Marketable Securities - Marketable Securities Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 51,007	$ 164,845
Gross Unrealized Gain	140	65
Gross Unrealized Loss	(138)	(291)
Fair Value	51,009	164,619
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,608	62,208
Gross Unrealized Gain	122	16
Gross Unrealized Loss	(73)	(134)
Fair Value	25,657	62,090
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,424	49,343
Gross Unrealized Gain	0	5
Gross Unrealized Loss	(31)	(38)
Fair Value	12,393	49,310
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,800	19,280
Gross Unrealized Gain	2	25
Gross Unrealized Loss	(23)	(114)
Fair Value	4,779	19,191
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		18,698
Gross Unrealized Gain		2
Gross Unrealized Loss		0
Fair Value		18,700
Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,705	11,868
Gross Unrealized Gain	16	14
Gross Unrealized Loss	(9)	(4)
Fair Value	5,712	11,878
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,470	3,448
Gross Unrealized Gain		3
Gross Unrealized Loss	(2)	(1)
Fair Value	$ 2,468	$ 3,450

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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