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Schedule of Reported Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | $ 1,470,729 | $ 1,304,711
Available-for-sale marketable securities, Unrealized Gain | 6,582 | 2,977
Available-for-sale marketable securities, Unrealized (Loss) | (3,406) | (2,821)
Available-for-sale marketable securities, Fair Market Value | 1,473,905 | 1,304,867
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 1,350,896 | 732,979
Marketable securities |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 1,349,970 | 871,321
Available-for-sale marketable securities, Unrealized Gain | 38 | 134
Available-for-sale marketable securities, Unrealized (Loss) | (2,029) | (431)
Available-for-sale marketable securities, Fair Market Value | 1,347,979 | 871,024
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 1,288,844 | 423,128
Long-term marketable securities |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 120,759 | 433,390
Available-for-sale marketable securities, Unrealized Gain | 6,544 | 2,843
Available-for-sale marketable securities, Unrealized (Loss) | (1,377) | (2,390)
Available-for-sale marketable securities, Fair Market Value | 125,926 | 433,843
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | $ 62,052 | $ 309,851

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References 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=75030427&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 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 + Details
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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://www.xbrl.org/2003/role/presentationRef -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 + Details
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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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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