,120
Corporate Debt Securities \| Marketable Securities Available-for-Sale
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	67,753
Unrealized Gains	80
Unrealized Losses	(78)
Estimated Fair Value	67,755
U.S. Government Agency Securities \| Marketable Securities Available-for-Sale
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	49,909	73,140
Unrealized Gains	4	11
Unrealized Losses	(2)	(10)
Estimated Fair Value	$ 49,911	$ 73,141

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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