Investments - Portfolio of marketable securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available-for-sale securities:
Cost	$ 179,522	$ 195,958
Gross Unrealized Gains	14,157	12,675
Gross Unrealized Losses	(27,590)	(27,495)
Estimated Fair Value	166,089us-gaap_AvailableForSaleSecurities	181,138us-gaap_AvailableForSaleSecurities
Amounts classified as cash equivalents	(41,704)us-gaap_CashEquivalentsAtCarryingValue	(42,681)us-gaap_CashEquivalentsAtCarryingValue
Marketable securities cost	137,818us-gaap_MarketableSecurities	153,277us-gaap_MarketableSecurities
Marketable securities estimated fair value	124,385	138,457
Short-term deposits
Available-for-sale securities:
Cost	41,704	42,681
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	41,704	42,681
Mutual funds
Available-for-sale securities:
Cost	17,030	17,030
Gross Unrealized Gains	4,713	4,262
Gross Unrealized Losses	(272)	(322)
Estimated Fair Value	21,471	20,970
Corporate securities
Available-for-sale securities:
Cost	88,392	103,761
Gross Unrealized Gains	8,963	7,821
Gross Unrealized Losses	(25,277)	(23,732)
Estimated Fair Value	72,078	87,850
Corporate obligations
Available-for-sale securities:
Cost	32,396	32,486
Gross Unrealized Gains	481	592
Gross Unrealized Losses	(2,041)	(3,441)
Estimated Fair Value	$ 30,836	$ 29,637

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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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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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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