Marketable Securities - Classified as Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 135,435	$ 164,845
Gross Unrealized Gain	108	65
Gross Unrealized Loss	(160)	(291)
Fair Value	135,383us-gaap_AvailableForSaleSecurities	164,619us-gaap_AvailableForSaleSecurities
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	56,618	62,208
Gross Unrealized Gain	43	16
Gross Unrealized Loss	(36)	(134)
Fair Value	56,625	62,090
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,126	49,343
Gross Unrealized Gain	7	5
Gross Unrealized Loss	(19)	(38)
Fair Value	39,114	49,310
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,605	19,280
Gross Unrealized Gain	21	25
Gross Unrealized Loss	(105)	(114)
Fair Value	17,521	19,191
Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,006	11,868
Gross Unrealized Gain	31	14
Gross Unrealized Loss	0	(4)
Fair Value	12,037	11,878
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,500	18,698
Gross Unrealized Gain	0	2
Gross Unrealized Loss	0	0
Fair Value	6,500	18,700
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,580	3,448
Gross Unrealized Gain	6	3
Gross Unrealized Loss	0	(1)
Fair Value	$ 3,586	$ 3,450

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

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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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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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

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-Publisher FASB

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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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