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Schedule of Reported Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 487,503	$ 259,011
Available-for-sale marketable securities, Unrealized Gain	1,569	592
Available-for-sale marketable securities, Unrealized (Loss)	(1,347)	(2,967)
Available-for-sale marketable securities, Fair Market Value	487,725	256,636
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	120,039	191,978
Marketable securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	421,024	190,100
Available-for-sale marketable securities, Unrealized Gain	126	88
Available-for-sale marketable securities, Unrealized (Loss)	(62)	(92)
Available-for-sale marketable securities, Fair Market Value	421,088	190,096
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	91,100	140,262
Long-term marketable securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	66,479	68,911
Available-for-sale marketable securities, Unrealized Gain	1,443	504
Available-for-sale marketable securities, Unrealized (Loss)	(1,285)	(2,875)
Available-for-sale marketable securities, Fair Market Value	66,637	66,540
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	$ 28,939	$ 51,716

X

- Definition

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

+ References

No definition available.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

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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- Definition

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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- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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