Summary of Cash, Cash Equivalents and Marketable Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	$ 166,726	$ 196,113
Unrealized Gains	122	78
Unrealized Losses	(1)	(66)
Estimated Fair Value	166,847	196,125
Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	38,858	44,806
Unrealized Gains		7
Unrealized Losses		(1)
Estimated Fair Value	38,858	44,812
Marketable Securities Available-for-Sale
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	127,868	151,307
Unrealized Gains	122	71
Unrealized Losses	(1)	(65)
Estimated Fair Value	127,989	151,313
Cash \| Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	6,030	4,561
Estimated Fair Value	6,030	4,561
Money Market Funds \| Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	24,982	21,193
Estimated Fair Value	24,982	21,193
U.S. Government Agency Securities \| Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	4,999
Estimated Fair Value	4,999
U.S. Government Agency Securities \| Marketable Securities Available-for-Sale
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	24,604	17,628
Unrealized Gains	8
Unrealized Losses		(6)
Estimated Fair Value	24,612	17,622
Corporate Debt Securities \| Cash and Cash Equivalents
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	2,847	19,052
Unrealized Gains		7
Unrealized Losses		(1)
Estimated Fair Value	2,847	19,058
Corporate Debt Securities \| Marketable Securities Available-for-Sale
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	96,691	133,679
Unrealized Gains	112	71
Unrealized Losses		(59)
Estimated Fair Value	96,803	$ 133,691
U.S. Treasuries \| Marketable Securities Available-for-Sale
Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	6,573
Unrealized Gains	2
Unrealized Losses	(1)
Estimated Fair Value	$ 6,574

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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-Publisher FASB
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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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