Investments Portfolio of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale securities:
Cost	$ 195,958	$ 229,948
Gross Unrealized Gains	12,675	15,930
Gross Unrealized Losses	(27,495)	(5,484)
Estimated Fair Value	181,138us-gaap_AvailableForSaleSecurities	240,394us-gaap_AvailableForSaleSecurities
Cash equivalents cost	(42,681)us-gaap_CashEquivalentsAtCarryingValue	(61,909)us-gaap_CashEquivalentsAtCarryingValue
Cash equivalents estimated fair value	(42,681)us-gaap_CashEquivalentsAtCarryingValue	(61,909)us-gaap_CashEquivalentsAtCarryingValue
Marketable securities cost	153,277us-gaap_MarketableSecurities	168,039us-gaap_MarketableSecurities
Marketable securities estimated fair value	138,457	178,485
Short-term deposits
Available-for-sale securities:
Cost	42,681	60,909
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	42,681	60,909
Mutual funds
Available-for-sale securities:
Cost	17,030	15,722
Gross Unrealized Gains	4,262	5,061
Gross Unrealized Losses	(322)	0
Estimated Fair Value	20,970	20,783
United States government securities
Available-for-sale securities:
Cost		50,356
Gross Unrealized Gains		23
Gross Unrealized Losses		0
Estimated Fair Value		50,379
Corporate securities
Available-for-sale securities:
Cost	103,761	69,806
Gross Unrealized Gains	7,821	9,961
Gross Unrealized Losses	(23,732)	(5,208)
Estimated Fair Value	87,850	74,559
Corporate obligations
Available-for-sale securities:
Cost	32,486	31,356
Gross Unrealized Gains	592	885
Gross Unrealized Losses	(3,441)	(276)
Estimated Fair Value	29,637	31,965
Commercial paper
Available-for-sale securities:
Cost		1,799
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Value		$ 1,799

Estimated fair value of marketable securities.

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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 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.

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

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