Schedule of Reported Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
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

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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